jan feb11 cover final 11-4

B A R C N E W S L E T T E R

In the Forthcoming issue

1. Recent Developments on Radioprotection by Selenium CompoundsK. Indira Priyadarsini, et al.

2. Modeling of deformation behaviour of hcp metals usingCrystalplasticity ApproachApu Sarkar and J.K. Chakravartty

3. Multi-Detector Environmental Radiation Monitor withMultichannel Data Communication for Indian EnvironmentalRadiation Monitoring Network (IERMON)M.D. Patel et al.

4. Single Phase Flow Simulation of Industrial Scale Agitated TanksK.K. Singh, et al.

5. Hollow Fibre Liquid Membranes: A Novel Approach for NuclearWaste RemediationS.A. Ansari, et al.

6. Experiments on reinforced concrete structures; sub-assemblages and components for seismic safety–postinstalled anchorsAkanshu Sharma et al.

7. A Material Transfer System using Automated Guided VehiclesR.V. Sakrikar et al.

8. TB-PCR kit for diagnosis of tuberculosisSavita Kulkarni et al.


ISSUE NO. 318 I JAN - FEB 2011 I i

Editorial Note ii

62nd Republic Day Address by 1Dr. Ratan Kumar Sinha, Director, BARC

Our Gratitude to Dr. Homi J. Bhabha 13Dr. S.V.K. Rao

Technology Development Articles

Development of Technologically Important Crystals and Devices 16S.G. Singh et al.

Heavy Liquid Metal Technology Development 28A. Borgohain et al.

Indigenous Development of Silicon PIN Photodiodes Using 34a 4" Integrated Circuit Processing FacilityAnita Topkar et al.

Development of Room Temperature NH3 Gas Sensors based on Ultrathin SnO2 Films 39Sipra Choudhury et al.

Development of online radon and thoron monitoring systems 45for occupational and general environmentsJ.J.Gaware et al.

Feature articles

Formal Model Based Methodology for Developing Software 52for Nuclear ApplicationsA. Wakankar et al.

Development of Digital Radiotherapy Simulator: 63A Device for Tumour Localization, Radiotherapy Planning and VerificationD.C. Kar et al.

News and Events

National Conference on Advances in Nuclear Technology (ADNUTECH 2010): a report 70

DAE-BRNS Workshop on “High Resolution Gamma Ray Spectrometry 72(HRGS-2010)”: a report

Workshop on Protection against Sabotage and Vital Area Identification: a report 74

Valedictory function of the Health Physics Training course-15th Batch: a report 75

National Science Day Celebrations at BARC 77

BARC Scientists Honoured

Contents

ISSUE NO. 318 I JAN - FEB 2011 I 1


62nd Republic Day Addressby

Dr. Ratan Kumar Sinha, Director, BARC

“Dear colleagues,

My greetings to all of you on the occasion ofthe 62nd Republic Day of our country. As all ofyou know, in the year 1950, the Constitution ofthe sovereign democratic republic of India wasadopted and world’s largest democracy wasborn.

Every year, as a part of this celebration, wesalute our national flag. We also remember andsalute the members of our armed forces, whoprovide security to our country.

This function provides us an opportunity to takestock of our achievements during the year. Theprogrammes of our Organisation of more than15,000 colleagues are extremely diverse andvoluminous. Therefore, on this occasion today,I intend to cover only a few representativeactivities, providing a glimpse of ourachievements during the recent past.

Research Reactors

As all of you are aware, last year, two of theresearch reactors Canadian Indian Reactor(CIRUS) and Dhruva have successfullycompleted 50 years and 25 years of veryproductive operation. CIRUS continued tooperate at an availability factor of around 87%until December 31, 2010, when the reactor waspermanently shut down.

As a part of upgrading the core of the Apsara

reactor, decommissioning activities of the reactorand reactor systems have already beencompleted. Demolition of the existing reactorbuilding will commence soon to enableconstruction of the new building. Detailedengineering of various reactor systems ofupgraded Apsara is currently in progress.

Research reactor Dhruva has also been takenup for refurbishment and replacement of variousequipment and components to ensure itscontinued high availability.

Dr. Ratan Kumar Sinha, Director, BARC addressing theBARC freternity

2 I ISSUE NO. 318 I JAN - FEB 2011


The Advanced Heavy Water Reactor(AHWR) Critical Facility was operated forvarious experiments. A mixed pin clustercarrying thorium oxide as well as natural uraniumpins was loaded in four different locations ofthe AHWR Critical Facility. Criticality wasachieved with all these loadings and the observedcritical height was in close agreement with theestimated critical height. Multiple foils wereirradiated to obtain the reaction rates in variousenergy regions and SAND-II code was usedfor the spectrum unfolding.

Testing of nuclear detectors in graphite reflectorregion continued. Moderator level coefficientmeasurements were carried out and observedvalues matched with predicted ones. Reactivitymeasurement due to loading of a clustercontaining Thoria and Uranium pins was carriedout satisfactorily. Facility was also utilised forlarge volume sample irradiations for NeutronActivation Analysis (NAA).

The conceptual design of a High FluxResearch Reactor (HFRR) to be built at ournew campus at Vizag, has been completed.HFRR is designed primarily to meet the largerequirements of high specific activity radio-isotopes and to provide enhanced facilities forbasic research in frontier areas of science andfor applied research related to development andtesting of nuclear fuel and reactor materials.

Advanced Heavy Water Reactor (AHWR)

The AHWR Thermal hydraulic Test Facility(ATTF) is being setup at R&D Center, Tarapur,in collaboration with Nuclear Power Corporationof India Ltd. (NPCIL), to establish thermal andstability margins as well as to test the fuellingmachine at prototypical conditions. The variouswork modules of the project like civil,mechanical, electrical, instrumentation and

control are at an advanced stage of execution.

Thermal hydraulic analysis of AHWR with LowEnriched Uranium (LEU) was carried out toestimate the thermal margin. It was found thatadequate thermal margin exists with LEU in theAHWR core. A feasibility study was also carriedout for the power uprating of AHWR usingpumped circulation with LEU.

In order to reduce the plutonium requirementsof the AHWR initial core, various options ofpartial loading of AHWR initial core werestudied. Detailed studies related to AHWRequilibrium core with Th-LEU fuel for a targetburnup of 60 GWd/te were carried out. An initialcore with LEU fuel has been designed withdesirable operational features during refuelingand transition to the equilibrium core.

The design of the secondary shut down systemof AHWR was modified to have eight injectiontubes at two elevations. The jet dynamics wasmodeled using an indigenously developedmethodology and the worths were estimated.

Compact High Temperature Reactor(CHTR) and 600 MWth High TemperatureReactor (HTR) for Hydrogen Production

Solid modeling of CHTR systems andcomponents was completed. CHTR fuel rodsimulator costing about 1% of the imported optionwas developed. Fabrication of molten salt loopand corrosion test facility for high temperaturereactor application has been completed.

The challenging task of treating the doubleheterogeneity effect created by lumping the fuelinto particles and those into pebbles has beendone using the Reactivity equivalent PhysicalTransform (RPT) method. The results werecompared with reference results from Monte



Carlo simulation of a pebble, in which doubleheterogeneity has been treated explicitly.

CHTR physics design simulations wereperformed with new design modifications suchas use of thinner control rods for finer control,Reduction in the available locations (18 to 12)for control rod etc. Efforts were made to minimisethe single CR worth at criticality by varying thecontent of burnable poison.

Study of Thorium utilisation in PressurisedWater Reactors

A study of possibility of thorium utilisation in aPressurised Water Reactor (PWR) was madeby considering the (Th-LEU (19.75% U-235))MOX fuel. PWR cores fuelled with thoriumusing different fissile compositions were studied.

LWR studies

An updated WIMS library in 172 groups hasbeen generated in-house with burn-up chainextended up to 252Cf. This library contains 185nuclides and resonance integral tabulation for48 resonant nuclides, including several minoractinides with temperature extended up to2500°K. This library has performed successfullyfor the VVER simulations.

Fuel development and supply

BARC has the responsibility of supplyingplutonium bearing fuels for the Fast ReactorProgramme, including Fast Breeder Test Reactor(FBTR) and Prototype Fast Breeder Reactor(PFBR) (under construction) at Kalpakkam.

For the production of U-Pu mixed carbide fuelpins for FBTR, new technologies like Laserwelding for the fuel pin end-plug closure andLaser engraving unit for fuel pin numbering have

been qualified and are being inducted into theproduction line.

The regular production of Mixed Oxide (MOX)fuel pins for PFBR has started at Advanced FuelFabrication Facility (AFFF) and a new fuel pinwelding line has been recently commissioned.The experimental PFBR MOX fuel beingirradiated at FBTR has now reached a burn-upof 107,000 MWd/T, exceeding the design targetburn-up of 100,000 MWd/T.

BARC is also involved in R&D on metallic fuelfor the advanced fast breeder reactors with highbreeding ratio. Thermophysical properties likephase transition temperatures, solidustemperature and eutectic temperature betweenU-15%Pu fuel and T-91 cladding has beendetermined. A glove box train consisting ofinjection casting, demoulding and eddy currentinspection of fuel slugs has been set up at AtomicFuels Division (AFD)

For the AHWR Fuel Fabrication mock-upfacility project, radiation resistance remoteviewing system has been developed indigenouslyfor hot cell and shielded enclosure applicationsfor AHWR fuel fabrication.

Based on the post irradiation examination of thethoria-4%plutonia mixed oxide fuel elements,two of the intact fuel elements were certified tobe fit for re-irradiation in CIRUS reactor. Thesetwo fuel elements, along with fresh fuel elementscontaining thoria-8%plutonia of AHWR fueldesign, manufactured at AFFF, werereconstituted into an irradiation rig and loadedinto CIRUS for irradiation. This exercise hashelped us to arrive at the procedure for qualityassurance for reloading and re-irradiation ofexperimental fuels in the test loops of researchreactor. Both the irradiated pins, despite being



cooled for more than twelve years in the spentfuel storage pool, could withstand the irradiation,till the closure of the CIRUS.

Neutron radiography set-up for irradiated fuelpin at CIRUS was installed and commissioned.After trial runs with unirradiated fuel pin, neutronradiography of irradiated Pressurised HeavyWater Reactor (PHWR) fuel pin andexperimental thoria-plutonia MOX fuel pinswere carried out. Defects like, fuel cracks,hydriding of clad, and swelling and dislocationof fuel were detected. Details of fuel pin likepellet gap, spring inside the pin at the end werealso clearly visible in the neutron radiograph.Decrease in fuel column length was observedin the experimental thoria-plutonia fuel pinshaving low density pellets. Formation of centralvoid was found in experimental thoria-plutoniaMOX high burnup fuel pin.

Detailed post-irradiation examination has beencarried out on Zr-2.5Nb-0.5Cu loose fit gartersprings, taken out from 10 high flux channels,five each from Kakrapar Atomic Power Station-1 (KAPS-1) and Narora Atomic Power Station-1 (NAPS-1) PHWR reactors. These gartersprings were retrieved during the EMCCRoperation after around 10.5 Effective FullPower Year (EFPY) of operation.

An indigenous micro-wave heating system (1-6kW power), adapted and retrofitted to existinghot-cell (without any alteration), was tested. Itwill be used for the dissolution of irradiated thoriabased fuels and materials and also for actinideseparation studies of advanced fuels.

Reprocessing and Waste Management

Reprocessing plants at Trombay and Kalpakkamcontinued to operate safely and satisfactorily.Radioactive wastes generated from nuclearinstallations both at Trombay & Kalpakkam were

managed safely. In addition, during the year,radioactive wastes generated during partialdecommissioning of Apsara was managed quiteefficiently.

The development of oblong-shaped metallicmelter to achieve higher through-put in wastevitrification process was completed and the unitwas commissioned.

As a part of automation programme forplutonium reconversion laboratory, extensive trialruns were taken on rotary vacuum drum filterand continuous screw calciner. Automation ofreconversion laboratory, besides increasing thethrough-put, helps in bringing down the load onoperator and man-rem expenditure.

Towards deep geological repository programme,developmental activities were continued. Settingup of an underground research laboratory hasbeen initiated. This laboratory will facilitateconducting various experiments under inactiveconditions, such as studying the effect of vitrifiedwaste canister on the host rock, its remotehandling aspects, validation of codes formigration of various radio-nuclides, etc.

An incinerator for radioactive solid waste atRadioactive Solid Waste Management Site(RSMS), BARC, Trombay has been refurbishedand commissioned. A volume reduction factorof hundred was achieved and the airborneactivity during the incineration was belowdetection limit, indicating effectiveness of airtreatment system.

Installation and testing of Resin Fixation Facilityfor conditioning of spent resins in polymer matrixis nearing completion at RSMS, Trombay. Thefacility has incorporated the process forimmobilisation of spent resins in specific cementalso.



At Centralised Waste Management Facility(CWMF), Kalpakkam, a new facility forretrieval, volume reduction and disposal of storedpressure tubes has been designed and a workorder has been released after obtainingnecessary safety clearances. A facility for meltdensification has been in continuous use fortreatment of plastic/polythene waste. Basedupon the experience gained from the facility, anew scaled up facility with certain modificationis being set up.

Feasibility studies have been initiated forvitrification of High Level Waste (HLW) fromAHWR and Fast Reactor Fuel Cycle Facility(FRFCF) in sodium borosilicate glass matrix.Irradiation of typical sodium borosilicate glasscomposition to study long term radiation stabilityof glass matrix with respect to alpha radiationand recoil damage has been completed. Thermalproperty of acid and molten glass resistantrefractory material has been enhanced byaddition of bubble alumina.

Further development work is in progress for ColdCrucible Induction Melting technology forvitrification of HLW. Green heating experimentshave been carried out successfully. Model-based design of cold crucible for hull meltdensification has been completed.

Separation of useful isotopes such as 106Ru, 90Yetc. was continued for supplying these materialsfor medicinal use. Techniques for quality controlof the recovered 90Y were also developed.

An underground research laboratory is being setup in one of the captive sites of the Department.This laboratory will help in conducting variousexperiments such as study of the effect ofheat generating canister on the disposalenvironment, development of methodologies foremplacement/retrieval of the canister remotely,

validation of various codes for predicting themigration of activity, mechanical stresses inthe host rock due to the digging of the tunneletc.

Health, Safety and Environment

Environmental Studies

Environmental surveys for the baseline studiesof the new uranium mining projects atTummalapalle (A.P.) and new BARC campusat Vizag are currently in progress. Pre-operational survey at new Nuclear Power Plantsites of Hissar in Haryana and Mithivirdi inGujarat were also initiated.

Studies on assessment of radiological impact ofthe proposed uranium tailings pond at Seripalliin Nalgonda district of Andhra Pradesh haveconcluded that the radiological impact of theproposed uranium tailings pond is trivial up to aperiod of 2000 years and will be of no concernafter this period.

A Cone Beam Optical Computed Tomography(CBOCT) system has been designed, developedand tested for obtaining 3-D dose distributionfrom advanced radiotherapy equipment usingpolymer gel dosimeter. The facility for preparingpolymer gel dosimeter has also been established.The system will be useful for dose verificationin radiotherapy.

There was a need for dosimeters in the doserange of 100 to 1000 Gy for low dose applicationsof food irradiation, especially for mangoirradiation. Accordingly, two new dosimeterswere developed in the dose range mentionedusing i) Glycine & (ii) Lithium formate. Thesesystems being indigenously developed are cost-effective.



Analysis of the data on the effect of radiationon congenital malformations, such as mentalretardation (MR) and cleft lip/palate (CLP),using case control methodology, generated underthe three year epidemiological study project, hasbeen completed. The results indicate nostatistically significant excess relative risks forthe occurrence of these malformationsattributable to natural background radiation.

Safety studies

BARCOM Test Model for Ultimate LoadCapacity Assessment

The 1:4 size BARC Containment (BARCOM)Test Model simulating the 540 MWe PHWRinner containment was subjected to over-pressure test till the first appearance of crackwas realised. This occurred at a pressure of0.2207 MPs, which is 1.56 times its designpressure. The failure initiation was attributed toinelastic strains developed in the discontinuityregions of Main Air Lock and Emergency AirLock. The data collected during thepressurisation has been compared with analyticalpredictions reported by various InternationalRound Robin Participants, including that of in-house code ULCA from BARC.

Cyclic Fracture Tests on Narrow GapWelded (NGW) SS304LN Stainless SteelPipes

Cyclic fracture tests were conducted to addressthe concern about the effect of cyclic loadinganticipated during a seismic event. Apart frompipes with cracks in base metal; conventionallywelded pipes using Submerged Metal ArcWelding (SMAW) and those welded using HotWire Pulsed Gas Tungsten Arc Welding(GTAW), with narrow gap were also tested. Theinvestigation has revealed that the Cyclic Tearingand monotonic fracture resistance of narrow gapGTAW is superior to SMAW, supplementing the

other advantages of GTAW, such as lowerresidual stress and reduced susceptibility tosensitisation.

A supercritical test facility was set up earlierto investigate heat transfer, pressure drop andstability behaviour of supercritical fluids. Thefacility was earlier operated with supercriticalcarbon-dioxide up to 90 bar pressure. The facilitywas modified for operation with SupercriticalWater (SCW) up to 250 bars and 400 oC andexperiments are going on.

Channel Heat up Studies for PHWR

Pressure Tube is expected to have acircumferential temperature gradient during flowstratification for a small break Loss of CoolantAccident (LOCA) situation in a PHWR. A trialexperiment for asymmetric heating(circumferential) of pressure tube for 220 MWePHWR at atmospheric pressure has beencarried out with a 19 Fuel Pin Simulator.

Seismic Qualification of glove boxes

The seismic qualification tests were performedon different configurations of glove boxes viz.single glove box, glove box train and doublemodule glove box. The studies concluded thatthe glove boxes could safely withstand a groundacceleration of 0.2 g. Necessary modificationshave been identified, which would enable themto withstand higher acceleration.

AHWR safety

As a part of demonstration of safety marginsavailable in AHWR, analyses were carried outto identify plant symptoms generated duringBeyond Design Basis Event for “decrease ininventory” category. It was shown that, evenfor the scenario involving a 200% break at inletheader along with un-availability of Emergencycore Cooling System (ECCS) and loss of



moderator as a heat sink, symptoms can beidentified and sufficient time is available for welldefined operator action to prevent fueltemperature excursion.

Physics

CIRUS Reactor has been used for neutrontomography of hydrogen blister in Zircaloy andfor neutron based phase contrast imaging ofsubstances embedded inside dense material.

A high power/high energy Nd:Glass laser systemof 20 joules and pulse width 300 – 800 picosecond with focusable intensity better than5 x 1014 watts/cm2 has been indigenouslydeveloped. This laser system has been used togenerate shock pressure exceeding 25 Mega barin several materials.

The performance of the indigenously developedFolded Tandem Ion Accelerator (FOTIA) hasbeen steadily improving. Recently, the protonbeam current from this accelerator has reacheda high value of 2 micro amp, one of the bestvalues one can get from a low energyaccelerator of this type.

Materials and metallurgy

A process for the separation of rare earthscomprising of yttrium as major constituent, alongwith erbium, holmium, ytterbium as minorcomponents from merchant grade phosphoricacid, employing DNPPA+TOPO as synergisticextractant mixture, was developed by selectivescrubbing with 40% sulphuric acid. The scrubsolution was further subjected to sodium doublesulphate precipitation, followed by re-dissolutionand oxalate precipitation and conversion to oxide.The rare earth product was purified to > 99%,with respect to sodium by digesting with hotwater. Counter-current tests showed overall90% recovery.

Production of U-metal ingots was continued andutilised for fuel fabrication for research reactors,proposed Sub-cirtical Facility at Purnima andspecific requirements at Metallif Fuels Division(MFD).

Development of tubular solid oxide fuel cell(TSOFC)

Process has been established to fabricate singleSOFC cell of tubular configuration (both inanode and cathode supported ) through co-isostatic pressing followed by co-firing. Anodesupported cell was found to give a maximum of62 mW.cm-2 power density when tested at900 oC. Work is in progress to improve theperformance by addressing the issues relatedto fuel distribution, sealing and current collectionof SOFC cell.

Development of catalyst material fordecomposition of sulphuric acid in I-Sprocesses for hydrogen production

A process has been developed for bulkpreparation of iron oxide based catalyst pebblesfor use in the decomposition of sulphuric acid inI-S processes for hydrogen production. Thecatalyst showed high (~78%) yield forconversion of H

2SO

4 to SO

2 with long run

stability. Bulk preparation is under progress forcarrying out pilot test in Chemical TechnologyDivision

The stress corrosion crack growth rates inAHWR simulated high purity water at 288degree C in a recirculating test facility have beensuccessfully established on the materialsproposed to be used in AHWR. SS 304L withaddition of 0.08 and 0.16 wt% nitrogen wereused in sensitized condition and also in as –received materials with 20% warm working(non-sensitised) conditions. These results on our



materials to be used in AHWR provide importantinputs about crack growth behaviour of thematerials. Stainless steels have been protonirradiated at FOTIA and at PELLETRON at4.8 MeV and at a temperature of 300 degreeC. The Radiation Induced Segregation (RIS) hasbeen successfully characterised using a newapproach of electrochemical and atomic forcemicroscopic characterisation.

Lasers and Accelerators

10 MeV Linear Accelerator (Linac)

The depth dose distribution of the electron beamof the 10 MeV RF linear electron acceleratorwere measured using B3 Radiochromic films.The electron beam has been employed fordemonstrating industrial applications towardscross-linking of poly-ethylene rings (more than1 lakh pieces), diamond coloration, Teflondegradation and production of photoneutrons.

BARC- ECIL RF LINAC

The 9 MeV cargo scanning RF Linac wasoperated with beam parameters of 9 MeV, 60mA, 7 microsecond duration at 250 Hz pulserepetition rate. Experiments on electron beamtransport and beam focusing at X-ray target werecarried out. X-ray spot size of 2.5 mm diameteron the target and a dose of 24 Gy/minute at 1meter from the target was measured. The X-ray collimator has been developed and installed.

AVLIS programme

The knowledge of the velocity of atomic beamand thermal ion content is important in variousprocesses involved in our AVLIS programme.The experimental measurements of atomic flux,flow velocity and thermal ion content werecarried into a 100kW zirconium evaporator usingmicro-balance and Langmuir probes.

The measurements carried out up to 3270 K ata height of 400 mm were compared with theestimated values for the thermal velocity,terminal Mach number velocity and velocity dueto internal conversion of energy from meta-stable energy levels upto 5000cm-1 into kineticenergy.

Demonstration of narrow CPT Resonance

As a part of the ongoing programme ongenerating an ultra precision frequency referencefor atomic clock, a coherent population trappingsignal with a width of 14 KHz was achievedthrough use of a special vertical cavity laser withRF modulation and side band generation.

Test Blanket Module (TBM) developmentfor ITER programme

As a part of Test Blanket Module developmentfor Indian ITER programme, joint MHDexperiments at high magnetic fields with BARC-IPR Test-sections at Institute of Physics,University of Latvia (IPUL) have commencedand experimental test-sections made of austeniticsteels have been tested.

Development of 15 kV, 6 kW Electron BeamMelting Machine

An indigenous 15 kV, 6 kW Electron beammelting machine was designed and developed.This computer controlled machine will be usedfor production of high purity Uranium andThorium alloys in the form of buttons, rings andfingers by EB melting and consolidation.

DM&AG

An Autonomous Guided Vehicle (AGV) basedMaterial Transfer System has been developed,which can be used in manufacturingenvironments for autonomous transfer or



distribution of materials from a supply point toseveral machining shops. The same solutioncan also be used for unmanned transfer ofradioactive materials in nuclear installations likeBoard of Radiation & Isotope Technology(BRIT), Nuclear Fuel Complex (NFC), etc.The system autonomously monitors stock levelsat the delivery points and initiates appropriatetransfers to maintain uniform satisfaction at alldelivery points.

ChTG/RMP

Design, development and manufacturing of aprototype batch of Micro Electro MechanicalSystems (MEMS) based pressure and opto-mechanical pressure sensors using micro-nanoengineering technology has been successfullycompleted.

With the successful criticality crossing of aprototype Advanced Multi-section metallic HighSpeed Rotor, capacity of producing theseparative output of the existing machines willbe doubled.

About 1800 acres of land in Challekere Talukof Chitradurga District has been acquired forsetting up of Special Material Facility during theXII Plan.

Prototype Tritium monitors based onBremsstrahlung technique have beensuccessfully developed.

Computational Analysis Division

A five (5) Teraflop High PerformanceComputing Facility has been set up at the Facilityfor Electromagnetic Systems (FEMS), BARC,Visakhapatnam. A variety of in-house codeshave been parallelized for efficient use of thissystem. By end-2011, it is proposed to upgrade

this to a 20 Teraflop system.

An electromagnetic coil-gun, acceleratingmetallic projectiles weighing 30-50 grams tovelocities upto 100 meters/sec, has been set upand in regular operation. A 2-D MHD computercode, developed in-house for modelling this gun,has yielded good agreement with experiments,and is being used for optimization. The gun,which yields reproducible results, will be usedfor studying high velocity impact and penetrationphenomena.

Development of Instrumented and CaliperPipe Inspection Gauges (PIGs)

In continuation with the development ofinstrumented pigs and caliper pigs for in-lineinspection of pipelines, tools for 24" nominal borepipelines have been integrated and delivered toIndian Oil Corporation (IOC). They are testedin wet evaluation facility of IOC R&D Centre,Faridabad. The instruments use state-of-the-artdigital signal processing (DSP) electronics foracquisition and on-line processing of magneticflux leakage data. 12" instrumented PIGdeveloped earlier is upgraded and successfullyrun for 200 km of Allahabad-Kanpur section ofIOC pipeline. The defect report has been usedfor repairing severe defects.

Basic Research in Chemistry

An indigenous synthesis of the ligand, MIBI hasbeen developed and used successfully for thepreparation of the heart imaging agent, Tc-MIBIcomplex. Following the approval by theRadiopharmaceutical Committee, the product iscurrently being marketed by BRIT and suppliedto the hospitals of Maharashtra. This is an importsubstitute and has reduced the cost of themedicine drastically.



A new pyromethene (PM) laser dye, withsignificantly improved photo-chemical stabilitythan the commercially available dye has beendesigned. The new dye shows similar lasingefficacy as that of the commercial one, and iscurrently being considered for use in the U-enrichment programme.

Using Microwave Plasma Chemical VapourDeposition (CVD) technique, high quality andhighly oriented CVD diamond thin films weregrown on silicon wafer (1-5 cm2 area) to makealpha detectors, configured in the form of metal-insulator-semiconductor hetero-structure. Thedetectors were successfully tested for alphasensitivity in air, using electroplated 238Pu source.

A granular biofilm based process fordenitrification of high strength nitrate-bearingeffluents generated in the nuclear industry hasbeen developed. Denitrification of upto12,000 mg/l nitrate was achieved in lab scalebio-reactors. Effluent nitrate/nitrite levels at theend of 24 h cycle time were less than 10 mg/l,which can be safely discharged to theenvironment.

A biological process is under development forthe removal of sulphate from sulphate-bearingbarren effluents, such as those produced atUranium Corporation of India Ltd. (UCIL),Jaduguda. In this method, a series of three bio-reactors employing sulphate reducing bacteriawas used to sequentially bring down sulphateconcentration from 18,000 ppm to below 100ppm. Experiments are being conducted toreduce operational cost by making use of cheapcarbon sources for the growth of the SRB.

A fuel cell based hydrogen burner has beendeveloped for burning the deuterium formedduring chemical decontamination and thedeuterium formed in stoichiometric excess in themoderator cover gas during normal operation.

The method consists of a fuel cell and a heatedpalladium catalyst column as pre-treatmentfacility for removing oxygen from deuterium. Thecatalyst column ensures the removal of oxygenfrom deuterium and the pure deuterium comingfrom the catalyst column is allowed to passthrough the fuel cell, where it combines withoxygen to form D

2O.

Nuclear Agriculture

A new mungbean variety TM-2000-2 (Pairymung) with early maturity and disease resistance,suitable for rabi and utera (rice fallow) cultivationconditions has been released and notified forChhattisgarh State. The total number ofTrombay crop varieties released and notified byMinistry of Agriculture, Government of Indiafor commercial cultivation has now reached 39.In groundnut, two simple sequence repeat (SSR)markers were found to be tightly linked with rustresistance gene for use in marker assistedbreeding.

Rainwater harvesting facility was developed atagricultural farm of Nuclear Agriculture & Bio-Technology Division (NABTD), BARC,Gauribidanur for breeder and nucleus seedproduction.

45 Nisargaruna solid waste treatment plantswere established in various places in the countryunder the guidance from BARC.

Technology Transfer and (AdvancedKnowledge and Rural TechnologyImplementation) (AKRUTI) programme

Besides filing three international patents, andone national patent based on in-house R&Dactivities, seven new technologies in the area ofsafe drinking water, one in medical electronicsand one in solid waste management weretransferred to industry successfully.



As a part of development of BARC Centre forIncubation of Technology (BARCIT), civil,electrical, air-conditioning work at the fiveTechnology Incubation Cells are in advancedstages of completion and are likely to start theoperation by March 2011, under Phase I of theoperation of BARCIT.

Among the ten MoUs signed with differentorganisations during the year, commercial useof KRUSHAK Irradiator, Lasalgaon byMaharashtra State Agriculture and MarketingBoard (Pune) and Barge Mounted Sea WaterReverse Osmosis Plant for Production ofDrinking Water, by IREL are noteworthy.

BARC has signed seven AKRUTI Tech Packagreements for deployment of technologies inrural sector. These include four privatecompanies, 2 NGOS and one womanentrepreneur. Tissue Culture Laboratory atAKRUTI-CARD (Centre for Appropriate RuralDevelopment) in Anjangaon-Surji, Amravati hasbecome operational.

Isotope Hydrology based identification of borewell location has been successfully implementedin AKRUTI-CARD (Community Action forRural Development), Amaravati in a waterscarce area. The farmers were asked to drillborehole about 60 m deep at the identified siteat Anjangaon village, Amravati district,Maharashtra. The borehole is now yielding~30,000 Litres of water per hour and is aperennial source of good quality drinking waterfor 5- 6 villages. Encouraged by the success ofthe model project, six more projects areunderway.

Medical Services

As you all know, our BARC hospital, along withits 12 zonal dispensaries caters to more than87,000 registered beneficiaries, While every

effort is being made to improve our on-lineservices, two new machines viz., Radial FluroX-ray machine and Computerised RadiographySystem have been installed and are being usedfor needy patients. The newly renovated ward4A is now made available, along with 18 normalbeds, 6 air conditioned beds and 14 emergencybeds to the patients. It is also proposed tointroduce new dispensary at Kharghar, NaviMumbai for the convenience of the beneficiariesof Navi Mumbai. Land for this dispensary hasalready been occupied, and further work isunder progress. It will take 3 years for fullfunctioning of this dispensary.

A multiplex polymerase chain reaction (PCR)protocol, involving two genes for detection oftuberculosis, was standardised and validated. Ithas been given to BRIT for the formulation of aTB detection kit and its commercialisation.

177-Lu labeled dotatate synthesised in-house isbeing used for radiotherapy of neuroendocrinetumors at RMC. With the installation of a newDual Head Gamma Camera, it has becomepossible to handle more number of cancerpatients in RMC now.

XI Plan activities

We are shortly coming to the close of our XIth

plan project activities. In order to formulate ourprogrammes for the XIIth plan project, it isessential to critically review our progress andjudiciously extrapolate to decide about closingthe projects or, if necessary, continuing underthe next plan. This process is currently on throughvarious group Boards. Based on the outcomeof this activity, we will be in a position to put upnew programmes under the next plan. I earnestlyappeal to all of you to timely contribute to thisprocess.



Physical Protection

Physical protection of our Centre and its variousinstallations is of paramount importance. I amsure, all my colleagues will understand that theconcern of security has further increased in thepresent time. I strongly urge our Fire Servicepersonnel to maintain a constant vigil on thevarious establishments of our centre and striveto improve their coordination with security andthe concerned Divisions.

I also compliment all officers and staff of ourCentre for extending their cooperation with thesecurity personnel in discharging their dutieseffectively for implementing the higher level ofsecurity procedures. Finally, I urge all mycolleagues in our Centre to remain vigilant andalert in the present environment.

The contribution made by the personnel of ourLandscape & Cosmetics Maintenance Sectionis aptly demonstrated by the beautiful ambienceof this venue.

Conclusion

My dear colleagues, on one hand, we havecommitted ourselves to be at the frontiers ofscience and technology at international level. On

the other hand, we also have a commitment toprovide benefits of our knowledge andtechnologies to the Indian society at large, at alllevels. You may know very well that it has beenour mandate to develop national capability in allareas associated with nuclear sciences andtechnologies and our fulfillment of this mandate,inspite of an embargo regime, has been the keyto make us strong enough to acquire apronounced international stature. This spirit ofself-reliance and development of indigenoussolutions must continue. Currently, we are inthe process of formulating our ideas for the XIIFive Year Plan period. Let us carry out a rigorousanalysis of any residual gaps and vulnerabilitiesand formulate projects and activities to bridgethe gaps indigenously.

I am sure, all of you will continue to put in yourefforts so as to sustain our tradition of excellencein the years to come.

Friends, therefore, on this very special day, letus firmly resolve and rededicate ourselves tocontinue our pursuit of excellence in the frontierareas of nuclear science and technology for thebetterment of life of our people.

Jai Hind ”.



Our Gratitude to Dr. Homi J. Bhabha

Dr. S.V.K. Rao

(Retd. Head, Ceramics Section, Metallurgy Divn., BARC)

In 1956, I joined the AEET, Atomic EnergyEstablishment Trombay, (later renamed BARC)in the Metallurgy Division, operating from theOld Yatch Club (OYC) Building near theGateway of India. This building housed Dr.Bhabha’s office, Administrative, Accounts andPurchase Divisional offices and some Labsincluding the Metallurgy Lab.

The entire BARC campus, as we see now, wasnon-existent and it was the vision of Dr. Bhabhaand his team which has made it possible.

Through my interaction for some 8 years withthe Administrative, Accounts and PurchaseDivisional staff and with some of the other

Scientists and Engineers in the OYC building, Icould gather my impressions about Dr. Bhabhaand how he created such a huge ScientificEstablishment at Trombay, in such a short time.

Initially the Honourable Prime Minister PanditJawaharlal Nehru invited Dr. Bhabha and askedhim to plan the entire developmental process ofAtomic Energy for power generation and otherpeaceful applications for India. Dr. Bhabha wasgiven Carte Blanche to put his plan into action.

Dr. Bhabha himself selected a team of wellqualified, experienced and very competentScientists and Engineers representing all themajor Scientific and Engineering fields and gavethem full freedom to plan, recruit staff, expandand diversify, and set up their R&D Labs andinstallations. Several newly appointed Scientistsand Engineers were deputed to Canada, USA,UK and France to work there and gainexperience in operating power reactors. I wasfortunate to have been deputed to the AtomicEnergy of Canada Ltd. (AECL), where I hadthe opportunity to carry out researchinvestigations on the development of CeramicNuclear Fuels and their irradiation behavior. Dr.Lewis, the Chairman of AECL, was known tobe a great friend of Dr. Bhabha from theirCambridge University days and extendedtraining facilities to a large number of Scientistsand Engineers from BARC. The CIRUSResearch Reactor at BARC is the outcome ofthis Indo-Canadian co-operation.

Most of the engineering equipment andinstallations, for large scale Civil Engineering

Dr. Homi J. Bhabha



constructions and infrastructure andsophisticated scientific equipment were acquiredfor AEET, through the offices of Dr. Bhabha asSecretary, DAE and Chairman/AEC. Thisexpedited the entire process.

Dr. Bhabha identified reputed and wellestablished large private organizations withproven track records, competence and integrityand gave assignments to them for the executionof the jobs. Thus, by a combination of all thesefactors, he could build such a huge establishmentin such a short time.

Dr. Bhabha wanted the R&D labs of all thescientific disciplines to be under one roof, as itwould facilitate carrying out multidisciplinaryR&D projects. So we were all asked to designour respective Labs on a modular design basis,so that, each module would have all the servicefacilities. Thus the Modular Laboratories cameinto being. Dr. Bhabha was particular that thebuilding should not block the view of the Sea,therefore, he wanted it to be raised on pillars.Our Chief Engineer (Civil) and his staff told me,that they went through tense moments ofsuspense when Dr. Bhabha came and scrutinizedthe 3- dimensional scale model of the building.He studied the model for a long time silentlyand seriously and finally gave his approval. Hewas very fond of Architecture and wanted allthe buildings on the campus to be of differentgeometrical shapes, so that, they did not lookstereotyped and boring. The whole campus waslandscaped with lavish lawns, flower beds andgardens and thus provided pleasantsurroundings.

One of the major steps that Dr. Bhabha hadtaken was, to delink the Public ServiceCommission from our staff recruitmentprogramme. He justified this by saying, thatscientific work in Atomic Energy areas was of

a very specialized nature and our multidisciplinaryqualified Scientists could take care of staffrecruitments. Subsequently, the Training Schoolwas started in 1957, which has been providingqualified entry level Scientists and Engineers forvarious programmes and projects of BARC aswell as DAE.

Initially the designations of the Scientific staff,to give a few examples, were Junior ScientificOfficer, Scientific Officer, Senior ScientificOfficer, Principal Scientific Officer and ChiefScientific Officer etc. Dr. Bhabha wanted tocreate an atmosphere of equality among thescientific community, which wouldn’t be rankconscious. To this end, he changed thedesignations in such a way, that all wereScientific Officers- SOs with only ascendingalphabets within brackets, which showed theirseniority. Thus they were changed to SO(SC),SO(SD), SO(SE), SO(SF), SO(SG) etc.

Dr. Bhabha was fully aware of the hardships oflack of accommodation, commuting over longdistances, and unaffordable medical expensesof a big-city life for new entrants to ourorganization. He took care of all these problems.He planned a huge township of staff quarters inAnushaktinagar. As this ambitious plan wouldtake several years to complete, he arranged topurchase outright, any group of newlyconstructed residential buildings put up for sale,wherever available in the city and suburbs. Suchgroups of buildings were purchased andconverted to staff quarters in many locations inthe city and suburbs. From all these widelyscattered locations, depending on public transportfor commuting to the Establishment in Trombaywas real hardship. To solve this, Dr. Bhabha hadput forth, that in a large establishment withthousands of employees, in case of a nuclearevent, the entire staff would have to be vacatedvery rapidly. This would require a large fleet of



buses on the campus, maintained in runningcondition. BARC is thus one of the few R&Dcentres in Mumbai, which offers transportfacilities to its employees.

According to Dr. Bhabha, most of theLaboratories handle radioactive materials in anAtomic Energy Establishment and if the staffmembers get exposed to radiation, despite allprecautions, the treatment would require veryspecialized medical facilities. Eventually a verylarge centralized full-fledged Hospital was builtand set up, with numerous dispensaries in manylocations. The entire medical treatment for thestaff and their families is highly subsidized.

I can never forget the unfortunate day, January24th, 1966. On that day in the evening, we werestanding outside, opposite the ModularLaboratory, waiting for our buses. I suddenlysaw a couple of cars come rapidly and stop onthe Mod Labs side of the road. Across the road,I could see Dr. Bhabha and others getting downfrom their vehicles. Dr. Bhabha was silentlylooking at the Mod Labs building which was inan advanced stage of construction, as thoughtaking a last look. After observing for a while,they all went away. None of us standing thererealized that it was to be our last glimpse of Dr.Bhabha. That night Dr. Bhabha left by an AirIndia flight to Paris. Next day we were allshattered to see screaming headlines in thenewspapers that Air India Flight AI 101 hadcrashed in Europe by colliding against the snowclad Mount Blanc peak of the Alps and that therewere no survivors. In fact, Dr. Bhabha was totake the same flight exactly one day before theprevious night, for which he was booked. Butdue to a mishap in one of the Technical PhysicsLabs at South Site, Dr. Bhabha had to visit thesite and postpone his journey by a day, only toleave by the fateful flight. It was the hand ofdestiny. It was a great loss of a person who had

done so much for all of us, and for the wholenation.

Thus, today the staff of BARC are housed indecent staff quarters, commute in BARC buses,and have excellent medical facilities and asregards working environment, all the buildings,Labs as well as offices are centrally airconditioned with a beautiful environment of wellmaintained green lawns, flower beds andgardens. For the scientists, the legacy of Dr.Bhabha continues, which enables them to workin an atmosphere of equal opportunity,encouragement and recognition of merit. Unlikemany other Government Departments, ourBARC Administrative, Accounts, Purchase,Stores and Security staff are exceptionallysincere, dedicated and very helpful, consistentwith the BARC culture and carrying on thelegacy of Dr. Bhabha.

After Dr. Bhabha, successive Chairmen of AECand Directors of BARC, have taken BARC andall the constituent Units under DAE, to greaterheights of achievements.

Now after retirement, whenever I interact withour BARC Doctors and staff, the dedicatedcare, sincerity, courtesy and commitment theyshow, reminds me of the legacy of Dr. Bhabha.And occasionally whenever I phone ourAdministration or Accounts, for someclarification, I find that even very senior officers,unlike in many other Govt. Departments, respondpromptly with courtesy and sincerity, reflectingthe culture inculcated by Dr. Bhabha.

Even today, 21 years after retiring from BARC,all this makes me to continue to be grateful toDr. Homi J. Bhabha.


B A R C N E W S L E T T E RTECHNOLOGY DEVELOPMENT ARTICLE

Development of Technologically ImportantCrystals and Devices

S.G. Singh, M. Tyagi, D.G. Desai, A.K. Singh, Babita Tiwari, Shashwati Sen,

A.K. Chauhan and S.C. Gadkari

Technical Physics Division

A b s t r a c t

Device-grade single crystals of technologically important materials for use as scintillators in nuclear radiation

detection, lasers and optical devices are grown in Crystal Technology Section of the Technical Physics Division.

The expertise has been developed to establish crystal growth processes and design and fabricate crystalgrowth equipment. In addition, single crystals of new materials to be used in neutron and gamma detection are

also being studied and developed currently. The processing, characterization and testing of devices are carried

out using in-house facilities as well as in collaboration with other Divisions.

Introduction

Though research on nano-materials is in fullswing, single crystals are still on the top in vitalareas like radiation detection (γ-ray, X-ray,neutron, IR), solid state lasers, optical windowsetc, and even in nano technologies like thin filmsand quantum dots, the substrates used areinvariably made from single crystals. Due to theirtechnological importance and denial by developedcountries there is a dedicated facility for singlecrystal growth in BARC (Crystal TechnologySection, T.P.D.). Broadly there are threecategories of crystals that are of current interest;(i) Scintillator crystals, (ii) Laser host crystalsand (ii) Optical crystals. These are grown frommelts using Czochralski and Bridgemantechniques for the single crystal growth.

The materials which convert the energy of highenergy electromagnetic radiation (short wavelength X-ray, gamma-ray, UV) or particles

(electron, proton, alpha etc) into visible light arecalled scintillator materials and used in radiationdetection. Since the discovery of NaI:Tl dopedscintillator crystal in 1948 [1], this field developedvery fast and presently many brilliant scintillatormaterials are in fray. Few important scintillatorsamong these are CsI:Tl, Bi

4Ge

3O

12 (BGO),

PbWO4 (PWO), PbMoO

4 (PMO), CdWO

4

(CWO), ZnWO4, Lu

2SiO

5 (LSO), Lu

2Si

2O

7,

LaBr3:Ce, Li

6Gd(BO

3)

3 (LGBO), Li

2B

4O

7

(LBO), NaBi(WO4)

2 (NBW) etc [2-4]. Among

these crystals CsI, LGBO, LBO, PMO andNBW are presently being grown in our lab whileNaI, PWO and BGO have been grown in thepast.

Some oxide and halide crystals doped with rareearth elements (Nd, Yb, Ho etc) are importantsolid state materials for generating laser light invisible to infrared region. Important among theseare Nd:Y

3Al

5O

12 (Nd-YAG), Al

2O

3:Cr (ruby),

double tungstates NaY(WO4)

2 (NYW),



NaGd(WO4)

2 (NGW), NaLa(WO

4)

2, NBW,

KY(WO4)

2, KGd(WO

4)

2 etc. [5]. Currently, we

are involved in the growth of Nd doped NYWand Yb doped NGW crystals. These crystalswill be used in the diode-pumped high power q-switched lasers due to their broad absorption andemission bands arising from their disorderedstructures.

Optical window is a piece (mostly circular butsometimes rectangular, optically flat and paralleldisc) of a transparent optical material that allowslight (for a wavelength range of interest) into anoptical instrument isolated from vacuum or othermedium. Highly transparent optical windows indeep UV and IR region are technologicallyimportant. The materials to be used in theseapplications should have large band gap, isotropicand of good mechanical properties. Most popularmaterials used in optical windows are CaF

2, LiF,

BaF2, ZnS etc [6]. At present we are involved

in the growth of farmer three crystals.

Other crystals that have been grown in our labin the past are lead germanate, Al

2O

3, YAG, KCl,

NaCl and KBr etc.

Crystal Growth Techniques andInstruments

The crystal growth process involves a changeof phase, where the molecules of the materialgradually, uniformly and continuously lose theirrandom character (in liquid form) and achievecrystalline solid character. Single crystal growthproceeds on a seed crystal (may be of samematerial) that provides a nucleation center forthe growth. In the absence of a seed crystal, itis necessary for a system to super-cool or toattain a certain degree of super-saturation. Suchsuper-saturated solutions are in the metastablestates. Due to thermodynamic fluctuations, tinysolids called nuclei emerge when the critical size

of the solid favors the reduction of free energy.This process is known as “nucleation”. Oncethe system (vapor, melt, or solution) is in thermalequilibrium with its nucleus, the latter is capableof growing by attaching more and more materialto it, and this process is termed as “growth”.

There are various methods for the growth ofsingle crystals e.g. melt growth, high temperaturesolution growth, low temperature solution growth,vapor deposition growth, hydrothermal growthetc. [7]. Nearly 80% of all the single crystalsare grown by melt growth techniques. Due torelatively faster growth rates the melt growth issuitable for large scale production. Differenttechniques employed for the melt growth, aremainly (i) Czochralski technique, (ii) Bridgmantechnique, (iii) Float Zone technique and (iv)Verneuil technique. Among these Czochralski andBridgman techniques were used to grow mostof the halide and oxide single crystals formaterials study as well as for the industrialproduction. A brief description of these twopopular single crystal growth methods is givenhere.

Czochralski Technique

This technique was first developed by JanCzochralski (after which it was named), a polishchemist, in 1918 [8]. The Czochralski technique(Cz) is a popular method of crystal growthbecause it can produce large, dislocation freecrystals at a relatively faster rate. In Cz techniquecrystal is grown by slow pulling of a seed/wire/capillary from the free surface of a meltcontained in a crucible. A growth station, tocontain crucible and minimizes heat losses (byconduction and radiation), is made usingappropriate ceramic tubes, felts, and wools.Material to be grown is melted in the crucible byheating it in a suitable furnace (resistive heating,RF heating, Arc heating). A seed is lowered in



to the melt, and then pulled (at a rate 0.2-5 mm/h) along with rotation (5-25 rpm) at a slow rateafter achieving dynamic equilibrium at the solid-melt interface. After the completion of crystalgrowth with desired length, the process isterminated by suitably adjusting pull rate andtemperature at the solid-melt interface. Thegrown crystal is, then, cooled down to roomtemperatures at a slow cooling rate suitable forthe material.

During the growth the melt temperature is nearlyconstant in normal conditions (no stoichiometricdeviation due decomposition and dissimilarevaporation of melt components). The shape ofthe crystal can be determined by controlling thediameter of the growing crystal through themanipulation of the melt temperature and pullrate depending on properties of the materialunder consideration.

Theoretically, every material that meltscongruently and does not undergo any phasetransition during cooling, can be grown by thistechnique but there are some practical restrainwhich put some limits on the material propertieswhich can be grown by this technique [7]. Theselimits are:

i) Suitable crucible material (should beunreative, withstand high temperatures,easy in cleaning, easy in fabrication, e.g.Pt, Ir etc).

ii) Material should have a low vaporpressure. (Though there are modifiedmethod for the growth of such materialsbut not very convenient)

iii) Thermal conductivity of the materialshould be high (to conduct away the heatreleased from crystallization at thesolid-melt interface).

iv) Materials in crystalline form should nothave pronounced cleavage planes.

Bridgman Technique

This method is based on the work of Bridgmanin 1925 [9]. This is a popular technique to growsingle crystals of various halides. In this methodtemperature gradient moves slowly relative to acrucible (vertically or horizontally) until the meltin the crucible solidifies. The main economicadvantage of the method is simple basicapparatus, and little operator attention.Disadvantages arise from the contact betweencontainer and melt/solid which can give spuriousnucleation, sticking of the crystal ingot inside thecrucible and consequently generating thermal andmechanical stresses. Therefore to chooseappropriate crucible material and its properprocessing and design are importantconsiderations. The system consists of twoheating zones controlled independently andseparated from each other using a baffle toincrease the temperature gradient and minimizetemperature fluctuations (Fig.1). A cruciblecontaining the material is kept in the upper zone(hot zone) for complete melting then it is slowlylowered (1-5 mm/h) to the lower zone (coldzone) through an optimized temperature gradientuntil complete solidification.

A modified form of Bridgman method andprobably simplest method for directionalcrystallization is gradient freeze technique. Inthis method freezing isotherm is moved by slowlyreducing the power input to the furnace. Themain advantage lies in absence of any movementof either furnace or crucible which eliminatesany possibility of vibration or other mechanicalproblems. Though it is difficult to keep a constantgrowth rate throughout the crystal growthprocess due to a relatively small temperaturegradient (otherwise temperatures at the top ofthe furnace will be out of limit), though in somecases it is achievable by a segmented coolingprogram in accordance with the temperaturegradient to keep the rate of movement of freezing



isotherm constant.

Fluorides crystals are grown in vacuum Bridgmanfurnace which consists of vacuum chambercontaining a graphite heater. Electrodes andtranslation mechanism are isolated from vacuumchamber by different types of sealing. Thegrowth usually commence under high vacuumconditions.

Growth of Single Crystals

Scintillator Crystals

There are two categories of scintillator crystalsthat are grown at present namely (i) halides (CsI,NaI) and (ii) oxide crystals (PWO, PMO, ZWO,BWO, NBW). Halide crystals are generallygrown by Bridgman technique while oxidecrystals are grown by Czochralski technique.

Alkali Halide Scintillator Crystals

High quality single crystals of alkali-metal halidematerial are important as optical elements andas scintillation crystals in various types ofradiation detectors. Among these sodium iodide(NaI) and cesium iodide (CsI) activated withthallium occupy important place in gamma-rayspectroscopy and high energy particle detection.Scintillation properties and radiation hardness ofthese crystals are highly sensitive to crystalgrowth condition and post growth treatment.

These crystals are generally grown in cruciblesof noble-metals (platinum, platinum-alloy, iridiumetc.), silica glass or ceramic employing theBridgman technique. While the noble-metalcrucibles are very expensive, the silica glass andceramic crucibles have several inherentproblems such as crucible contamination and thegrown crystals adhering to the crucible.Extraction of grown crystals is very difficult andinvariably requires an inversion of the ampoule

Fig. 1: Schematic of Bridgman furnace for growth of alkalihalide crystals.

at high temperatures [10]. Here we describe thegrowth of cesium iodide crystals up to size of 40mm diameter and 40 mm length employing twodifferent methods

(i) Using graphite crucibles by verticalBridgman technique:

Single crystals of cesium iodide were grown inthe resin impregnated graphite crucibles [10].To demonstrate the use of the present method,a graphite crucible that had polished innersurfaces was loaded with the high purityanhydrous CsI (having 0.2% Tl) material andplaced in a silica glass ampoule. The ampoulewas evacuated and sealed under a pressure of10-2 mbar. A home-built Bridgman crystal growthsystem (Fig.1) was used that has a three zonefurnace operating in the normal ambientconditions by two independently controlled heaterelements.

The crucible sealed in the silica glass ampoulewas located in the upper zone and thetemperature was raised to about 650°C to meltthe material. After attaining equilibrium theampoule was lowered at a rate of about 1.5 mm/h through a temperature gradient of about 20°C/cm. The lowering was stopped when the cruciblein the silica glass ampoule reached the lowestzone and held here at about 550°C for 2 h before



finally cooling down to the room temperature ata rate of about 50°C/h. The silica glass ampoulewas cut open and the grown crystal could beeasily removed from the graphite crucible. Both,the ampoule and the crucible were reusable forthe next several experiments.

(ii) Using carbon coated silica by gradientfreeze technique:

A crystal growth furnace has been designed tohave a positive temperature gradient from topto bottom. Plot ‘a’ of Fig. 2 shows the gradientof the furnace with a blank crucible.Temperature profile in the melt is shown in plot‘b’ in the figure. Silica crucibles of one inchdiameter and having conical bottom were usedfor the growth. Carbon coating on the innersurfaces of the crucible was carried out bycracking of organic solvents at high temperatures

in an inert ambient. As-coated crucible was thentransferred in a vacuum furnace and annealedat 1100ºC. High pure (99.995%) and dry CsIand Tl (0.2 mole%) were taken in the carboncoated crucible and sealed under 10-3 mbarrunning vacuum at 200ºC. Crucible was thenplaced inside the furnace on a growth stationand temperature of the furnace was raised sothat the bottom of the crucible was at 640ºC(about 20ºC higher than the melting temperatureof the CsI). The melt was kept at thistemperature for about 4 h and then the furnacewas cooled at a rate of 4ºC/h until completesolidification of the melt into single crystal.Photograph of a polished CsI:Tl single crystal isshown in Fig. 3.

Though both the methods yielded good qualitycrystals, the later one is simpler and is moresuitable for production of the crystals at

industrial levels.Characterization ofgrown crystals wasdone by recordingtransmission andphotoluminescencespectra. Typicaltransmission andl u m i n e s c e n c espectra are shownin Fig. 4. Scintillationproperties weretested on a homebuiltgamma spectrometer.Linearity of thepulse height responseof a detectorfabricated usingthe grown crystalwas checked up to1332 keV gammaphoton. A calibrationcurve for thedetector is shown in

Fig. 2: Temperature gradient of gradientfreeze furnace with blank crucible (a) andwith crucible containing melt (b).

Fig. 3: Photograph of a polished singlecrystal of CsI:Tl grown by gradient freezetechnique in carbon coated crucible.

Fig. 4: Transmission (a) andluminescence spectra of CsI:Tl shown inFig. 3.

Fig. 5: Calibration line (a) of gamma detectorfabricated using crystal shown in fig.3 alongwith typical gamma spectra of 137Cs (b).



Fig. 5 and a typical 137Cs gamma spectrum isshown in the same figure exhibiting an energyresolution of ~7.8% at 662 keV which iscomparable to or better than reported values.

Oxide Crystal Scintillators

High density, ultra radiation-hard luminescentoxide crystals are forerunners in the fray forapplications in high energy particle detection inultra high energy particle accelerator like LHC.Search for an ideal scintillator crystal having highdensity, ultra radiation-hardness, fast decay time,inert to ambient and high light output is going onfor the past half century. Bi

4Ge

3O

12, PbWO

4,

PbMoO4, CdWO

4, ZnWO

4, Lu

2SiO

5:Ce,

Lu2Si

2O

7:Ce, Li

2(1-x)Y

2xSO:Ce, and NaBi(WO

4)

2

are a few crystals which fulfill most of the, ifnot all, properties of an ideal scintillator. Amongthese Lu

2SiO

5:Ce, Lu

2Si

2O

7:Ce, Li

2(1-x)Y

2xSO:Ce

are the most prominent candidates owing to theirhigh light yield and fast decay constant but theirgrowth is relatively difficult due to their highmelting temperatures (> 2000ºC). Anotherdrawback is their high cast due to the use oflutetium which is very rare. On the other handBi

4Ge

3O

12, PbWO

4, PbMoO

4, and NaBi(WO

4)

2

are materials that are relatively cheap and haveall properties of ideal scintillator except their lowlight yield which is not a crucial parameter in thehigh energy physics. These crystals are relativelyeasy to grow and are very much cast effectivetherefore can be produced at large scale to beused in large size detector systems.

These crystals are grown by the Czochralskigrowth technique. For the crystal growth,synthesized polycrystalline material orconstituent oxides was taken in a platinumcrucible (typically 50 mm diameter and 50 mmheight) and was placed inside a growth station.Heating was carried out at a rate of about 100ºC/h until complete melting of the material. Themolten material was allowed to soak for 1-2 h atthe temperature 30-50 ºC above the melting point.

To start the growth process, a seed crystal or aplatinum wire in absence of a seed crystal, isused. Seed crystal/Pt wire is slowly lowered totouch the melt surface and allowed there forsome time to attain thermal equilibrium with themelt. After that, pulling is started according topredetermined parameters using crystal growthsoftware though initially few changes have tobe made manually. The grown crystals arecooled down to room temperatures at a uniformrate (typically 30- 50ºC/h) depending on thematerial.

Various studies have shown some aspects of thecomplex relation between the crystal growthparameters and the resultant optical properties[11, 12]. The most severe problem during growthis stoichiometric variation due to decompositionof the material at elevated temperature andselective evaporation of the constituent oxides.Coloration, frequent cracking, inclusion, coreformation in the grown crystals are theconsequences of the stoichiometric variationsduring the growth. Other reason of the colorationin the crystals could be extrinsic impurities.Growth parameters, related problems and theirremedies of individual crystals are as follows.

(i) PbWO4 (PWO)

Single crystal of lead tungstate grown undernormal conditions turned yellowish showing anabsorption band at 420 nm. The yellow colorationof PbWO

4 crystals may arise due to the

stoichiometric deviation and/or presence of traceimpurities in the starting material. In leadtungstate PbO evaporates selectively and singlecrystal deficient in PbO has various defectsrelated to Pb centers. To compensate for thePbO losses from the melt a known amount ofPbO is added in the initial charge. But byconducting several growth runs it was establishedthat stoichiometric deviation is not the only factorresponsible for the coloration. It is, thus, apparent



that the coloration is caused by other defects/trace impurities too. Studies have shown thatgrowth ambient also had a pronounced effecton the coloration. Using already crystallizedcharge and oxygen rich ambient colorless crystalcould be grown. A gradual change in color ofsingle crystals from yellow color to colorless insuccessive experiments is shown in Fig. 6.Cracking problem of this crystal is highlydepended on the after-growth cooling rates. Adetailed study showed that cracking could beprevented (for crystals having diameter >20 mm)only if the cooling rate was less than 20ºC/h.Further, it was found to be independent of thegrowth direction. We believe that crackingproblem in PbWO

4 is due to the cleavage planes,

which for this crystal is (101), known to getcleaved by application of a very little force.

(ii) PbMoO4 (PMO):

The single crystal growth was carried out bythe Czochralski technique, using an automaticdiameter-controlled crystal puller (Cyberstarmodel: Oxypuller). For the growth of 20mmdiameter and 50 mm long crystals, a pull rate of2 mm/h and a crystal rotation rate of 20 rpmwere employed [12]. Seed crystal used for thegrowth was oriented along the c-axis. Crackingand coloration are the major problems faced withthe Czochralski growth of PMO crystals. Apartfrom the cooling rate and orientation the mainreason behind cracking of this crystal was foundto be the stoichiometry variation during thegrowth. In lead molybdate, unlike PWO, theselective evaporation of MoO

3 took place which

makes crystal Mo deficient.

Therefore to grow crack-free crystals one hasto take utmost care to compensate for the MoO

3

stoichiometry. Fig. 7 shows the photographs ofcrystals grown under identical conditions butusing starting charges of different compositionsand under different ambient viz., (a)stoichiometric/ in air (b) stoichiometric/ in argon,(c) 1% excess of PbO/ in air, (d) 1% excess ofMoO

3/ in air and (e) 1% excess of MoO

3/ in

argon. The photographs show clearly that thecrystal having excess of PbO like (a), and (c)shows high density of microcracks. On the otherhand, crystals grown using charges ofstoichiometric composition in argon ambient (b)or those from charges having an excess of 1%MoO

3 (d) and (e) did not crack either during

growth/annealing or on subsequent handling and

Fig. 6: Color transformation from yellow to transparentin PbWO

4 crystals.

Fig. 7: PMO crystals grown using differentstoichiometric starting charges under different ambient:(a) stoichiometric/air, (b) stoichiometric /Ar, (c) 1wt% Pbexcess/air,(d) 1wt% Mo excess/air, and (e) 1wt% Moexcess/Ar.

Fig. 8: Transmission spectra of PMO crystals grownusing different stoichiometric starting charges:(a) stoichiometric/air, (b) stoichiometric /Ar,(c) 1wt% Pb excess/air, (d) 1wt% Mo excess /air,and (e) 1wt% Mo excess/Ar.



also showed superior transmission characteristicsas shown in Fig. 8.

The results show that the crystals grown fromcharges containing slightly excess of MoO

3 are

more resistant to cracking, whereas an excessof Pb promotes the generation of microcracks.This is an important result from the point ofcrystal cracking which shows that to obtain acrack-free crystal the starting charge must beslightly rich in MoO

3.

(iii) NaBi(WO4-)

2 (NBW)

Single crystals of NBW were grown in air bythe Czochralski technique employing automaticdiameter controlled Cyberstar crystal pullers,having a 50 kW induction heater in Oxypullermodel (axial gradient 60°C/cm) and 12 kWmolybdenum silicide resistance furnace in TSSGmodel (axial gradient 6°C/cm). A uniform pullrate of 2 mm/h and a rotation of 15 rpm wereemployed for growing crystals of 20 mmdiameter from the melt contained in 50 mmdiameter platinum crucibles. A uniform postgrowth cooling rate of 40°C/h was employed inthe regular crystal growth experiments. Twotypes of initial charges were used for the crystalgrowth; (i) material synthesized by sintering ofconstituent oxides at 750°C for a total durationof about 100 h, in multiple segments involvinggrinding and mixing after every 24 h, (ii)transparent crystal chunks of previously growncrystals [13]. Typical photographs of threecrystals referred as A, B and C, grown from thetwo differently prepared starting charges undertwo different temperature profiles are shown inFig. 9.

It can be seen that diameter of A-type crystalsgrown from sintered charge under low gradients(6°C/cm-1) is not well controlled along withyellow coloration. Though the use of a hightemperature gradient was helpful in the precise

diameter control (crystal B) but coloration stillpersist in the crystal. Also the segregation of animpurity phase material can be seen at the bottomsuggesting the presence of other impure phasesalong with NBW. This problem was solved byusing a charge refined by multiple crystallizationand large temperature gradient (crystal C). TheC-type crystals show better radiation hardnessas compared to the other two types crystals [4].

(iv) BaWO4

The growth process is somewhat similar to thatdiscussed above for the growth of PbWO

4

crystals. But the problem in this case is the highmelting point i.e. 1475ºC of the material whichis close to softening temperature of the Pt-crucible. The pulling rate was initially fixed at 4mm/h and a fixed rotation rate of 15 rpm wasused. After the growth, crystals were cooleddown to room temperature at a constant rate of30ºC/h. The grown crystals were colorless, anddid not show any major influence of the ambienti.e. air or oxygen. However, the cracking ofcrystals, as shown in Fig.10, was frequentlyobserved, and was a matter of concern. In orderto investigate this problem, thermal expansionmeasurements were carried out on the growncrystals [14]. Sample for these measurements

Fig. 9: Photographs of NaBi(WO4)

2 crystals grown from

‘A’: sintered charge under 6°C/cm gradient, ‘B’: sinteredcharge and ‘C’: re-crystallized charge under 60°C/cmgradient.



was prepared by carefully cutting the crystal intoa rectangular piece of dimension 6.5mm x 4.5mmx 4.0mm having faces parallel to (100), (010)and (001) crystallographic planes. Measurementswere carried out using a dilatometer (model-TMA/92 Setaram, France) with a silica probe,in the temperature range 30-1000°C employinga heating rate of 10°C/min in high pure Arambient. The results of experiment show thatexpansion coefficient is quite high in <001>direction compared to that in other two directionsi.e. <100> and <010>. Therefore <001> directionwas selected for the growth in order to allowmaximum expansion in the growth direction andthus keeping isotropic expansion directions in therotation plane. The cracking was successfullyavoided in this manner.

(v) LBO/LGBO

Lithium tetra borate and lithium gadolinium triborate have elements like Li, B, Gd that havehigh neutron capture cross-sections and hencecan be effectively used in neutron detection anddosimetry. Being low-z materials these are alsogamma transparent which is a crucial propertyfor materials to be used as a neutron detector inhigh gamma background, like reactors. Thesematerials are mostly grown by the CZ method.

LBO has a tendency to go into a glassy phaseduring the cooling which limits its growth rate.

To avoid the glassy phase a very slow pull ratehas to be employed (typically 0.2-0.5 mm/h)therefore to grow a 20 mm diameter and 20 mmlength crystal it takes about a week. Anothergrowth related problem in the case of LBO isthe core formation which is due to decompositionand selective evaporation of LBO at elevatedtemperatures.

LBO crystals doped with Cu and Ag were alsogrown by the Cz method. The doped LBO crystalis an excellent dosimeteric material (thermallystimulated as well as optically stimulatedluminescence dosimetery) [3]. Typicalphotographs of doped and undoped crystals areshown in Fig.11.

LGBO is a new material and has potential to beused as a scintillation detector for neutrons whenactivated with Ce. Its growth is relatively easycompared to LBO. But due to the presence ofcleavage planes, cracking in a large size crystalis still an unresolved problem. We have growncrack-free transparent crystal having 12 mmdiameter and 40 mm length, as shown in Fig. 12.Research is going on in order to increase thedimensions further

Laser Crystals

Oxide materials like YAG, Al2O

3, NYW, NGW

KYW, KGW are a few of the excellent laser

Fig. 10: Photograph of BaWO4 crystals

showing cracks.Fig. 11: Photographs of LBO singlecrystals (as-grown).

Fig. 12: Photograph of as-grown single crystal ofLi

6Gd(BO

3)

3.



hosts. Here in crystal technology lab we havegrown single crystals of NYW, NGW doped withNd and Yb, respectively. These crystals aregrown by the Czochralski techniques (CZ).Growth details and problem encountered duringthe growth of these crystals are as follows:

(i) NaY(WO4)

2 (NYW)

Single crystals of NYW are grown by the CZtechnique. The occurrence of compositionalchanges during the growth of NYW crystalscauses instabilities in the mass growth rate andincreases the vulnerability of these crystalstowards development of cracks. Analysis ofdifferent regions of grown crystals and postgrowth residual charges revealed the presenceof excess Y

2O

3 in the upper portion of ingots

and excess of Na2O in the residual charge, in

the form of binary compounds of sodiumtungstate. Phase purification through re-crystallization, as achieved in another doubletungstate crystal NaBi(WO

4)

2, was not effective

in NYW, due to a lack of segregation of allforeign components into the melt anddecomposition of the material.

The phase diagram of the Na2WO

4-Y

2(WO

4)

3

pseudo-binary system shows that there exists acongruent melting composition correspondingto a 1:1 molar ratio in this systems. However,crystal growth from a congruent meltingcomposition did not yield a good quality crystaland suffered from the above mentionedproblems. In our recent work on this material,several off-stoichiometric compositions wereprepared along with a stoichiometric compoundusing a solid-state route and characterized fortheir thermal and structural behavior using DTAand XRD measurements. Based on results ofthis study, a suitable composition rich in theY

2(WO

4)

3 for the growth of NYW crystal was

suggested [15]. Furthermore, crystal growthexperiments were carried out on NYW by the

Czochralski technique employing the startingcharge rich in Y

2(WO

4)

3 that rectified all the

growth related problems except those which mayarise probably due to the anisotropy in thermalproperties of the crystal. A polished disc fromthe grown crystal (undoped) is shown in Fig.13which shows a good transparency.

(ii) NaGd(WO4)

2 (NGW)

Yb doped NaGd(WO4)

2 single crystals are

important for applications in high power tunedlaser sources in the near-infrared region due totheir relatively smaller stock-shifts and broadabsorption/emission bands. Single crystals of 4%Yb doped NaGd(WO

4)

2 (NGW) were grown

from stoichiometric charges using theCzochralski technique under normal ambientconditions. The grown crystals were transparentwith a slight greenish tinge. The coloration ofthe grown crystals was increased when the samecharge was used in the following growth runsby replenishing the drawn amount with anequivalent amount of the fresh charge. Aftermany growth run the leftover charge wasanalyzed and it was found that it was rich inforeign phases like sodium tungstates andNa

5Gd(WO

4)

4. Annealing studies revealed that

the oxygen related defects were the main causebehind the coloration. Based on these feedbacksa recrystalized charge was used that yielded less

Fig. 13: Photograph of as-grown single crystal ofNaY(WO

4)

2 (left) and polished disc.



Transmission and absorption spectra wererecorded at room temperatures employing aspectrophotometer in the 200-1100 nm range.The absorption spectrum of Yb was fitted in multiGaussian peaks centered around 936, 954, 964,975, 981, 996 and 1010 nm that matched wellwith the theoretically predicted values [16]. Thisresult also confirmed the quasi three level natureof the Yb 2F-

7/2 → 2F-

5/2 system.

Optical crystals

Fluoride optical crystals CaF2, BaF

2, LiF are

grown using the vacuum Bridgman furnaces. Agraphite heater is used for the resistive heatingof graphite crucibles containing the material.Lowering mechanism is coupled with the crucibleusing a Wilson seal. All the systems includinggrowth chamber, electrodes, pulling mechanismare cooled using a complex heat exchangermechanism.

The growth of these materials is relatively easythough there are few problems which had to beconquered. Even after high vacuum of the orderof 10-5 mbar, contamination of oxygen during the

growth is the most serious problem in growinghigh quality device grade fluoride crystals forapplications in optics. The oxygen scavenger likePbF

2 that does not affect other optical properties

of crystals is used to minimize the oxidation ofmaterials during the growth. Dehydration andproper fluorination are also necessary steps togrow high quality crystals. Fluorination of thematerial is done in a special furnace which isresistant to HF. Typical photograph of 80 mmdiameter LiF (as-grown) and a 50 mm polisheddisc of CaF

2 is shown in Fig.15.

Fig. 14: Photographs of as-grown crystals and polisheddisc and cubes of NaGd(WO

4)

2.

Fig. 15: Photographs of (a) LiF as-grown crystal and(b) polished disc of CaF

2.

colored crystals. Crystal growth experimentswith different ambient are also planned in orderto minimize the coloration. Photographs of as-grown crystals and polished disc and cubes areshown in Fig. 14.

Crystal growth and characterization facilitiesat CTS

Under the single roof of the crystal technologybuilding, there are several sophisticated crystalgrowth facilities equipped with advancedCzochralski crystal pullers and indigenouslydeveloped high temperature vacuum Bridgmanfurnaces in the clean-room environments.Photograph having panoramic view ofCzochralski pullers and vacuum furnaces areshown in Fig.16 and Fig.17, respectively. Inaddition, there are various instruments forcharacterization of grown crystals includingpowder X-ray diffraction instrument, X-rayfluorescence instrument, photoluminescencespectrometer (200-900 nm), differential thermal



analyzer (50-1750ºC), thermo-mechanicalanalyzer (50-2400ºC), in-house developedgamma-ray spectrometer for scintillation testingand thermoluminescence reader andspectrometers. Results of these experiments areused as feedbacks in successive growth runs todevelop the device-grade crystals.

References

1. Robert Hofstadter, Phys. Rev. 75 (1949)796-810.

2. S.E. Derenzo, M.J. Weber, E. Bourret-Courchesne, M.K. Klintenberg, Nucl.Instr. and Meth. A 505 (2003) 111–117.

3. Babita Tiwari, N.S. Rawat, D.G. Desai,S.G. Singh, M. Tyagi, P. Ratna, S.C.Gadkari, M.S. Kulkarni, J. Lumin. 130(2010) 2076 – 2083.

4. S.G. Singh, Mohit Tyagi, A.K. Singh, S.C.Gadkari, Nuclear Instrum. Methods InPhys. Res. A 621 (2010) 111-115.

5. Alexander A. Kaminskii, Phys. Stat. Sol.(a) 200 (2003) 215–296.

6. www.globalopticsuk.com

7. J.C. Brice, “The Growth of Crystalsfrom Liquids”, North-Holland PublishingCo., 1973.

8. J. Czochralski, Z. Phys. Chem. 92(1918) 219-221.

9. P.W. Bridgman, Proc. Amer. Acad. ArtsSci. 60 (1925) 303-383.

10. K. Chennakesavulu, S.G. Singh, A.K.Singh, S.C. Gadkari, Proc. NSGDSC,BARC, (2009), India.

11. K. Nitsch, M. Nikl, S. Ganschaw, P.Reiche, R. Uecker, J. Crystal Growth,165 (1996) 163-165.

12. Mohit Tyagi, S.G. Singh, A.K. Singh, S.C.Gadkari, Phys. Status Solidi A 207 (2010)1802-1807.

13. S. G. Singh, M. Tyagi, A. K. Singh, andSangeeta, Cryst. Res. Technol. 45 (2010),18 – 24.

14. A.K. Chauhan, J. Crystal Growth, 254(2003) 418-422.

15. R.G. Salunke, S.G. Singh, A.K. Singh, D.G.Desai, S.W. Gosavi, A.K. Chauhan, S.C.Gadkari. American Institute of Phys.:Conf. Proc. 1313 PEFM (2010) 397.

16. S.G. Singh, M. Tyagi, D.G. Desai, A.K.Singh and S.C. Gadkari, 14th NationalSeminar on Crystal Growth, NSCG-XIV,VIT University, Vellore (2010).

Fig. 16: Photograph of Czochralski crystal puller lab. Fig. 17: Photograph of vacuum Bridgman furnace lab.



Heavy Liquid Metal Technology Development

A. Borgohain, N.K. Maheshwari, P.K.Vijayan and R.K. Sinha

Reactor Design & Development Group

A b s t r a c t

Liquid metal is increasingly getting more attention as the coolant for advanced reactor systems.This article deals with the activities performed on coolant technology for high temperature reactor applications.

A lead bismuth natural circulation loop has been set up, for thermal hydraulics, instrument development and

material related studies relevant to the Compact High Temperature Reactor.

I n t r o d u c t i o n

Many reactor designs based on heavy liquidmetal as coolant have been envisaged by variouscountries for high temperature process heatapplications such as hydrogen production bythermo-chemical processes. Heavy liquid metalsystems are excellent spallation targets forAccelerator Driven Systems (ADS). Liquidmetal especially lead-lithium is also consideredfor the blanket in the InternationalThermonuclear Experimental Reactor (ITER).Natural circulation of liquid metal coolant is beingconsidered as the normal core cooling mode insome advanced reactor designs including theLead cooled Fast Reactors (LFR) beingdeveloped by Generation IV International Forum(GIF) [1]. Presently, technology developmentfor a small power Compact High TemperatureReactor (CHTR) capable of supplying hightemperature process heat at 1273K is beingcarried out in BARC.

Attributes of Lead Alloys as a ReactorCoolant

Lead and lead alloys have extremely high boilingtemperature at atmospheric pressure (1943-2023K). This facilitates an ambient pressure

primary system- a safety hall mark of liquidmetal cooled reactors, which essentiallyprecludes the loss of coolant accident initiator.Very high coolant boiling point precludes boilinginduced voiding. This holds when the propertiesof the lead alloys are exploited to raise core outlettemperature in a range (1173-1273K) suitablefor hydrogen production missions. This marginallows room for passive safety strategies to work.Lead and lead alloys are used as a coolantbecause they do not react vigorously with airand water. Neutronicallly, lead (and lead alloysgenerally) exhibit low neutron absorption and lowneutron slowing down power. Lead alloys areexcellent gamma ray shields. Activation of thecoolant is significant for Pb-Bi alloy and issignificantly less for pure lead. The long-termactivation which might affect decommissioningwaste streams exceeds that of sodium. Theirability to corrode iron-based structural materialsrequires a regime of rigorous coolant chemistrycontrol to maintain protective surface layers onthe structural members.

R&D Scope and Challenges

Lead alloy cooled thermal reactor concepts willrequire several years of “technology focused”R & D in order to establish some of the



fundamental data and understanding requiredbeyond the pre-conceptual design. Research anddevelopment required for reactor design anddevelopment to use lead alloy as a coolant in thefield of analytical chemistry and engineeringapplication is listed below and it would later befollowed by more extensive development toactually bring a product to use.

Material compatibility at high temperature

In the CHTR [2], beryllia and graphite areextensively used as reactor core materials. Thecompatibility of lead alloy coolant with thesematerials is required to be assessed.Furthermore, issues have been raised concerningthe possibility of leaching out of alloying agentsfrom structural materials containing very hotflowing lead and lead-bismuth. The compatibilityof materials are first to be assessed separatelyand then in combinations. The coolant additivesor high temperature coatings may result inacceptable material compatibility at hightemperature and is required to be assessed fromcorrosion chemistry and integrity point of view.

Oxygen control and measurement

The amount of dissolved oxygen in liquid leadalloys should not increase beyond a limit to avoidthe contamination of the liquid system by leadand bismuth oxides and should not be less than acertain limit which may cause dissolution ofalloying element of the structural material.Therefore the oxygen level must be constantlymonitored and kept within a certain range [3].The development of robust oxygen sensor foronline measurement of dissolved oxygen is alsoan important requirement for safe operation ofthe system.

Solid impurities control

Impurities enter the coolant during reactor

operation by corrosion of metal surfaces,diffusion of metal constituents through the metaland via maintenance operations involving accessinside the system. The monitoring of theimpurities is essential for online detection up toa very low level.

Coolant activation

In lead bismuth eutectic, the generation ofradioactive polonium (Po-210, t1/2

=138.3 days)resulting from an (n, γ) reaction with 209Bi andsubsequent beta-decay is an issue. Polonium-210 is very toxic and troublesome in the eventof leakage owing to its tendency to scatterthrough the available volume. The methods foreffective removal of polonium fromcontaminated surfaces and from the atmosphereare required to be developed and tested.

Thermal hydraulics

Systematic studies on the degradation of heattransfer due to oxide formation on heat transfersurface are needed for design of reactor coolantcircuit and heat exchangers. The studies onbehaviour of liquid metal during naturalcirculation under various transients are rare. For3-D thermal hydraulic analysis of reactor systemsinvolving natural circulation, CFD codes arefound to be very useful. But proper validation ofthe codes for liquid metal application is essentialbefore using it for the actual system analysis.Another area of importance is the coupling ofthe system codes with 3-D CFD codes. Thiswill help in coupled 1-D and 3-D analysis of thewhole reactor system accurately andeconomically.

The liquid metal systems using lead (Pb) or lead-bismuth eutectic (LBE) require measurementtechnologies especially adapted to them.Instruments for measurement of pressure,pressure drop and low flow rate for high



temperature application are required to bedeveloped.

Activities on Lead Bismuth CoolantTechnology Development

Lead-Bismuth test loop

A lead-bismuth natural circulation loop has beenset up, for thermal hydraulics, instrumentdevelopment and material related studiesrelevant to CHTR. Steady state and transientstudies are carried out in the loop. Fig. 1 showsthe isometric view of the loop and a photograph.More details of the loop and experimental studiescan be found in [4]. The loop mainly consists ofa heated section, air heat exchanger, valves,various tanks and argon gas control system. Allthe components and piping are made of SS316L.The LBE ingots are melted in a melt tank andthen transferred to the sump tank. The LBEcoolant in the sump tank is then pressurized byargon gas system. Due to pressurization moltenLBE flows into the loop and subsequently fillsup the loop. After filling, the loop was isolatedfrom the sump tank by a valve. Natural circulationof the coolant takes place in the loop due toheating of the coolant in the heated section andcooling in the heat exchanger. Air is used as thesecondary side coolant in the heat exchanger.After losing heat in the heat exchanger LBEenters the heated section through 15mm NominalBore (NB) pipeline.

Oxygen measurement and control

An oxygen sensor was developed to measuredissolved oxygen level in LBE. The oxygensensor consists of a one-end closed YSZ tube.Bismuth and Bismuth oxide is used as referenceelectrode. The sensor has been tested in aseparate test set up [5] before installation in theloop. Fig. 2 shows the oxygen sensor used in the

loop. Fig. 3 shows the variation of emf of thesensor during operation of the loop.

Fig. 3: Variation of temperature and EMF with time

Fig. 1: 3D view of the main loop and photograph

Fig. 2: In-house developed oxygen sensor



Material testing in Lead-Bismuthenvironment

Material compatibility related studies with leadbismuth coolant at high temperature are inprogress. Fig. 4 shows the micrograph ofgraphite sample tested at 1123K in LBE mediumfor 500 hrs. No significant corrosion orpenetration of LBE into the graphite material isobserved after the test. Material compatibilitystudies on stainless steel and graphite in LBEmedium have also been carried out by otherresearchers [6, 7].

Fig. 4: Micrograph of graphite after 500 hrs operation inLBE at 1123K

Computer code development and its validation

A computer code, LeBENC (Lead BismuthEutectic Natural Circulation) is developed tostudy the steady state and transient behaviourof liquid metal natural circulation in a closed loop.The code can handle uniform and non-uniformdiameter piping in the loop, different workingfluids (water and LBE) and accounts for axialconduction in the fluid and pipe wall. The detailsof the code can be found in [3]. The code wasfirst validated [8] with experimental data onnatural circulation in water.

Validation in the Lead-Bismuth loop

Steady state and transient experiments werecarried out. In transient studies start up ofthe natural circulation, loss of heat sink andloss of heater power were studied. For all theexperiments, the computer code was run with

the same inputs as initial conditions in the testloop and results obtained were plotted forcomparison. Fig. 5 shows the steady state resultsat various heater powers and the comparison ofthe prediction of LeBENC code. Fig. 6 shows acomparison of theoretical results withexperimental data for start up of naturalcirculation from stagnant condition with heaterpower of 1800W in the loop.

Fig. 5: Steady state natural circulation results at differentpower levels

Fig. 6: Start-up of the loop from stagnation condition,heater power 1800W

CFD analysis

Computational Fluid Dynamics (CFD) is usedfor the 3-D thermal hydraulic analysis related toCHTR. PHOENICS, a general purpose CFD



code is used for the analysis. The code has beenassessed for liquid metal heat transfer analysis[9]. Based on the assessment 3-D thermalhydraulic analysis of the CHTR core [2] iscarried out. The full-scale reactor core has beenmodelled in PHOENICS. Natural circulationof the coolant is modelled with Boussinesqapproximation. Fig.7 shows the 3D temperaturedistribution in the core for normal operatingcondition. The average flow velocity of thecoolant in the fuel tube is found to be 3.3m/min.CFD analysis on the lead bismuth loop has alsobeen carried out. Fig. 8 shows the steady state3D temperature distribution of the loop withheater power 2000W.

Fig. 7: Temperature Distribution in the CHTR core.

Fig. 8: Temperature distribution in the loop,heater power 2000W.

Concluding Remarks

Steady state and transient studies have beencarried out in the Lead-Bismuth loop. Sensorfor online measurement of dissolved oxygen inLBE at high temperature was developed andtested in the loop. A computer code is developedand results are compared with the experimentaldata. The development of instruments for liquidmetal application and material testing are inprogress.

References

1. Annual Report-GIF, 2009, http://www.gen-4 . o r g / P D F s / G I F - 2 0 0 9 - A n n u a l -Report.pdf.

2. I. V. Dulera and R. K. Sinha, 2008, “HighTemperature Reactor”, J. Nucl.Materials, 383 1-2, 15, 183-188.

3. X. Wu, J. Ma, Y. Jiang, B. Fu, W. Hang,J. Zhang, and N. Li, 2006,“Instrumentation of YSZ Oxygen SensorClibration in Lquid Lad-Bsmuth Etectic”,IEEexplorer, accessed at: http://i e e e x p l o r e . i e e e . o r g / s t a m pstamp.jsp?tp=&arnumber=1464945&userType=inst.

4. A. Borgohain, B. K Jaiswal, N. K.Maheshwari, P. K. Vijayan, D. Saha andR. K. Sinha, “Natural Circulation Studiesin a Lead Bismuth Eutectic Loop”, J.Nucl. Progress (accepted for publication).

5. A. Borgohain, N. K. Maheshwari, P. K.Vijayan, D. Saha and R. K. Sinha, 2008,“Development of High TemperatureOxygen Sensor for Lead BismuthEutectic”, Proc. Discussion meet onElectro Analytical Techniques & theirapplications”, ISEAC Munnar, Kerala, Feb25-28.



6. C.M. Das and R. Fotedar, “Experienceson Lead-Bismuth Loops”, 2008, Workshopon Steel and Fabrication Technologies forFusion Programme (WSFT-08), Institutefor Plasma Research, Ahmedabad.

7. A. K. Sengupta, R. K. Bhagat, A. Laik,G.B. Kale, T. Jarvis, S. Majumdar and H.S.Kamath’ 2006, “Out of Pile ChemicalCompatibility of Pb-Bi Eutectic Alloy withGaphite”, International Journal forMaterials Research, 97, 834-837.

8. B.K. Jaiswal, P.K. Vijayan, N. K.Maheshwari, A. Borgohain, 2008,

“Development of a Computer Code toStudy the Steady State and TransientBehaviour of Liquid Metal NaturalCirculation Loop”, 19th National and 8thISHMT-ASME heat and mass transferconference, JNTU Hyderabad, India.

9. A. Borgohain, N.K. Maheshwari, P.K.Vijayan, D. Saha and R. K. Sinha, 2008,“Heat Transfer Studies on Lead-BismuthEutectic Flows in Circular Tubes”,Proceedings of 16th InternationalConference on Nuclear Engineering(ICONE), May 11"15, Orlando Florida.



Indigenous Development of Silicon PINPhotodiodes Using

a 4" Integrated Circuit Processing Facility

Anita Topkar, Arvind Singh, Bharti Aggarwal and C.K. Pithawa

Electronics Division

and

A.S. Rawat

Laser & Plasma Technology Division

A b s t r a c t

A wide range of single element silicon PIN photodiodes and 16-element PIN photodiode linear arrays havebeen indigenously developed using the 4" integrated circuit processing facility of Bharat Electronics Limited,

Bangalore. The photodiodes show low dark currents and good optical performance in the visible range. The

overview of this technology development activity is presented in this article.


Silicon PIN photodiodes feature high speed, lowseries resistance, low dark current and lowjunction capacitance resulting in low noise andfast response time of the order of a few ns.Compared to photomultiplier tubes, siliconphotodiodes offer specific advantages such aslow operating voltage (<100V), high quantumefficiency, insensitivity to magnetic fields, andsmall sizes. As a result, PIN photodiodes arenow being used extensively in wide range ofapplications involving radiation monitoring,nuclear physics (for medium-energy chargedparticle detection) and particle physicsexperiments (electromagnetic calorimeters).These devices are widely used in laser basedmetrology applications (measurements ofdiameter, surface roughness, projectile velocity,distance and vibration) and beam parametermeasurements (power, temporal profile, pulseenergy). As scintillation detectors, major

applications of PIN photodiodes are in the arenaof security systems such as X-ray baggagescanning and cargo scanning, industrialtomography and medical imaging systems. Thetechnology for the production of PIN photodiodesfor the above mentioned applications was notavailable in our country resulting in dependencyupon the foreign commercial suppliers for thesedevices. Therefore, indigenous development ofthese devices was taken up.

Fabrication Technology

Considering the range of applications of siliconphotodiodes as mentioned above, indigenoustechnology development of silicon PINphotodiodes has been carried out using a 4"processing line of Bharat Electronics Limited(BEL), Bangalore. The silicon photodiodes havebeen fabricated using silicon IC fabricationtechnology. A planar process which combinesoxide passivation with ion implantation gives



better device properties compared to diffusedjunction devices, and hence this process has beenadopted for fabrication of the photodiodes. Oxidepassivation over the surface is useful forreduction of leakage currents whereas ionimplantation allows accurate control of junctions.N Type, <111>, 4-6 kΩ-cm high purity siliconwafers of 300μm thickness are used as startingmaterial and the subsequent process steps havebeen optimized so that the generation of defectsis minimized. The front P+ region has beenobtained by boron ion implantation whilephosphorous has been used to obtain a N+ regionat the back. Several process steps have beenincorporated to reduce the dark current. Thebreakdown voltage has been tuned to enableoperation in full depletion mode so as to get aminimum terminal capacitance. Silicon dioxidehas been used as an anti-reflection layer overthe active region and it has been tuned for thewave length of CsI scintillator. Initially, processruns have been carried out using a test-mask tooptimize the required electrical and opticalperformance. Subsequent to processdevelopment, another mask was designed toincorporate different types of photodiodes. Thisdesign incorporated photodiodes with sensitivearea ranging from 0.5mm2-150mm2, quadrantdetectors and 16-element linear arrays ofphotodiodes. The main fabrication steps used forthe fabrication of photodiodes are given below:

• Initial oxidation• P+ lithography• Screen oxidation• P+ implant of boron• P+ drive-in and anneal• Back N+ implant of phosphorous, drive–in

and anneal• Contact opening, metallization and

passivation on the front side• Dicing and packagingSubsequent to wafer fabrication, the photodiodes

are packaged in different types of packages suchas metal TO (Transistor Outline) packages withglass window or flat package using ceramicsubstrates. The packages were customdeveloped at BEL, Bangalore.

Fig.1 shows the photograph of fabricated waferincorporating various types of photodiodes.

Fig. 1: Fabricated wafer showing various types of PINphotodiodes

Performance of Photodiodes

The characterization of the photodiodes has beencarried out by measuring the dark currents andreverse capacitance at different bias voltageusing automated measurement setups.The typical dark currents at different bias voltagesfor a number of photodiodes of area 100mm2

are shown in Fig. 2. The dark currents at voltagesexceeding full depletion voltage are about3-5nA/cm2. The typical capacitance vsvoltage characteristics for photodiode with areaof 100mm2 is as shown in Fig. 3. As can be seen,the capacitance at full depletion voltage is about45 pF/cm2.



The optical characterization has been carriedout by measuring the responsivity at differentwave lengths of light in the visible range. Theresponsivity has been measured at 543nm,632nm and 940nm wavelengths using laser/LED. During these measurements, the opticalpower of incident light on the photodiode wasmeasured using a power meter. The currentgenerated due the incident photons in thephotodiode was measured using a transimpedance amplifier. The diodes were used inphotoconductive mode and the output voltagewas measured to calculate the photocurrent.

The optical response of the photodiodes wascompared with commercially availablephotodiodes of similar specifications. The spatialuniformity of the optical response and linearityat different input optical powers was alsomeasured.

The optical performance of the photodiodes hasbeen observed to be as good as that of importedcommercial photodiodes (Fig.4).

Fig. 2: Typical dark current vs voltage characteristic forphotodiodes of area 100mm2

Fig. 3: Typical capacitance vs voltage characteristic ofphotodiode of area 100mm2

Fig. 4: Responsivity of photodiodes at differentwavelengths in the visible range

The spectroscopic performance of indigenouslydeveloped CsI-photodiode detector assembly fordifferent gamma energies was investigated bycoupling the photodiode to CsI scintillator. TheCsI scintilator was grown at TPD, BARC. ACsI scintillator with dimensions of 10x10x15 mm3

was coupled to a photodiode of 10mmx10mmgeometry for carrying out these measurements.Fig. 5 shows the response of CsI:PIN photodiodedetector assembly for different gamma-rayenergies over a range of 511keV to 1275keV[1].

The CsI-photodiode detector shows a goodlinearity in the 511 keV -1275 keV range. Thedetector shows energy resolution of about 16%at energy of 662 keV.



PIN photodiode with activearea of 0.2 mm2 (0.5mmdia.) and with a mini-lensewindow

PIN photodiode with activearea of 0.78 mm2 (1mmdia.) and with a mini-lensewindow

Quadrant detector witheach element of 1.3mm x1.3mm, 0.1mm gap and witha glass window

PIN photodiode with activearea of 25 mm2 and with aglass window

Fig. 5: Response of CsI:PIN photodiode detectorassembly for different gamma-ray energies [1]

Quadrant detector with totalactive area of 150/50mm2

and with a glass window

PIN photodiode with activearea of 50/100mm2 and witha glass window

PIN photodiode with asquare geometry, with activearea of 100mm2 and with aglass window

Element geometry of1.57mm x1.22 mm andpitch of 1.57mm

Element geometry of2.5 mm x 2.15mm andpitch of 2.5mm

Element geometry of10 mm x 0.8mm andpitch of 1.3 mm

Types of Photodiodes Developed

Various types of photodiodes which have beendeveloped include single element diodes,quadrant detectors and 16-element linear arrays.Some of these photodiodes are shown below:

Summary

Various types of PIN photodiodes have beenindigenously developed using the 4" integratedprocessing facility of BEL, Bangalore andtheir performance has been evaluated.The photodiodes have been observed to have

16-element PIN photodiode linear arraysfor X-ray imaging with scintillator



performance comparable to that of commercialphotodiodes. As this technology developmentwas carried out using the foundry facility of BEL,the photodiodes will be commercially availablefrom BEL, Bangalore. Using the technologydeveloped, it would be also possible to tune thespecifications such as geometry, types ofsegmentation, spectral response, etc., for specificapplications.

Acknowledgement

The authors would like to thank Mr. G.P.Srivastava, Director E&IG, Dr L. M. Gantayet,Director, BTDG, Mr. R.K Patil, AssociateDirector (C), E&IG and Dr A.K. Das, Head,

L&PTD for their support in carrying out thiswork. The contribution of Dr S.C. Gadkari, TPDand Mr. S.G. Singh, TPD, BARC in investigatingthe gamma response of CsI-photodiode detectoris acknowledged.

References

1. S.G. Singh, Arvind Singh, Anita Topkar,S.C. Gadkari, “Performance ofindigenously developed CsI(Tl)-photodiode detector for gamma-rayspectroscopy”, presented in 55th DAE-Solid State Physics Symposium(DAE-SSPS 2010), Paper in press in AIPConference Proceedings.



Development of Room Temperature NH3 GasSensors based on Ultrathin SnO2 Films

Sipra Choudhury, C.A. Betty, K.G. Girija

Chemistry Division

A b s t r a c t

Ultrathin SnO2 film deposited by Langmuir–Blodgett technique showed high sensitivity (< 3 ppm) for NH

3 gas

at room temperature with fast response (<1 min) and 90% recovery within half-an-hour. The sensitivity remained

the same and was reproducible even after one year indicating the long term stability of the sensor. The sensorwas highly specific to NH

3 in presence of the other reducing gases - H

2S, SO

2, CO, H

2 and CH

4. In the presence

of H2S and SO

2, the film

conductivity increased whereas it decreased with ammonia. There was no response

with other reducing gases.


The current era of high technology and advancedindustry has produced an incredible rise in livingstandards. However, this has also beenaccompanied by a variety of seriousenvironmental problems, for example, theatmospheric release of various chemicalpollutants, including NO

x, SO

x, HCl, NH

3, CO

2,

volatile organic compounds (VOCs) andfluorocarbons from industries, automobiles, andhomes. These polluting gases result in seriousglobal environmental issues, such as acid rain,greenhouse effect, sick house syndrome andozone depletion. To prevent or minimize thedamage caused by atmospheric pollution,monitoring and controlling systems are neededthat can rapidly and reliably detect and quantifypollution sources within the range of theregulating standard values. Till now, air pollutantmeasurements have been carried out withanalytical instruments using optical spectroscopy,gas chromatography or mass spectrometry.

Although these instruments can give a preciseanalysis, they are time-consuming, expensive, andcan seldom be used in real-time in the field.Therefore, a gas sensor that is compact androbust with versatile applications and low cost,could be an equally effective or better alternative.

Gas sensors for detecting air pollutants mustbe able to operate in a stable manner underdeleterious conditions, including chemicaland / or thermal attack. Therefore, solid-stategas sensors would appear to be the mostappropriate ones in terms of their practicalrobustness. There are several solid-stategas sensors currently available for gases suchas O2

, H2O, H

2S, LPG at relatively high

concentrations [1]. However, the range ofair pollutant concentrations that is to be detectedreaches as low as few ppm in combustionexhaust control or indoor monitoring andfew ppb in atmospheric environmentalmonitoring. Therefore, the development of moresensitive and selective gas sensors than theconventional ones is still required. Over the past



few decades solid state gas sensors based onpolycrystalline SnO

2 thin films have become

predominant for gas alarms in domestic,commercial and industrial premises. Thesesensors are usually operated at temperature>200oC to achieve reversibility and fast responseand they are mainly used for H

2S, CO and H

2

sensing. Sensors operated at high temperature,though specific to a particular gas at thattemperature, suffer from shorter life-time andhigh thermal budget. Besides, in an explosiveenvironment, the high-temperature operation ofthese oxide sensors is not favorable. Evidently,room temperature operation is preferable,however, in the case of polycrystalline thin filmsthe bottleneck for room temperature operationlies in the dominant grain boundary barrierresistance (Schottky diode). This can be readilyovercome by exploiting nano-scale structuresof SnO

2. Very small grain size and high surface-

to-volume ratio associated with thenanocrystallites allow the sensors to be operatedin the most sensitive, grain-controlled mode,having a completely depleted space chargeregion.

Depending on the degree ofnonstoichiometry (SnO

2-x) of the

film, exposure to oxygen leadsto some of the oxygen beingadsorbed at surface defects. Theadsorption passivates the surfacevacancies, drawing electronsfrom the bulk and localizing themon the chemisorbed / ionosorbedoxygen, thereby creating a spacecharge region of positivelycharged ions near the surface.The effect of grain size and grainboundary barrier on carrierdensity modulation (Δn

e) is

schematically shown in Fig. 1(n

e vs. film thickness l), for micro

and nanogranular films. The two cases are scaledusing Debye length L

D in SnO

2 film for a given

temperature. Fig. 1(i) and (ii) (upper part) showthe top view of the polycrystalline interconnectedmicrograins and nanograins respectively withoutany amorphous phase in between. The distancebetween the grain boundaries to the dotted lineindicates the Debye layer thickness L

D created

by the charge transfer with the surface adsorbedspecies. With the film thicknesses l > 2L

D, band

bending due to oxygen chemisorptions exists onlynear the surface [2] (the band diagram is shownlater in Fig.6). The corresponding electron densityplot (lower part of Fig. 1 (i)) shows that there isno effect on the bulk electron density except onthe grain boundary due to the adsorbed species.In contrast, the effect of adsorption onnanostructures ( l < 2L

D) is to deplete the

nanograin completely of the charge carriers (Fig.1(ii) upper part). This in turn changes the locationof the Fermi level (which is proportional to Δn

e)

within the band gap of the nanostructure (Fig. 1(ii), right bottom panel) causing an appreciableconductance drop. In order to exploit the above

Fig.1: Schematic diagrams of space charge formation at the grainboundaries (upper part) and carrier density modulation (lower part) dueto surface adsorbed species (O-, O2-) on micro and nano granular film.The continuous lines (upper part) represent grain boundaries. L

D is the

Debye length, l is the grain size, ne is carrier density, Δn

e change in carrier

density. (+) indicates the charge on Sn atom inside the grain.



mentioned nanostructure properties in gas sensordesign we have deposited ultrathin films withL

D > l/2 by controlling the thickness of SnO

2

films using Langmuir–Blodgett technique. Gassensors fabricated using these ultrathin SnO

2

films have been successfully demonstrated fortheir room temperature response to NH

3

detection with high sensitivity and fast response.

Deposition of ultra thin SnO2 film

Ultrathin SnO2 film was deposited by Langmuir-

Blodgett (LB) technique, which provided highlyordered thin films of SnO

2. This technique of

depositing thin tin oxide film has advantages overother methods as it does not require vacuum andneeds only moderate temperature. It also

provides very good control of film thickness anduniformity of the ordered multilayers. MultilayerLB films of the anionic tin complexes withoctadecyl amine (ODA) deposited on varioussubstrates (Si, quartz and glass) weredecomposed at 600° C (2 hours) for desorptionof long hydrocarbon chain. In the presence ofoxygen, the tin ions formed oxides on thesubstrates (Fig. 2). SnO

2 films of 15-20 nm were

formed on various substrates from 120 layersof octadecyl (ODA) stannate LB film [3,4].Surface morphology in SEM examinationappeared to be non-porous (Fig. 2).

XRD pattern of the decomposed LB filmshowed peaks that are characteristic ofcassiterite structure of SnO

2 (Fig. 3(i)). Using

the Scherrer equation, analysis of <110> peakof cassiterite gave an approximate crystallitesize of 8 nm. In the XPS spectra, peaks wereobserved at 486.6 and 495 eV (Fig. 3(ii)a) withfull width at half-maximum of 1.6 eVrepresenting one oxidation state of Sn. Twooxygen peaks (Fig. 3(ii)b) are observed at 530.1eV and 532.2 eV. The lower binding energypeak is attributed to lattice oxygen in the SnO

2

crystal structure. The shoulder peak at higherbinding energy in O1s spectrum of the SnO

2

film corresponds to adsorbed oxygen at thesurface [3].

Fig. 2: Flow chart of the preparation of ultra thin SnO2

film from LB film precursor

Fig. 3: XRD pattern (i) and XPS spectra (ii) of Sn 3d (a) and O1s (b) of ultrathin SnO2 film.



Gas sensor fabrication

Inter-digitated gold electrodes were depositedby physical vapour deposition using shadowmask on the SnO

2 ultrathin film grown on quartz

substrate. An opaque glass chamber wasdesigned and fabricated for testing the sensorsat different ambients. The chamber was furtherwrapped with a dark adhesive tape to preventinterference from any stray light. The chamberhas inlet and outlet stopcocks for exposing it toambient air or for sweeping the carrier gas andan injection port for the specific gas to be tested.Fig. 4 shows the block diagram and thephotograph of the gas testing facility.

Testing and specificity studies

Known amounts of various gases (NH3, H

2S,

SO2, CO, H

2 and CH

4) from small canisters

were injected into the chamber without anycarrier gas flow, using gas tight syringes throughrubber septum. The chamber was kept closedcompletely till the sensor response saturated andthen the stop cocks were opened for recovery,by exposing to atmosphere. The roomtemperature sensitivity of the ultrathin SnO

2 films

towards ammonia gas was studied by measuringthe change in conductivity with time using anelectrometer interfaced to a personal computer.Typical time response to ammonia gas at roomtemperature is shown in Fig. 5(i). The responsetime was less than 1 min and 90% recoverytook place within half-an-hour. The lowestsensitivity observed (~ 3 ppm) is comparable tothe requirement for the air quality monitoring(50 ppm for 2 h exposure). Repeatedmeasurements were carried out on a singledevice over a period of 1 year and it showedthe same response to ammonia indicating the

stability and reproducibility of thesensor (Fig. 5(ii)). It was foundthat the response and recoverytimes were slower after one year.The reason for the slow recoveryafter a year could be due toexposure of the unpackagedsensor to ambient over a longtime

Gas sensing mechanism

As already mentioned thesurface of nonstoichiometricSnO

2-x chemisorbs oxygen

forming an electric double layer,through partial sharing ofconduction band electrons. Theresponse of this oxygen adsorbedsurface to different gasesdepends on their electrochemicalactivities. Strong reducing gaseswill uproot the adsorbed oxygen

Fig. 4: Block diagram and the photograph of the gas testing facility

Fig. 5: (i)Typical response (INH3

/Iair

) curve of SnO2 with ammonia

(ii) Sensitivity ((RNH3

-Rair

) x 100)/Rair

) plots of freshly prepared and oneyear old SnO

2 sensor.



layer for their own oxidation and in that processSnO

2-x surface gets back its shared band

electrons as well as conductivity. Presence ofstrong oxidizing gases on the other hand resultsin transformation of the double layer towardsstoichiometric SnO

2, decreasing the electrical

conductivity. Thus strongly reducing / oxidizinggases bring about irreversible changes in thesurface properties and it requires either air flowor proper heat treatment to gain back thesensing property. Interestingly, interaction ofammonia with the ultrathin film has caused a

decrease in conductivity as shown in Fig. 5. Thesensing mechanism of NH

3 is schematically

shown in Fig. 6. NH3 which is a mild reducing

gas, is a polar molecule containing partial positivecharge on its H atoms (Fig. 6). When NH

3 gas

is injected into the chamber, it settles on thesurface double layer through polar interaction(Fig. 6) and in this process reduces theconduction band electrons of SnO

2-x, thereby

reducing the conductivity. As the polar interactionis weak, NH

3 molecules undergo instant

detachment (disperse) from the double layerduring the recovery phase. This makes thesensor unique and specific to ammonia at roomtemperature.

Specificity

As for other gases like CO, CH4 and H

2 which

are not polar, they do not show any effect onthe SnO

2 film (Fig. 7(i)). In case of H

2S gas,

reduction reaction dominates on the SnO2

surface forming a new species making theresponse (increase in current) and recoveryslower. While testing with a gas mixture of NH

3

(10 ppm) and H2S (1 ppm) (Fig. 7(ii)) it was

observed that current decreased initially due toammonia gas (fast response, marked as 1)showing immediate response with ammonia.Subsequently, the current increased slowly due

Fig. 6: Schematic band diagram indicating the energylevels on the surface of SnO

2 thin film in presence of

surface adsorbed species and the target gas NH3; E

C, E

F,

EV, E

SS: energy levels of conduction band, Fermi level,

valence band and surface states respectively. (Xad)δ-

negatively charged surface adsorbed species.

Fig.7: (i) Response of the sensor with NH3, H

2, CO and O

2 gases

. (ii) Response with NH

3 and H

2S.

Circle indicates NH3 response with decrease in current.



to the presence of H2S gas (slow response).

After the saturation of current with H2S gas,

ammonia was injected again (marked as 2) andits characteristic response was observed. Evenin the presence of H

2S gas, subsequent ammonia

injection showed similar response (marked as3) as in the earlier case. These studies indicatedthe specificity of the SnO

2 sensor towards

ammonia gas even in the presence of otherreducing gas like H

2S. Table 1 summarizes the

specific properties of SnO2 based room

temperature NH3 sensor.

Conclusions

It has been demonstrated that ultra thin SnO2

films fabricated from the thermal decompositionof LB film precursor, exhibit room temperaturegas sensitivity comparable to that required forair quality monitoring. The sensor is specific toNH

3 gas at room temperature and shows fast

response and recovery without any carrier gasflow. The stability studies indicated that thesesensors are stable at least for a year with nosignificant change in sensitivity. The presentstudy also shows the applicability of thealternative LB technique for the formation of

ultrathin oxide film with controlled thickness,which is useful for many device applications.The entire fabrication process is cost effective.

Acknowledgements

Authors are thankful to Dr. D. Das, Head,Chemistry Division, BARC, for his constantencouragement, fruitful discussion andconstructive suggestions during the course ofthe work.

References

1. N. S. Ramgir, I. S. Mulla, K. P.Vijayamohanan, Sens.& Actuat, B,Chem. 107 (2005) 708-715.

2. W. Gopel, K.D. Schierbaum, Sens.&Actuat, B, Chem. 26 (1995) 1-12.

3. Sipra Choudhury, C. A. Betty, K.G. Girija,S. K. Kulshreshtha, Appl. Phys. Lett. 89(2006) 071914-16

4. Sipra Choudhury, C. A. Betty, K. G. Girija,Thin Solid Films 517 (2008) 923-928.

Property Value

Drift in base current 2-3 %

Sensitivity 10-14 % for 5 ppm of NH3

S=((RNH3

-Rair

)x 100)/Rair

Response time 40 sec (for 5 ppm NH3)

Recovery time (after opening of 30 mins for 90 % recovery

stopcocks, without any carrier

gas flow)

Reproducibility after a year Sensitivity intact

Response time 200 sec (5 ppm of NH3)

Recovery time 1 hr (5 ppm of NH3)

Specificity Specific to NH3 in presence of other

reducing gases (H2S, SO

2, CO, H

2,CH

4)

Table 1: Specifications of ultrathin SnO2 sensor

TECHNOLOGY DEVELOPMENT ARTICLEB A R C N E W S L E T T E R


Development of Online Radon and ThoronMonitoring Systems for Occupational and

General Environments

J.J. Gaware, B.K. Sahoo, B.K. Sapra, Y.S. Mayya

Radiological Physics and Advisory Division

Abstract

Online radon and thoron monitors have been developed using ZnS(Ag) detector for continuous monitoring ofconcentrations in occupational and general environments. Their performance has been tested successfully

both in laboratory and field conditions. Special features of these monitors include low cost, high sensitivity

and non-interference of humidity and trace gases. The capability of these radon monitors for networked radonmonitoring in U mines and in the U-tailings pond has been demonstrated. The thoron monitor is designed for

stack monitoring of thoron release in a thorium processing facility. Being highly sensitive, these monitors can

also be used for radon/thoron monitoring in dwellings, radon exhalation measurements, radon concentrationin water samples and thoron emission measurements from monazite sands in High Background Radiation

Areas.

Introduction

Unlike time-integrated monitoring of radon andthoron which is mainly limited to dosimetricapplications, continuous online monitoring yieldsinsight into spatio-temporal correlations, build-up in confined spaces, hourly variations inducedby pressure and temperature variations,atmospheric transport, extreme excursions,duration of specific highs and lows etc. Whilethe increased computational capabilities onenvironmental modeling have given rise togreater needs for real time data, thecorresponding developments in networking anddata transmissions have made it possible toachieve large scale simultaneousmeasurements. Such facilities are beingincreasingly developed as part of systems forearthquake predictions, in uranium mining,environmental monitoring and geophysicalresearch.

Apart from these general applications, monitoringradon concentrations in Uranium mining andthorium processing facilities is important toevolve effective strategies to reduce radiationdoses to occupational workers. With this in view,automatic radon and thoron monitors have beendeveloped as described below.

Description of systems

Online Radon Monitor

Traditionally, the Lucas scintillaton cell is usedfor one point sampling of radon (Lucas, 1957;Abbady et.al., 2004). The counting is carried outafter a delay of 3 hrs, allowing for the decayproducts to achieve radioactive equilibriumwith radon. The same Lucas cell may be usedfor continuous radon measurements withthe help of an algorithm for calculationof radon concentration for each sampling timeinterval. The algorithm accounts for the



fractions of radon decay products contributingto the total counts formed by radon in the currentinterval and in its preceding intervals. Thisinnovative algorithm for correlating the countswith the radon concentration has been developedin-house, based on the theoretical growth anddecay equations of radon decay products. Usingthis algorithm, two versions of radon monitorhave been developed. The portable version calledSRM (Scintillation Radon Monitor), utilizes aZnS:Ag based scintillation cell for measurementof alpha from radon and its decay products. Theother version named as ECAS (ElectrostaticCollection and Alpha Scintillation) is developedusing an electrostatic chamber for collection ofcharged decay products of radon on the ZnS:Agsurface. The details of these two versions aredescribed below.

Portable Radon Monitor - SRM

The schematic of the microprocessor based SRMand its photograph are shown in Figs.1a & 1brespectively. Radon is sampled into thescintillation cell (150 cc) through a “progenyfilter” and “thoron discriminator” eliminatingradon progenies and thoron. The thorondiscriminator based on “diffusion-time delay”does not allow the short lived thoron 220Rn (halflife 55.6 sec) to pass thorough. The alpha

scintillations from radon and its decay productsformed inside the cell are continuously countedfor a user-programmable counting period by thePMT and the associated counting electronics.The alpha counts obtained are processed by amicroprocessor unit as per the developedalgorithm to display the concentration of radon.

Considering the limitations on the range of thealpha particles (~6 cm), the dimensions of thescintillation cell were optimized to achieve highsensitivity (1.2 cph/Bqm-3) with lower detectorvolume (150 cc). The low detector volume,delivering very high sensitivity per unit activityof radon (6000 cph/Bq), is very useful formeasurements of mass exhalation and surfaceexhalation of radon from various naturallyoccurring radioactive materials

High Sensitivity Radon Monitor - ECAS

The low range of the alpha particles (~ 6 cm),makes it difficult to enhance the sensitivity ofthe SRM monitor just by increasing thedimensions (or volume) of the scintillation cell.Hence, an electrostatic collection technique forcharged decay products of radon, namely 218Po+

and 214Pb+ ions, on the ZnS:Ag scintillator hasbeen used. The schematic and the photographof ECAS are shown in Figs.2a & 2b respectively.As in SRM, the sampling of radon into the

Fig. 1a: Schematic diagram for Portable Radon Monitor(SRM)

Fig. 1b: Photograph of Portable Radon Monitor (SRM)



detector volume (1000 cc) is carried out bydiffusion through “progeny filter” and “thorondiscriminator” in succession. The electric fieldfor various detector geometries and dimensionswere modeled using commercial software andthe optimal field with this simple-to-fabricatecathode and anode design was obtained.Accordingly, an electrical potential of –2 KV isapplied to an aluminized mylar (12µm thickness)covering the ZnS:Ag scintillator coated on thecathode which is a solid perpex cylindrical blockwith a hemispherical head. The alphascintillations produced by 222Rn, 218Po and 214Poare detected by the PMT and the associatedcounting electronics. The alpha counts obtainedare processed by a microprocessor unit to displaythe concentration of radon.

Online Thoron Monitor

The indigenously developed microprocessorbased thoron monitor consists of two Lucasscintillation cells (LSCs) which are coupled to aseparate photomultiplier tube with associatedpulse preamplifier and scalar. Its schematicdiagram and photograph are shown in Figs.3a& 3b respectively. The LSC is a 2" dia and 3"height cell built in S.S. 316 material with inbuilttwo levels of radon-thoron progeny pre- filtersfor reducing the background contamination. Theflow to either LSC is switched by microprocessor

Fig. 2a: Schematic diagram for high sensitivity radonmonitor (ECAS)

Fig. 2b: Photograph of high sensitivity radon monitor(ECAS)

Fig. 3a: Schematic diagram for online thoron monitor Fig. 3b: Photograph of online thoron monitor



at the intervals specified through programmableparameters. During each interval, while one cellcounts the background, the other cell measurescounts due to both thoron and the backgroundactivity. The unit automatically calculates andlogs the thoron concentration data in the memory.

Performance evaluation

Various tests were carried out under controlledconditions in a chamber to evaluate theperformance of the monitors. The first set ofexperiments was carried out to compare themeasurements of online radon monitors againstthe commercially available systemAlphaGUARD. A fair agreement was seenbetween ECAS, SRM and AlphaGUARD asshown in Fig. 4. Similarly, the measurementswith the indigenous thoron gas monitor wascompared with that obtained with thecommercial unit RAD-7 (Fig. 5). Since thebackground is high at higher thoronconcentrations, the thoron monitor is tested upto2 MBq/m3. For both the monitors, the variationswere within 3%.

To evaluate the response time of SRM radonmonitor and also to study the effectiveness ofalgorithm based calculation, the measurementsof radon counts and concentration for sudden

rise and fall of radon was carried out which isshown in Fig. 6. The radon concentration ofthe order of 10 KBq m-3 was suddenly introducedinside a closed chamber and after 3 hrs, it wassuddenly brought down to 100 Bq m-3 (a factorof 100). The gross counts show a slow rise dueto time taken to build-up and a slow fall due tothe presence of residue activity. However, thealgorithm used for the estimation of radonconcentration as measured by SRM correctsfor these delays and depicts the sharp changesin the concentration as expected. To demonstratethe capability of ECAS to operate in highhumidity conditions measurements were carriedout by varying the humidity as shown in Fig.7.As may be seen, the effect of humidity does notarise as the electrostatic voltage is not utilizedfor collection of radon progenies

Fig. 4: Comparison of radon measurements by SRM andECAS against Alphaguard

Fig. 5: Comparison of measurements of Thoron monitorwith RAD7

Fig. 6: Response of SRM radon monitor to suddenvariations in radon concentration



To assess the long term measurement capability of

SRM and ECAS radon monitor, they were operated

continuously in a room for about two weeks with-

out any manual attendance. Both the instruments

performed successfully with agreements in radon

concentration as seen by the trends given in Fig. 8.

Fig. 7: Radon concentration measurements with varyinghumidity conditions

Fig. 8: Ambient radon measurements by ECAS and SRMfor a period of about two weeks

Table 1: Technical Specifications of online radon/thoron monitor

Parameters Online Radon Monitor Online Thoron monitor

Sensitivity ECAS: 2.8 cph/(Bq/m3) 0.7 cph/(Bq/m3)SRM: 1.2 cph/(Bq/m3)

MDL ECAS: 8 Bq/m3 at 95% confidence, 15 Bq/m3 at 95% confidence,1 hr counting 1 hr countingSRM: 14 Bq/m3 at 95%confidence,1 hr counting

Upper Detection Limit 50 MBq/m3 50 MBq/m3

Cycle time 15 / 30 / 60 min – Fast mode 10 / 30 / 60 min1 / 2 / 3 h – Sensitive mode

Radon Response time 20 min for 95% of radon in air 10 min for 95% of thoronin air

Thoron Interference < 5% using thoron discriminator Not applicable

Humidity and Trace gas <5% in ambient environment Negligibleeffect (20% to 60% RH) and <10% in

highly humid environment(60% to 95% RH) for ECAS.Negligible for SRM.

Additional tests were also carried out in controlled

conditions to obtain technical specifications of ra-

don and thoron monitors. These specifications are

summarized in Table 1.



Applications of radon monitors

The features such as uninterrupted onlineoperation, high sensitivity and free fromhumidity / trace gas interference open up diverseapplications in radon and thoron studies. Theseinclude calibration of passive detector systems,indoor/outdoor radon monitoring, networkbased online radon monitoring in workplaces suchas underground uranium mines, radon emissionstudies from soil/water/building materials, fieldsurvey and site monitoring such as uraniumtailings pond. Some of the potential applicationshave been demonstrated below.

Measurement of radon emission from soil andbuilding materials.

Soil in the earth’s crust is the major source ofradon emission into the environment. We havedemonstrated the use of ECAS for measuringthe rate of radon emission from soil. The“accumulator” technique has been used for this.The soil area of interest is covered with theaccumulator and the radon build up in itmonitored using ECAS connected in a closedloop fashion with an external pump. The buildupdata is fitted to an appropriate model to extractthe radon emission rate from soil. The experimentwas conducted in an open ground (Fig. 9). The

accumulator technique of Sahoo and Mayya(2010) was followed to measure the radonemission rate from soil which was found to be80 Bq m-2 h-1. This was close to the valueobtained using RAD-7. Knowing that buildingmaterials are the second most importance sourceof radon, we used ECAS to measure the radonemission from cement samples (Fig. 10) using

Fig. 9: Measurement of radon emission from soil

Fig. 10: Measurement of radon emission from a cementsample

Fig. 11: Schematic diagram of Radon monitoring networkat Turamdih U Mines

the mass exhalation measurement procedure ofSahoo et. al. (2007). The emission rate was foundto be 7.2 mBq kg-1 h-1 which falls within therange reported by Sahoo et al., 2007.



Networking in Uranium mines atTuramdih - field trial

The networking capability with fast response ofECAS is useful for monitoring uranium minesand tailings pond, with multiple such unitsnetworked to give real-time spatial profiles ofradon. In this context, few online monitors wereinstalled inside the uranium mines (Fig.11) at thelocations where the concentration of radon isexpected to be high. Results of themeasurements are shown in Fig.12.

indigenous monitors will serve as importsubstitutes for the Indian radon/thoron researchprogrammes.

Acknowledgements

The authors would like to thank Mr.. H.S.Kushwaha, Ex-Director, HS&EG and Dr. A.K.Ghosh, Director, HS&EG, BARC, for theirconstant encouragement and support towardsthis work.

References

1. Abbady A, Abbady AG, Michel R., Indoorradon measurement with the Lucas celltechnique, Appl Radiat Isot., 61(6)(2004):1469-1475.

2. Lucas F.H. Improved low-level alpha-scintillation counter for radon. Rev. of Sci.Inst., 28 (1957): 680-683.

3. Sahoo BK, Mayya YS. Two dimensionaldiffusion theory of trace gas buildup in soilchambers for flux measurements. Agric.and Forest Meteorol. 150 (2010):1211-1224.

4. Sahoo BK, Nathwani D, Eappen KP,Ramachandran TV, Gaware JJ, Mayya YS.Estimation of radon emanation factor inIndian building materials, Rad. Meas. 42(2007): 1422-1425.

Fig. 12: Radon levels monitored at various locationsinside Uranium mines

Summary and Conclusions

Different versions of online radon and thoronmonitors have been developed using ZnS(Ag)detector for applications in front end nuclear fuelcycle. Special features of these monitors includelow cost, high sensitivity and non- interferenceof humidity and trace gases. The performanceof these monitors were tested successfully bothin laboratory and field conditions. They find wideapplications for networked based radonmonitoring in U mines, tailings pond region andstack monitoring of thoron release in a thoriumprocessing facility. Being highly sensitive, theycan also be used for ambient measurements suchas radon/thoron monitoring in dwellings, radonexhalation measurements, thoron emissionmeasurements from monazite sands etc. These

B A R C N E W S L E T T E RFEATURE ARTICLE


Formal Model Based Methodology forDeveloping Software for Nuclear Applications

A. Wakankar, R. Mitra , A.K. Bhattacharjee, S.V. Shrikhande,

S.D. Dhodapkar, B.B. Biswas and R.K. Patil

Reactor Control Division

Abstract

The approach used in model based design is to build the model of the system in graphical/textual language. In

older model based design approach, the correctness of the model is usually established by simulation. Simula-

tion which is analogous to testing, cannot guarantee that the design meets the system requirements under allpossible scenarios. This is however possible if the modeling language is based on formal semantics so that the

developed model can be subjected to formal verification of properties based on specification. The verified

model can then be translated into an implementation through reliable/verified code generator thereby reducingthe necessity of low level testing. Such a methodology is admissible as per guidelines of IEC60880 standard

applicable to software used in computer based systems performing category A functions in nuclear power plant

and would also be acceptable for category B functions.

In this artical, we present our experience in implementation and formal verification of important controllers

used in the process control system of a nuclear reactor. We have used the SCADE (Safety Critical SystemAnalysis & Design Environment) environment to model the controllers. The modeling language used in

SCADE is based on the synchronous dataflow model of computation. A set of safety properties has been

verified using formal verification technique.

Introduction

The approach used in model based design is tobuild the model of application in some modelinglanguage and then obtain the implementation ina programming language automatically usingcode generator. In older model based approach(e.g. UML tools [1]), the correctness of themodel is mainly established by simulation.However simulation cannot guarantee that thedesign meets the system requirements under allpossible scenarios. This is possible only if themodeling language is based on formal semanticsand the model can be subjected to formalverification of system properties, which arederived from system requirements. Verification

of these properties establishes that the modelmeets the system requirements. Such a modeldriven design methodology where the modelinglanguage has formal semantics and environmentsupports formal verification of properties istermed here as Formal Model Based DesignApproach [2].

The advantage of this approach is that, anychange in the requirement can be directlyintroduced in the model and verified (both viasimulation and formal verification) before codeis generated automatically, thereby keeping theimplementation in sync with the design. This is asignificant advantage in implementing changerequests.



Such methodology for the development ofsoftware used in safety class applicationsconforms closely to the design guidelinesrecommended by IEC60880. In fact since it ispossible to rigorously verify safety properties,the design process can meet most of theguidelines in appendix E of IEC60880. Sinceuse of formal model based technique representedmethodology change, it was decided to carry outimplementation for two important controllers forwhich earlier implementation existed forcomparative purposes. SCADE [5], a modelbased design environment was chosen for thispurpose. SCADE supports a graphical modelinglanguage having an underlying formal semanticsdefined on synchronous dataflow model ofcomputation. The SCADE environment alsosupports model simulation, model test coverage(MTC) analyzer, formal verification tool andcertified code generator. It allows modelverification through interactive simulation andformal verification. Another important aspect isthat the SCADE models are built using graphicalnotation that is easily understood, thus greatlyhelping to simplify review of models by controlengineers.

Two controllers viz Steam Generator PressureController (SGPC) and Primary Heat TransportPressure Controller (PHTPC) were selected forimplementation. These controllers were earlierimplemented using conventional softwaredevelopment techniques and are in actual use.In that way it was possible for us to comparethe effectiveness of the new technique. Thecomplete development process was followedwhich included modeling, simulation, testcoverage measurement and code generation.This was followed by testing in target hardwarewith I/O simulation. For the verification of safetyproperties the SCADE Design Verifier wasused. Two controllers were implemented usingSCADE but only SGPC controller is describedherein.

BackgroundProcess Control Systems in Nuclear Reactor

The objective of SGPCS (Steam GeneratorPressure Control System) [8, 9] is to regulatethe steam generator (SG) pressure by controllingthe total amount of steam drawn from the SG.The heat input to the SG through Primary HeatTransport system is a function of reactor power,which is controlled independently. When theenergy in the steam drawn from SG equals theenergy released from reactor fuel into the primarycoolant, the primary fluid temperature and steamtemperature (and hence the pressure) aremaintained at steady values. The steam pressureregulation is achieved by controlling the valvesin various steam lines taking steam to either theturbine (turbine governor valves TGVs) ordumping into condenser (condenser steamdump valves CSDVs) or discharging toatmosphere (atmospheric steam dischargevalves ASDVs). So the objective of the SGPCsystem is to generate the control signals forvalves specified above. The control signal isgenerated by applying PID control algorithm tothe error signal calculated based on thedifference between measured SG pressure andoperational pressure setpoint (OPSP). Theoperational pressure setpoint is function ofreactor power and is calculated using no loadsetpoint (NLSP) and DT, the measureddifferential temperature across SG, which is ameasure of reactor power. The main controlsignal is generated by applying PID controlalgorithm to the error, which is then split intothree ranges to derive control signals for thethree types of actuating valves i.e. TGVs,CSDVs and ASDVs. Since these controllersperform critical functions, the inputmeasurements are triplicated /quadruplicated toprovide redundancy.



SCADE Specification Language

The SCADE [5, 6] modeling notation supports

Dataflow Equation and Safe State Machine for

modeling the system. A dataflow equation

describes the logical relationship between input

and output variables. Safe state machine

describes the control flow in the system in terms

of state transitions. Set of dataflow equations

are evaluated in parallel unless there is a data

dependency between them. Internally the

SCADE models are represented in SCADE

textual language. SCADE textual language is

based on the dataflow formalism, which is similar

to the Synchronous dataflow language Lustre

[4].

Synchronous languages [3] are based on

synchrony hypothesis, which assumes that the

program is able to react to an external event,

before any further event occurs. In dataflow

language a program is described as network of

operators transforming flows of data. SCADE

model is graphically represented as network of

operators. For example a basic counter that

counts up from 0 can be expressed in SCADE

textual language as

N = 0 → pre (N) + 1 ...............(1)

In above equation N is a variable that stores the

value of counter at a given instance of time. The

operator → is called the “followed by” operator

and it is used for initialization. Operator “pre” is

used to refer to the value of variable at previous

instant of time. Therefore the above equation

specifies that the initial value of variable N is 0

and thereafter its value is one more than the

previous value.

Fig. 1: SCADE Operator Diagram

SCADE model corresponding to above equation

is shown in Fig.1. A network of operators in

SCADE can be encapsulated as a new reusable

operator that is called a node or SCADE operator.

The requirements of the system to be

implemented are mapped in the form of network

of SCADE operators, where each operator

provides a specific functionality independently

or by interaction with the other SCADE

operators.

SCADE Suite contains an editor for modeling

the system behavior, a SCADE model simulator

for validating the model with the help of test cases,

a SCADE MTC module for accessing the

coverage of the model during simulation (based

on MC/DC structural coverage criteria) and a

SCADE Design Verifier to apply formal

verification technique for proving important

properties of developed SCADE model.

SCADE Design Verifier supports formal

verification based on model checking technique.

The verification engine supports two kinds of

verification; debug mode, which involves

bounded model checking [10] and proof mode

involving exhaustive verification. A property that

is shown to be true in debug mode (bounded by



given depth) should not be assumed to be

true under all possible cycles of execution.

The proof strategy can take enormous

amount of time (may not terminate in a

bounded time) if the property is not verifiable

within certain search depth because thesystem may have very large state space.The verification interface provides strategyoptions for terminating the search if theverification is not successful within a specifiedamount of time. It is to be noted that the propertyverifications reported in the later part of the paperwere done using the proof mode.

Development of the Model for SGPCS inSCADE

The processing logic of the SGPCS can becategorized as Signal Processing Logic andControl Logic

This is shown schematically in Fig. 2. Forall the important processes parameters,triplicate or quadruplicate measurements areprovided. Signal processing logic performsthe validation of input signals and generationof “representative” (good) signal for eachinput parameter from multiple measurementsrejecting where necessary any faultymeasurements, to ensure reliable operationeven in case of some sensor failures.Control logic involves the implementation ofprocess control algorithm for SGPC system.The “representative” signals from signalprocessing logic are the inputs to the control logicand it generates the required control signal forTurbine Governor Valves (TGVs), CondenserSteam Dump Valves (CSDVs) and AtmosphericSteam Discharge Valves (ASDVs). The formalmodel has been developed in SCADE only forthe Application Control Logic since thiscomponent could be cleanly substituted in oldimplementation without any other modification.

The equations expressing relationship betweenoutput and input variables were grouped andimplemented graphically in SCADE as differentnodes, according to the functionality theyprovide. In this way the SCADE model ismodularized and these modules can be reusedin other implementation. The representativesignals for all the discrete and analog inputs thatare used in the model are read from the interfaceof the signal processing logic alreadyimplemented in the existing code.

Fig. 2: SGPCS Inputs and Outputs

Fig. 3: SCADE Nodes and Data Flow

Control Logic is divided into nodes. The nodes,which generate actual control signals areCalc_NLSP, Calc_Control_Signal andCalc_ASDV_Control_ Signal. The function ofthese nodes is to generate “No Load Set Point(NLSP)”, “Control Signal for TGVs andCSDVs” and “Control signal for ASDVs”respectively as shown in Fig. 3.



model is simulated, we have used Model TestCoverage (MTC). MTC is a SCADE Suitemodule, which allows measuring the coverageof model during model simulation activity.SCADE MTC analyzer uses MC/DC [7]structural coverage criteria to assess the modelcoverage. The MTC is done by using the scenariofiles stored during the model simulation. The useof scenario files ensures that the same test casesare applied during simulation and MTC. Hencethe coverage results observed after MTC showsthat how extensively the behavior of the modelwas simulated and points out the part of themodel that was not covered during modelsimulation. We can then design new test casesfor covering those parts of the model that arenot covered. By applying test cases as per thepreviously prepared test plan, we could achieve97 percent model coverage.

From the analysis of the operators that were nottested using the test plan, we designed new testcases for increasing the model coverage. Anexample for derivation of such a test case canbe illustrated using the Fig.6. Each operatorin the figure is labeled with an instance numberto distinguish between two instances of same

Fig. 4: Schematic of SCADE Node Calc Control Signal

Fig. 5: Hierarchical architecture of SCADE model ofSGPCS

The lower level nodes realize the controlfunctionalities like PID control withinCalc_Control_Signal, lookup tables and rangeconversion algorithms. Fig. 5 shows thehierarchical architecture of the SCADE modelof SGPCS, along with the coupling among nodesand number of instances of each node.

Validation of SGPCS model

The validation of SGPCS model is done bysimulating the SCADE model. We have to applya sequence of input vectors to test a given systembehavior. The trend of outputs with the appliedinput sequence is observed and compared withthe expected outputs, for analyzing thecorrectness of the model. Each test sequencethat may expand over several cycles is storedas a separate scenario file. The scenario filestores the value of all the input vectors appliedduring each cycle. The scenario files are usefulto automatically regenerate the previouslyconducted test whenever required.

To assess how thoroughly the behavior of the

Calc_Control_Signal is the most complicatednode because this node implements the algorithmfor computation of pressure set point (OPSP)for SG and calculates the control signal byapplying PID control algorithm to the error signal.The brief overview of node Calc_Control_Signalis depicted in Fig. 4.



operator. So to identify each operator uniquelyduring illustration, we have used operator namefollowed by its instance number e.g. the ANDoperator labeled with instance number 2 will bedepicted as AND2. Similarly the inputs of eachoperator are identified as I1, I2…In, depicting1st, 2nd … nth input respectively. In the figurebelow MTC shows that the operator AND2 isnot covered completely. According to the MC/DC criteria the three input AND gate, havinginputs I1, I2 and I3 is said to be coveredcompletely if the following conditions aresimulated.

� I1, I2 and I3 are true� Only I1 is false� Only I2 is false� Only I3 is false

The coverage analysis shows that, for theoperator AND2 the condition “Only I2 is false”was not simulated. From the Fig.6 it could bedetermined that to simulate this condition, weshould have an input combination whereNOT(ASDV_auto) is true, NOT(ASDV_HC)

is false and ASDV_CM_raise is true. Thisderived input test vector is added to the test planto increase the model coverage.

We have also observed that some conditionsrequired to completely cover the operatoraccording to MC/DC criteria were physicallyinfeasible. Fig.7 shows one such condition. TheMTC in this figure shows that the operator AND6is not covered because the condition “only I1 isfalse” was not simulated. To simulate thiscondition, input I1 for operator AND6 should befalse keeping inputs I2 and I3 as true. I2 for theAND6 is output of operator timer1. The outputof timer1 operator becomes true only if input istrue for specified time interval or more; otherwiseits output is false. So it can be determined that ifI1 is false then output of timer1 will be false andhence I2 will also be false i.e. whenever I1 isfalse, I2 will also be false. So we cannot designtest case, which simulates the condition “only I1false” for the operator AND6.

Fig. 6: Derivation ofTest Case from theResult of MTC

Fig. 7: Part ofCalc_Control_Signalnode



Infeasible scenarios as described above had tobe left out and hence it was possible to achieve99.8 percent model coverage.

Formal Verification of Requirements ofSGPCS

The verification of the SGPCS model was carriedout by using the formal verification techniquecalled model checking. It involves expressing asystem requirement as a property and checkingwhether property is satisfied by the model. Eachof the properties to be verified was modeled asan “observer node” using built-in SCADEverification operators. The composition of“observer node” with the system model wasused for model checking using the SCADEDesign Verifier.

Some of the important system properties ofSGPCS that were formalized and verified areexplained below. Each property is first stated inEnglish as it appears in specification followedby brief explanation. Later the property is statedformally using SCADE notation and explanationis provided whenever required.

Property1

If manual_crash_cool or auto_crash_coolsignal is true then No Load Set Point (NLSP)should decrease till lower saturation limit(100.0) is reached.

The signals manual_crash_cool andauto_crash_cool are two discrete inputs, whichare used to maneuver the pressure setpoint(NLSP) during some emergency condition. Ifat least one of these inputs is true then NLSP isdecreased till the limiter clamps the value ofNLSP to 100.0

Formal Specification of the property1 in SCADEis shown in Fig. 8. In figure, the block“verif::implies” implements the mathematicalimplication (p!q). The first input denotes ‘p’ andsecond input denotes ‘q’. The output of the blockis true if (p!q) holds. The output of this block isassigned to the Boolean output property1.

Property 2

If NLSP_lower and NLSP_raise both signalsare true then NLSP should decrease till lowerlimit (100.0) is reached.

The signals NLSP_lower and NLSP_raise arediscrete inputs used to lower and raise the valueof NLSP respectively, however if both thesignals are true simultaneously thenNLSP_lower signal must have a higher priorityover NLSP_raise.

Formal Specification of the property2 is shownin Fig. 9.

Fig. 8: SCADE Observerfor Property1

Fig. 9: SCADE Observerfor Property2



Property3

If the loss_of_electric_load or turbine_tripsignal is true and reactor power exceeds 20%Full Power then Anticipatory Action (AA)should start and should get completed in timeT1+T2, where T1 and T2 are predefinedconstants. AA lowers the operational set point(OPSP) in proportion to reactor power basedon the following equation.

OPSP = NLSP - K *DT .......................(2)

The variation of K before, during and after AAis shown in Fig.10, where K1 and K2 are positiveconstants.

In SCADE, the time is measured in terms ofnumber of execution cycles. The number ofexecution cycles in time T1+T2 can bedetermined by dividing time T1+T2 by samplingtime (0.175 sec). The value of T1 and T2 is 1and 2 respectively. Hence the number ofexecution cycles is (1+2)/0.175 = 17.14 = 17.However Fig.10 shows that the value of K atthe first and last cycles is equal to K1. Thereforethe number of cycles during which AA will bepresent is two less than the calculated numberof cycles in time (T1+T2). Hence AA shouldappear for (17-2) =15 cycles”.

Formal Specification of the property3 in SCADEis shown in Fig.11. In figure the block specifies an if-else condition as “O1= if C1 thenI1 else I2”. The block verif::AfterNthTick isused to express that the output equals input,except for the first N (N=1) cycles during whichthe output is true. The blockverify::AtLeastNTicks express that the outputequals the input as soon as the input is true forN=15 cycles, before that the output is false.Similarly the block verify::HasNeverBeenTrueis used to express that the output becomes falseas soon as its input becomes true for the firsttime, after this cycle the output remains false.

Property 4

Anticipatory action is discontinued after a reactor

trip or when both initiating conditions i.e.

Fig.10: Timing diagram for Anticipatory Action

Fig.11: SCADEObserver forProperty3

The signals loss_of_electrical_load andturbine_trip are the discrete inputs to theSGPC model, which decide the condition for startand termination of AA



loss_of_electrical_load and turbine_trip arenot true.

This property specifies the condition for thetermination of anticipatory action. Thus ifrequired condition for anticipatory action doesnot exist or if it disappears then anticipatoryaction will terminate.

The formal specification of the property4 inSCADE is shown in Fig.12.

Property5

If ASDV is in computer manual mode (i.e.ASDV is neither in auto mode nor in handcontroller mode) and

a) ASDV_CM_raise is true andASDV_CM_lower is false thenASDV_control_signal will increase.

b) ASDV_CM_raise and ASDV_CM_lowerboth are true then ASDV_control_signalwill remain unchanged.

c) ASDV_CM_raise is false andASDV_CM_lower is true thenASDV_control_signal will decrease.

The final control signal for ASDVs is calculatedbased on the mode of operation. ASDVs can bein one of the three modes: auto, hand controlor computer manual, which are selected froma three-position switch. Hence in the model the

mode is determined by two input variablesASDV_auto and ASDV_HC. If inputASDV_auto is true then mode is auto, if inputASDV_HC is true then mode is hand controllerand if both inputs are false then mode is computermanual. Inputs ASDV_CM_raise andASDV_CM_lower are used to raise and lowerthe ASDV_control_signal respectively.

The formal specification of the property5 inSCADE is shown in Fig. 13. The property couldnot be proved and a counter example wasgenerated. The property could not be provedbecause the specification does not place anyrestriction on mode of ASDV in the instantbefore coming to computer manual mode.Therefore if in the previous instant the modewas other than computer manual the controlsignal values before and after mode change donot conform to the property specification. Themodel was later corrected to implement thebumpless transfer functionality.

The time required for verification of theseproperties was found to be less than 10 secondson a XEON Server with 4GB RAM.

Code Generation and Integration

SCADE environment provides IEC61508 SIL3certified automatic code generator (KCG). Theverified model was used to generate the C codeautomatically. The use of certified code

Fig.12: SCADE Observer for Property4



generator ensures that every specification in themodel is correctly reflected in the code, whicheliminates the need for unit testing.

The SGPC module developed using SCADEwas integrated with prototype system in the lab.This was done by replacing old handwrittenSGPC code by the one developed with SCADE.

Two identical hardware based controller setupswere available. One was loaded with the oldhandwritten SGPC code. This implementationis in use for several years. The other controllerwas loaded with automatically generated codefrom the SCADE model. There was nodiscrepancy observed in the output of these twosystems during testing.

The final size of the executable generated was~163 KB whereas the size of old executablewas ~167 KB, which was comparable.

Fig.13: SCADE Observers for Property5a, Property5b and Property5c

Conclusion and Future work

This methodology is suitable for the systemswhose output behavior involves cyclic executionsof read, compute and output. Software basedcontrollers used in embedded control applicationstypically fall in this class of systems. It has beenour experience that it is quite easy to adopt themethodology in the design life cycle of suchsoftware and comply with the recommendedpractices of IEC60880. This is because theSCADE environment supports a formal languageand has tool support for testing the modelconforming to MC/DC structural coverage andformal verification. The availability of IEC 61508SIL3 certified code generator has reduced thecode generation effort to a push button andthere is no effort required for low level testing.It must be emphasized that once the model isvalidated and code is generated from the model,it is not recommended to do any manual changes



in the generated code. The availability ofcertified code generator is a great advantageover the other traditional developmentmethodologies (e.g. UML) involving modelinglanguage having less formal semantic foundation.The lack of semantics in such modeling languagehinders complete automated code generation andhence no certifiable code generation is possiblefor the entire modeling language.

During formal verification, it was observed thatmost of the time was spent on reviewing propertyexpressed in SCADE with corresponding Englishspecification. Although the tool supports an easyto use interface to the back end verificationengine, the user is expected to know thelimitations of formal verification of systemsinvolving integer, real and nonlinear arithmetic.

SCADE supports predefined operators forspecifying verification conditions. Howeverformal logics such as LTL are more expressiveand it is possible to express properties much moresuccinctly in these notations. For example, theproperty 3, in section V.C, could have beenspecified as (s → (p U15

q)), where s is theinitiating event (turbine trip or loss of electricalpower), p is the Boolean condition foranticipatory action and q is the Boolean conditionsignifying the end of anticipatory action. The sub-expression p U15 q in the verification conditiondemands that p is true for 15 ticks andhenceforth q is true and the complete propertystates that if s is true and remains true then pshall remain true for 15 ticks and subsequently qshall remain true. It is felt that such propertiesare difficult to express using standard SCADEblocks. SCADE does not support a tool that cantranslate specifications in such logic as explainedabove into equivalent SCADE propertyobservers. We are now working on to developsuch a property synthesis tool and integrate inthe SCADE environment.

Acknowledgements

We are thankful to Shri G.P. Srivastava, DirectorE&I Group for his encouragement during thiswork. We are thankful to Shri C.K. Pithwa,Head, ED (earlier Head, CCDS, RCnD), forproviding us the initial specification of SGPCSfrom which the formal model has beendeveloped. Thanks are also due to Mrs. RatnaBhamra for helping us to understand the initialspecifications.

References

1. Unified Modeling Language http://www.omg.org/technology/ documents/formal/ uml.htm.

2. A. Wakankar et. al., Formal Model BasedMethodology for Developing controllers forNuclear Applications, Proceedings of 20thIEEE International Symposium on SoftwareReliability Engineering (ISSRE-2009),Mysore, India.

3. N. Halbwachs, Synchronous programmingof reactive systems. Kluwer Academic Pub,1993.

4. N. Halbwachs, P. Caspi, P. Raymond andD. Pilaud, The synchronous dataflowprogramming language Lustre. Proceedingsof the IEEE, vol. 79(9). September 1991.

5. SCADE Tool http://www.esterel-technologies. com/.

6. SCADE Language Reference Manual, Ver6.1, Esterel Technologies Ltd., France

7. SCADE User Manual, Ver 6.1, EsterelTechnologies Ltd., France

8. S. Glasstone and A. Sesonske NuclearReactor Engineering, Chapman & Hall,New York.

9. Software Requirement Specification forDPHS-PCS Rev 2 USI 63000 InternalDocument RCnD, BARC, Feb. 2005

10. A. Biere, et.al., Bounded Model CheckingVol. 58, Advances in Computers, 2003(Academic Press).



Development of Digital RadiotherapySimulator: A Device forTumour Localization,

Radiotherapy Planning and Verification

D.C. Kar, R. Sahu, K. Jayarajan, D.D. Ray and Manjit Singh

Division of Remote Handling and Robotics

Abstract

Radiation therapy is one of the established modes of cancer treatment. For the safe and effective radiationtherapy, it is necessary to plan and deliver the radiation beam accurately. Radiotherapy Simulator helps in

identifying the organs at risk and in localising the cancer-affected tissues. For teletherapy, the Simulator would

also help in choosing the right radiation beam and aiming it at the target. Although, radiotherapy simulator is anessential tool for improving the quality of teletherapy, there is acute shortage of such machines in our country

due to the high cost of the imported units and the lack of indigenous technology. In fact, many cancer hospitals

with teletherapy units do not have radiotherapy simulator. Considering the growing incidence of cancer andthe need for such devices, Bhabha Atomic Research Centre (BARC), Mumbai has recently developed

a Radiotherapy Simulator. This article briefly describes some of the features of the indigenous Radiotherapy

Simulator.

Introduction

Cancer is a major health concern in our country,and majority of the patients require radiotherapyduring the course of treatment. Radiotherapysimulator is a machine that helps in radiotherapyplanning, prior to the treatment delivery. It helpsto diagnose the physical extent of the tumourand its relation to the surrounding tissues forproper selection of the size and orientation ofthe radiotherapy beams. It also helps to plan thetreatment, to protect the critical organs adjacentto the tumour to be treated. The capability of asimulator for real-time review of the images andtheir analysis helps in accurate planning andverification in a short time. Advances inacquisition, storage and transfer of images havedramatically improved the image quality leading

to improved performances in radiation therapyplanning [1].

In India, there is wide gap between the demandand availability of radiotherapy facilities [2].Among the few centres with teletherapy facilities,many do not have radiotherapy simulator foraccurate delivery of radiation therapy. Theygenerally depend on conventional radiographyunits for tumour localization.

In the conventional form, a radiotherapysimulator is similar to an isocentric external beamtherapy machine. It can reproduce the geometricmovements of (external beam) radiotherapymachines. However, unlike a teletherapymachine that delivers high-energy radiationbeams for treatment, a radiotherapy simulator



uses diagnostic X-ray beams for imaging,either in radiography or fluoroscopy mode.Unlike the complex CT-Simulators, whichperforms virtual simulations, radiotherapysimulators are less expensive, and easy tooperate and maintain [3]. The conventionaldesign of Radiotherapy Simulator does not poseany restriction on the size of the patient.

Considering the growing requirement for suchmachines in our country, BARC has initiated thedevelopment of radiotherapy simulator. Thedevelopment is successful and the first indigenous

collimator subassembly and the X-ray tube. Theimaging subsystem is mounted on the other endof the C-arm. The collimator sub-assembly canmove radially closer to or away from theisocenter to change the focus to axis distance(FAD). This helps the simulator to adapt withteletherapy machines of different source to axisdistances.The image intensifier arm also canmove radially closer to or away from theisocenter. This helps in capturing images withvarying magnifications and avoiding collisionbetween the image intensifier and the couch,during continuous gantry rotation.

Fig. 1: Indigenous Radiotherapy Simulator installed atIndian Red Cross Society Hospital, Nellore, AP

Fig. 2: Schematic layout of the Radiotherapy Simulator

unit is installed in Indian Red Cross SocietyHospital, Nellore, Andhra Pradesh (Fig. 1). Thisarticle describes the development in brief.

Brief Description of the Unit

Major sub-systems in the radiotherapy simulatorare gantry, collimator, X-ray tube, imaging unit,patient support/positioning system, and remotecontrol console. The schematic layout of themachine is shown in Fig. 2.

GantryThe Gantry consists of a C-arm, which can rotateabout the longitudinal axis passing through theisocenter. One end of the C-arm holds the

CollimatorThe aperture control mechanism or the collimatorprovides a rectangular opening of the X-raybeam. Each side is independently controlled togenerate an arbitrary rectangular radiation field.Both pairs of the jaws can be moved insymmetric as well as asymmetric mode. Thecollimator is designed with over-travel to suit thelatest radiation therapy units. Four independentlyactuated delineator wires are provided to definethe tumour boundary within the radiation field(Fig. 3). The collimator assembly can also berotated about an axis orthogonal to the gantryrotation axis, passing through the centre of theX-ray beam.



To visualize the projection of the X-ray field onthe patient’s skin, a field light projectionmechanism is used. An optical distance indicator(ODI) system is also mounted on the collimatorto facilitate measurement of focus to skindistance by projecting an optical scale onpatient’s body.

X-ray TubeThe X-ray Tube is of rotating anode type withdual focal spots (0.4mm, 0.8mm) for sharperimage. It has high heat storage capacity for

CouchThe patient support/positioning system or couchis a pit-mounted, isocentric platform with fourindependently actuated motions: vertical linear,lateral linear, longitudinal linear, and isocentricrotation. It has a radio-transparent thin sheet ofcarbon-fibre composite mounted on the top. Thecouch platform can be lowered to a levelconvenient for the patient to lie down. Twokeypads (Fig. 4) are mounted on either side ofthe couch at convenient locations for interactivepatient setup. All the motions of the gantry,collimator, and the image intensifier support armcan be controlled through these keypads as wellas from the remote control console. The valuesof important positioning parameters aredisplayed on the wall-mounted display monitor.The patient remains immobilized duringsimulation with the help of restraining straps,

Fig. 3: Schematic layout of the collimated field

Fig. 4: Keypad located on the sides of the couch

uninterrupted usage. 15° anode angle is adequateto cover X-ray field sizes required forradiotherapy simulation applications.

Imaging Sub-systemThe imaging subsystem consists of a12" tri-fieldimage intensifier coupled with 1024 x 1024 - pixelCCD camera system. It provides sharp digitalimages in fluoroscopy as well as radiographymode. It is interfaced with microprocessor-controlled HF generator for quick imageprocessing. Automatic exposure control ensuresuniformity in dose per image. The camera-lensassembly captures the images and passes indigital form. The image intensifier support armhas two orthogonal (lateral and longitudinal)motorized motions for remote and interactivepositioning of the image intensifier at the regionof interest.

blocks, masks etc to minimize patient’s motionduring simulation. This couch also has theprovision for the use of indexed positioningdevices for fast and accurate reproduction of asetup.

Control ConsoleThe control console is located at a remotelocation outside the simulator room. Afterimmobilizing the patient on the simulator couch,the operator leaves the room, and operates themachine from this console. The control consoleconsists of a desktop computer, a mouse,



a physical key switch, and two buttons foractivating the X-ray beam. One more desktopcomputer is used for display and storage of theacquired images. The operator can control allthe unit motions, viz. gantry, collimator, imagingarm and the couch, through the graphical userinterface as shown in Fig. 5. The digital readoutsfor all the motions remain displayed on theconsole. For imaging, the operator can selectone of the two modes : fluoroscopy orradiography. In fluoroscopy mode, the liveimages of any moving organ can be viewed. Thismode can also be used while one or more unitmotions are active, for determining appropriatebeam (for therapy) directions. Static anatomicalimages can be captured in the radiography mode.For either of these modes, the operator can selectthe exposure parameters, such as kV, mA andmAs.

Important features viz. automatic correction ofimage distortion, last image hold, MLC (multileaf collimator) overlay, DICOM (digital imagecommunications in medicine) compatibility,storage and management of acquired images,annotations, image manipulation and viewingtools, printing etc. are implemented for theconvenience of the user as well as smoothworkflow.

Auxiliary sub-systemsPatient Positioning LasersAccurate patient positioning is essential foreffective treatment simulation. The laser systemconsists of three linear red diode lasers: two incross planes and one in sagittal plane. It is similarto the laser system used for teletherapymachines. The projections of these lasers markthe isocentre, which serves as the reference for

Fig. 5: Graphical user interface at the control console



various setup parameters in order to reproduceexact positions on treatment machines.

Safety Interlocks and Emergency StopButtons

Many safety interlocks are provided to protectthe patient and the operators from unwantedexposure to radiation. These include doorinterlock of the treatment room (to preventexposure by accidental opening of door), externalmains power supply interlock and emergencyinterlock (due to fault in any of the unit motions).Emergency stop buttons are installed in the basehousing, couch, door, control console and on thepassage wall inside the room.

Visual Monitoring

Radiotherapy simulation requires special roomswith adequate shielding to protect the operatingpersonals, the public as well as the environmentfrom the harmful effects of ionizing radiation.During simulation, the patient is monitoredcontinuously from the control console throughthe lead-glass window.

Wall Mounted Display

A monitor in the treatment room displaysimportant parameters related to the machine.Whenever an authorized user logs into thesystem, system parameters like FAD, imageintensifier distance, gantry rotation angle,collimator rotation angle, positions of thecollimator blades, delineator wires, couchlongitudinal, lateral, vertical and isocentricrotation etc. are displayed in the monitor.

Technical Specifications

Gantry Rotation

At FAD =100cm (°) ± 185

Isocenter height (cm) 128

Max. Speed (rpm) 1

Auto stops (at deg) ± 90 & ± 180

Anti-collision Logic

Focus to Axis Distance (FAD)

Range (cm) 80-120

Auto stop at FAD(cm) 80,100,120

Max. Speed (cm/min) 100

Collimator

Rotation (deg) ± 95

Max. Speed (rpm) 1.0

X-ray field (delineators)

Field size (cm x cm) 45 x 45 (max.)

Jaw motions Independent

Max. overtravel (cm) 20

X-ray field (shielding jaws)

Field size (cm x cm) 0.5 x 0.5 to 50 x 50

Independent jaw motion Yes

Over travel (cm) 20

Pairing delineators Yes

FAD tracking Yes

Image Intensifier Arm

Support Arm Motions

Longitudinal (cm) ±20

Lateral (cm) ±20

Radial (cm) 0 to 60

Auto recenter Yes

Max. speed (cm/sec) 2.5


X-Ray Generator

Power (KW) 65

KV Peak (KVp)

Fluroscopy 40-125

Radiography 40-150

Milli Amperage (mA)



Quality Assurances and RegulatoryCompliances

Radiotherapy simulator has major influence onthe overall performance of the radiation therapyprocess. Although not used directly for the dosedelivery, its role is important in determining thetarget location, treatment planning and spatialaccuracy in dose delivery. As the simulator hasmany features of therapy machine and diagnosticradiology unit, it has to conform to requirementsof both the applications.

The unit is tested and is found to be conformingto the International Electrotechnical Commission(IEC) Standards [4-6]. The machine will be usedclinically, after the clearance by Atomic EnergyRegulatory Board (AERB).

Conclusion

The technology for our indigenous radiotherapysimulator is developed successfully. The firstmachine is installed in Indian Red Cross SocietyHospital, Nellore, Andhra Pradesh. Thiscomputer-controlled machine is simple and user-friendly. Other features of the machine, such asfilmless operations and ease of transfer andstorage of digital images can streamline theworkflow and improve overall performances ofthe department. The indigenous machine is lessexpensive, compared to imported simulators.Therefore, smaller radiotherapy centres,especially those at remote places, will be able toafford this simulator, leading to safer and moreeffective radiation dose delivery.

References

1. Cho, P. S., Lindsley, K. L., Douglas, J. G.,Stelzer, K. J., and Griffin, T. W. (1998),Digital Radiotherapy Simulator,

Image Intensifier

Tri-Field (max dia., mm) 290

Contrast Ratio 13:1

Conversion Factor 240 ((cd/m2)/(mR/s))

Central Resolution(lp/cm) 44

Couch

Motions

Vertical(cm, from floor) 68-135

Vertical speed (cm/min) 60, 110

Longitudinal (cm) 90

Longitudinal speed(cm/min) 35, 200

Lateral (cm) ±20

Lateral speed (cm/min) 35, 200

Isocentric Rotation (deg) ±95


Auto Setup Yes

Table top

Carbon fibre Yes

Transmission (mm,eq.Al) 1.0

Deflection (mm, at 90 Kg) < 2.0

Load capacity (Kg) 135

Software

PC operating System WinXP/2000

Storage of digital images Yes

Network Mode DICOM

Calibration facility Yes

MLC overlay on image Yes

Image processing tools Yes

Fluroscopy 1-20

Radiography 1-800

Power Supply 400VAC, 3phase

X-Ray Tube

Focal Spot Size (mm) 0.4, 0.8

Target Angle (deg) 15

Heat Storage Capacity (KJ) 280



Computerized Medical Imaging andGraphics, Volume 22, pp.1-7.

2. Jayarajan K., Kar D.C., Sahu R and SinghManjit, Bhabhatron: An IndigenousTelecobalt Machine for Cancer Treatment,BARC Newsletter, Founder’s Day SpecialIssue, Issue No 297, October 2008, page27-34.

3. Suhag V., Kaushal, V., Yadav, R., and Das,B. P. (2006), Comparison of Simulator- CTversus simulator fluoroscopy versus surfacemarking based radiation treatment planning:A prospective study by three-dimensionalevaluation, Radiotherapy and Oncology,Volume 78, pp.84-90.

4. IEC 60601-1 – Medical ElectricalEquipment- Part 1: General Requirementsfor Basic Safety and EssentialPerformance, Edition 3, 2004,International ElectrotechnicalCommiss ion, Geneva

5. IEC 60601-2-29 - Medical ElectricalEquipment- Part 2: ParticularRequirements for the Safety ofRadiotherapy Simulators, Edition 2,1999, International ElectrotechnicalCommission, Geneva

6. IEC 61168- Radiotherapy Simulators-Functional Performance Characteristics,Edition 1, 1993, InternationalElectrotechnical Commission, Geneva.

B A R C N E W S L E T T E RNEWS & EVENTS


National Conference on Advances in NuclearTechnology (ADNUTECH 2010): a report

A two-day national conference on Advances inNuclear Technology (ADNUTECH 2010),organized jointly by the Department of AtomicEnergy (DAE) and the Indian National Academyof Engineering (INAE) was held duringDecember 2-3, 2010 at the Nabhikiya UrjaBhavan, Anushakti Nagar, Trombay. TheConference was aimed at highlighting the recentadvances in the field of nuclear technology inIndia, including nuclear power scenario, emergingreactor technologies, nuclear instrumentation,control & computing, nuclear fuels and materials,laser, plasma and accelerator technologies,applications of radioisotopes in agriculture andhealthcare. The Conference hosted eminentexperts and academicians from the field of

nuclear technology in the country, who had beeninvited to deliver talks during various plenarysessions. Ms/s NPCIL and WIL were thecorporate sponsors of the Conference. TheConference was attended by about 400 scientists,engineers, academicians and technocrats.

Welcoming the galaxy of scientists andtechnocrats, Shri V. K. Mehra, Director, ReactorProjects Group & Convener, ADNUTECH-2010, stressed on the significance of synergybetween R & D efforts at various centres ofthe DAE and the industry, especially in the wakeof a global nuclear renaissance.

Dr. P. S. Goel, President INAE, also addressed

Dr. S.K. Jain, CMD, MDCIL inaugurating the technical exhibition at ADNUTECH. Dr. R.K. Sinha, Director, BARC(extreme left) can be seen along with other senior scientists.



the gathering. He said that the INAE aims atpromoting developments in engineering andsciences for their application to problems ofnational importance. He added that developmentsin the field of nuclear technology have proven tobe of immense benefit to the society and theAcademy would continue to support efforts inthis direction.

Dr. R.K. Sinha, Director, BARC, in his inauguraladdress, spoke about various R & D initiativestaken up by BARC. Dr. Sinha reiterated thatscientists and engineers at BARC striverelentlessly to achieve the vision of Dr. Bhabha.He stressed on the need to develop cutting edgetechnologies so that we remain in the forefront.He also highlighted the need to developtechnologies which address the needs of thesociety. He impressed upon the need to developsafe nuclear reactors in which security concernshave to be addressed in the design stage itself.The keynote address was delivered by the ChiefGuest Dr. Kirit Parikh, Chairman, IntegratedResearch and Action for Development & formerMember, Planning Commission. Dr. Parikhoutlined the ways to achieve an equitable levelof human development in India, taking into

Welcome address by Shri V. K. Mehra, Director, Reactor ProjectsGroup & Convener ADNUTECH

account, the concerns about globalclimate changes and shrinkingreserves of conventional energyresources.

Shri R. S. Yadav, AssociateDirector, Reactor Projects Groupand Secretary, OrganizingCommittee ADNUTECH-2010,proposed the vote of thanks. Hethanked all speakers, industrysponsors and DAE units forextending their whole-heartedsupport in organizing the event.

Later, a technical exhibitionshowcasing various technologies developed aspart of various programmes of DAE wasinaugurated by Dr. S. K. Jain, CMD, NuclearPower Corporation of India Limited. Variousindustries participated in the exhibition andshowcased their products.

The Conference concluded with a discussion onthe key topic “Challenges for implementingNuclear Power Programme.” The panel chairedby Shri V. K. Mehra, Director RPG & ESG,BARC also included Dr. S. K. Jain, CMDNPCIL, Dr. A. K. Suri, Director MG, BARC,Shri S. C. Chetal, Director, REG, IGCAR,Shri S. K. Chande, Vice-chairman AERB,Shri G.P. Srivastava, Director, E & I Group,Shri M. V. Kotwal, Sr. Ex VP & Director,L & T Ltd. and Shri Kaustubh Shukla, COO,Godrej Precision Engg. Ltd. Discussions werecentered around achieving installed capacity of63 GWe of nuclear power by 2030 and thecontribution of nuclear power. Panelists felt thata judicious mix of imported light water reactorsand indigenous PHWRs, would be necessary toachieve the target. Contributions to be made bydesigners, vendors, utilities, regulatory authorityto achieve the target, were also emphasized.



DAE-BRNS Workshop on“High Resolution Gamma Ray Spectrometry

(HRGS-2010)”: a report

A two-day DAE-BRNS Workshop on “HighResolution Gamma Ray Spectrometry usingHPGe detectors (HRGS-2010)” was organizedby the Radiochemistry Division, BARC,Mumbai, during October 7-8, 2010. Gamma-rayspectrometry plays an important role at everystage of nuclear fuel cycle and is usedextensively to quantify fission and activationproducts during operation of nuclear reactorsand other fuel cycle facilities, environmentalradioactivity near the site of nuclear fuel cyclefacilities and also in R&D work inRadiochemical laboratories. With the advent ofcommercially available high volume as well ashigh-resolution HPGe detectors, gamma-rayspectrometry plays an increasingly vital role indetection, identification and estimation of gammaemitting radionuclides, in the programme related

to Production and Application of radioisotopes.For quantitative estimation of radionuclides, it isnecessary to calibrate the detector for absolutedetection efficiency as a function of gamma rayenergy in a standard source-to-detectorgeometry. With an objective to bring uniformityin gamma ray spectrometric measurementscarried out at various laboratories of DAE aswell as academic institutes, an intercomparisonexercise for the measurement of gamma-rayemission rates of 133Ba and 152Eu sources usingHPGe detectors was conducted in 2002, by theRadiochemistry Division, BARC and this wasfollowed by a two-day Workshop during June19-20, 2003. It provided an opportunity for theparticipants, to assess the relative accuracyachieved by their individual laboratories andscope for further improvement.

On the dais (L-R): Dr. V.K. Manchanda, Chairman, HRGS-2010 and Head, Radiochemistry Division, BARCMr. G. Nageswara Rao, Director (O), NPCIL and Dr. S. Kailas, Director, Physics Group, BARC



It was observed that during the last seven yearsthere was significant growth in the number oflaboratories in various units of DAE, engaged ingamma spectrometric analysis of a variety ofsamples. Radiochemistry Division receives largenumber of requests form various DAElaboratories from all over the country forlectures, training and supply of calibrationstandards sources. With the main objective toget acquainted with recent progress made ingamma ray spectrometry, gamma spectrometricanalysis using advanced software, efficiencycalibration and also to bring uniformity in gammaray spectrometric measurements in various labs,the present two-day BRNS sponsored Workshopwas organized at Computer Division Auditorium,BARC, Mumbai. There was an overwhelmingresponse from various units of DAE includingBARC. A total of 127 delegates participated fromvarious units/divisions of NPCIL, ESL, HealthPhysics units, IRE, AMD, BRIT, RMC, AFFF,IGCAR and BARC.

The Workshop was inaugurated on 7th October2010. Dr. V.K. Manchanda, Chairman, HRGS-2010 and Head, Radiochemistry Division, BARCdelivered the welcome address and explainedthe relevance of this workshop. He also gave abrief account of contribution of RadiochemistryDivision for the said purpose over the years. Dr.S. Kailas, Director, Physics Group, BARC gaveinaugural address and highlighted the importanceof gamma-ray spectrometry in various activitiesin DAE and applauded the efforts of themembers of RCD for organizing HRGS-2010.Shri G. Nageswara Rao, Director (O), NPCILwas the Chief Guest and in his remarks, heemphasized the need for accurate determinationof radionuclides in nuclear power programmefor which knowledge in latest developments ingamma ray spectrometry and expertise are veryessential, for the scientists working at NPCIL.Dr. Sarbjit Singh, Convener, HRGS-2010,

Radiochemistry Division, BARC proposed thevote of thanks.

The Workshop consisted of six lectures includingdemonstration of analysis of gamma-ray spectra.The resource personnel were: Dr. A. Goswami– Interaction of gamma-ray with matter, Dr. B.S.Tomar- Detectors for gamma ray spectrometry,Dr. Sarbjit Singh – High resolution gamma –rayspectrometry, Shri S. Venkiteswaran –Instrumentation for gamm-ray spectrometry, Dr.R. Acharya – Analysis of Gamm-ray spectraand Dr. K. Sudarshan – Demonstration ofgamma-ray spectra analysis with PHASTsoftware. Each lecture was followed bydiscussion, in which sufficient time was givenfor clarifications. Lecture notes were providedto all the participants. The lecture notes containStandard Operation Procedures (SOP) for highresolution gamma ray spectrometry,determination of detector resolution, energy andefficiency calibration and relevant nuclear dataon gamma-ray standard sources.

The feedback and valedictory session was heldon 8th October 2010, in which Dr. V. Venugopal,Director RC&IG was the chief guest. Writtenas well as verbal feed back was taken from theparticipants. Dr. Venugopal gave his remarks onHRGS-2010 and appreciated the effort of RCDfor conducting this two-day workshop. Dr.Venugopal also distributed the participationcertificates to the delegates. Dr. V. K.Manchanda, Chairman, HRGS-2010, thankedDirector, RC&I Group as Chairman, RTAC,BRNS for support, all the resource persons forexcellent technical programme and delegates forvery active participation. Dr. Sarbjit Singh,Convenor, HRGS-2010 briefed about theexperience of the workshop and future work inthis regard.



Workshop on Protection against Sabotageand Vital Area Identification: a report

IAEA-India National Workshop on “Protectionagainst Sabotage and Vital AreaIdentification” (VAI) was organized atMumbai during October 4 – 8, 2010. This wasthe first National workshop organized in Indiawith IAEA on “Protection against Sabotageand Vital Area Identification”. The workshopwas held at CTCRS building, AERB complex,Anushaktinagar, Mumbai.

The workshop was inaugurated by Shri S KChande, Vice Chairman, Atomic EnergyRegulatory Board (AERB), India. The workshopwas attended by 33 participants from differentDAE organizations. Participants were carefullychosen to represent various types of nuclearfacilities like nuclear power plant, back endand front end fuel cycle facilities andregulatory bodies etc. A total of 16 facultymembers were involved for deliberationslectures and for conducting workgroupexercises. There were 4 expert faculty members

from abroad: 2 from Sandia National Laboratory(SNL), USA, one from Lithuania and one IAEAstaff member. 12 faculty members from Indiawere involved in lecture presentation and asworkgroup instructors.

The workshop duration was 5 days whichincluded 19 lectures and 7 workgroup exercises.Topics covered in the workshop were Vital AreaIdentification process, Protection againstsabotage, Policy Consideration for VAI,VAIprocess including logic development,Management and organization of VAI process.Workshop material was printed in three differentsets providing lecture presentation, text andsubgroup exercises. A Workshop CD containingall the presentations was also prepared.Workshop kit containing three printed books, aCD and other necessary materials weredistributed to all participants and faculties.

The workshop was concluded on 8th Octoberafternoon after afeedback sessionfrom the participants.Certificates weredistributed to allparticipants by Shri G.P. Srivastava, CourseDirector, Shri JoseRodriguez, IAEA,Shri Bruce Vernado,Mr. Bruce Berryfrom SNL, USAa n d D r. G e o r g i jK r i v o s h e i n f r o mLithuania.

Group of participants at the Workshop



The Health, Safety and Environment Groupconcluded of its regular one-year training coursefor science graduates. These graduates wererecruited for operational radiation protection andassociated functions of the nuclear fuel cyclefacilities. The valedictory function of this coursewas held at the auditorium of Radiation ProtectionTraining & Information Centre on November 08,2010. Dr. S. Kailas, Director, Physics Groupwas the chief guest for the function. Dr. A. K.Ghosh, Director, Health, Safety & EnvironmentGroup, Dr. D. N. Sharma, Associate Director,HS&EG, Mr. R. Bhattacharya, Secretary, AERB,Dr. P. K. Sarkar, Head, Health Physics Divisionand Mr. R. G. Purohit, Head, ORPRS, HPD werealso present on the dais. The invitees includedcourse coordinators, faculty members and seniorofficers of Health, Safety & EnvironmentGroup.

Dr. P. K. Sarkar welcomed the chief guest,dignitaries, invitees and the faculty. He presenteda brief outline of the training course which wasstarted in 1989 with the specific objective ofdeveloping trained manpower in the specializeddiscipline of radiological safety required for thenuclear fuel cycle facilities, including nuclearpower plants. He observed that, Health Physicsbeing a specialized discipline, a combination ofdifferent branches of science and engineering,is not offered as a regular course by any of theuniversities in India.

He remarked that over the years, the HealthPhysics training programme has undergonesignificant changes with respect to the syllabus,structure of the training programme, trainingmethodology, assessment procedures etc. The

Valedictory Function of the Health PhysicsTraining Course 15th Batch: a report

changes were based on the feedback receivedfrom the faculty and the trainees and under theexpert guidance of the apex committee and wasessentially required, to bring up this training tomeet the growing needs of our department andmaintaing our training programmes withinternational standards.

He expressed happiness over the fact thatpresently the Health Physics training programmewas acknowledged by other Divisions of BARCand that HPD had extended guidance andassistance to others when it became mandatoryin BARC that all recruitments of technical staffshall be through formal training schemes only.

He noted that a large number of faculty andsenior officers were associated with the trainingprogramme and that Health Physics Division hadreceived whole-hearted cooperation from anumber of Officers in arranging the practicalsand the On-the-Job Training at differentfacilities. He attributed the success of thetraining programme to the combined efforts ofall Divisions of HS&EG. He congratulated allthe 35 trainees for their excellent performanceand welcomed the youngsters.

Dr. D. N. Sharma, Associate Director, HS&EGwhile addressing the gathering, congratulated thetrainees for their hard work which has resultedin their excellent performance in the course andenabled them to score additional increments inthe Scientific Assistant grade at the time ofabsorption. He called upon them to continue theirstudies and to get actively involved with theongoing programmes of the department. On thisoccasion, he recalled his continuing associationwith the training programme for the past few



years from the process of selection of thetrainees to their final absorption interview.

In his presidential address, Dr. A. K. Ghosh,Director, HS&EG observed that the objectiveof the training programme was to give thecandidates an in - depth awareness on thesystems, procedures and technical aspects. Itwas also required to prepare them to adopt ascientific approach to the tasks assigned, toinculcate an analytical attitude in solvingproblems and to develop the required skills intheir respective field of work. He appreciatedthe structure of the training programme and thesyllabus, covering a wide variety of subjectsincluding basic sciences, nuclear engineering andnuclear fuel cycle facilities.

He also expressed his happiness at theencouragement received from the AtomicEnergy Regulatory Board for this training course

through the ‘AERB awards to the merit holders’which is given to the 1st and 2nd rank holders ofeach batch.

In the valedictory address, the Chief Guest, Dr.S. Kailas, Director, Physics Group stressed onthe importance of formal training to make oneselfunderstand the concepts of nuclear andradiological safety aspects and also to have aclear awareness of the systems. He appreciatedthe efforts of Health Physics Division to impartprofessional training to the graduates in thisspecialized discipline and to make themcompetent to shoulder the responsibility ofensuring radiological safety in the nuclearfacilities. He also congratulated the HealthPhysics Division for their efforts in building upa full-fledged infrastructure for carrying out thetraining programmes uninterruptedly for the last20 years. The function concluded with a vote ofthanks by Mr. R.G. Purohit, Head, ORPRS,HPD.

Chief guest, Dr. S. Kailas addressing the gathering. Seated from left to right are Dr. P. K. Sarkar, Head,Health Physics Division, Dr. A. K. Ghosh, Director, HS&EG, Shri R. Bhattacharya, Secretary, AERB, Dr. D. N. Sharma,Associate Director, HS&EG and Shri R. G. Purohit, Head, ORPRS, HPD



It was on 28th February 1928, that the greatIndian Physicist Sir C.V. Raman discovered theRaman Effect, while working in the laboratoryof the Indian Association for the Cultivation ofScience, Kolkata. He received the Nobel Prizein Physics in 1930, for his work on the scatteringof light and for the discovery of the effect namedafter him. This day is of great importance forthe Indian scientific community and is celebratedall over the country every year, as NationalScience Day.

The Scientific Information Resource Divisiontook the initiative of celebrating the NationalScience Day at BARC. It was celebrated on28th February, 2011, at the Central Complexauditorium. As part of the programme, thefollowing events were organized.

National Science Day Celebrations at BARC

1. Fusion Engineering Exhibition: TheInternational Thermonuclear ExperimentalReactor (ITER) is one of the mostambitious programmes which waslaunched in 1985, to develop Fusionenergy as a viable energy alternative andto harness it for peaceful purposes. Indiabecame a member of this internationalcollaborative activity in 2005. A numberof R&D projects are currently beingcarried out in various Divisions of BARCas well as in other DAE units. Theexhibition gave a flavour of all these globalactivities through posters, publications andaudio-visual presentations.

2. Homi Bhabha Pavilion: The life and thework of Dr Homi Jehangir Bhabha wasportrayed through a series of posters. It

Dr. Srikumar Banerjee, Chairman, AEC inaugurating the Fusion Engineering Exhibition



was a fitting tribute to this great visionaryon this day, who pioneered thedevelopment of nuclear energy in Indiaand laid a firm foundation.

3. BARC Technologies: R&D spinoffs:Over the years, BARC has developed alarge number of technologies, some ofwhich have even been transferred tovarious private firms for industrialproduction. All these technologies wereshowcased in the form of posters. BARCScientists and Engineers who wereinvolved in the development of thesetechnologies, were present on theoccasion, to interact and explain thesignificance of these technologies.

All the three exhibitions of one month durationwere inaugurated by Dr. Srikumar Banerjee,

Chairman, Atomic Energy Commission. Dr.Banerjee showed keen interest in the exhibits.Dr. K. Bhanumurthy, Head, SIRD extended awarm welcome to all the invitees and colleagues.Dr. A.K. Suri, Director Materials Group,BARC, introduced the Chief Guest, Shri S.K.Sharma, Former Chairman, AERB. Dr.Banerjee gave an invited talk on “Order andChaos”. On this occasion, a compilation ofR&D publications of Dr. Srikumar Banerjee,both in the form of hard copy volumes as wellas a CD, (compiled by SIRD) was released bythe Chief Guest. Shri R.K. Singh, Head,MR&PAS, SIRD gave a vote of thanks.

Dr. R.K. Sinha, Director, BARC also visitedthese exhibitions on the 4th of March, 2011 andappreciated the effort. About 600 scientists andengineers have visited these exhibitions so far.

Dr. R.K. Sinha, Director, BARC at the Fusion Engineering Exhibition, Dr. A.K. Suri, Director, Materials Group andDr. K. Bhanumurthy, Head, SIRD can be seen with him.


BARC Scientists Honoured

Name of the Scientists: Mr. N.K. Goel, Virendra Kumar, Y.K. Bhardwaj and S.Sabharwal

Radiation Technology Development Division, Radiochemistry and Isotope Group

Title of the paper : “Radiation synthesized stimuli-responsive HEMA-co-MAETC hydrogels”

Award : Best Poster presentation award

Presented at : 3rd Asia Pacific Symposium on Radiation Chemistry (APSRC-2010) and

DAE BRNS 10th Biennial Trombay Symposium on Radiation and Photochemistry

(TSRP-2010)” held at Lonavla during September 14-17, 2010

Name of the Scientist : Mr. S.K. Lalwani, Electronics Division

Award : “NDT Achievement Award-2010” for his outstanding contributions

to “R&D in NDT”

Awarded by : Indian Society for Non-destructive Testing (ISNT), Mumbai chapter

Name of the Scientist : Ms. Shagufta Shaikh, Medical Division

Title of the paper : “Bull’s Multirule Algorithm, An Excellent means of Internal Quality Control for Hematology

Analyzers”

Award : Best Paper Award 2nd prize

Presented at : AIIMT 20th Congress of Bio-Medical Laboratory Science held at Tiruchirappali,

Tamil Nadu during Dec. 18-19, 2010

Name of the Scientist : Dr. B.N. Jagatap

Outstanding Scientist & Head, Atomic & Molecular Physics Division

Honour : Elected unanimously as the President, Physical Sciences Section of the 99th Session of

Indian Science Congress

: 99th session of Indian Science Congress will be held at Bhubaneshwar during

January 03-07, 2012, to be jointly organized by Kalinga Institute of Industrial Technology

(KIlT) and National Institute of Science Education and Research (NISER).

Name of the Scientist : Dr. H.S. Misra, Head, Molecular Genetics Section, Molecular Biology Division

Award : “B. S. Sarma Memorial Award- 2010” for his outstanding contributions in Biological

Chemistry and Allied Sciences

Awarded at : 79th annual meeting of the society held at Indian Institute of Science, Bangaluru. organized

by the Society of Biological Chemsists of India.

jan feb11 cover final 11-4

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