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11

RESEARCH AND DEVELOPMENT ACTIVITIES OF THE

HIGH PRESSURE PHYSICS DIVISION

for the period

March 1991 - September 1993

Edited by

B. K. Godwal :ind Y. S. Bluidauria

High Pressure Plmio. Division

1993

BARC/1993/E/03G

ooUJ

gj GOVERNMENT OF INDIA- ATOMIC ENERGY COMMISSIONUat, •

RESEARCH AND DEVELOPMENT ACTIVITIES OF THE

HIGH PRESSURE PHYSICS DIVISION

Edited by

B.K. Godwal and Y.S. BhadauriaHigh Pressure Physics Division

BHABHA ATOMIC RESEARCH CENTREBOMBAY, INDIA

1993

BARC/1993/E/03©

BIBLIOGRAPHY DESCRIPTION SHEET FOR TECHNICAL REPORT

(as per IS s 94OO - 1980>

01 Security classication :

02 Distribution :

03 Report status :

04 Series :

05 Report type :

06 Report No. :

07 Part No. or Volume No. s

08 Contract No. :

1O Title and subtitle :

Unclassified

External

New

BARC External

Technical

BARC/1993/E/O3O

Research and development activities ofthe High Pressure Physics Division forthe period March 1991 - September 1993

11 Collation :

13 Project No. :

2O Personal author <s> s

64 p.

B.K. Godwal; V.S. Bhadauria (eds.)

21 Affiliation of author <s) : High Pressure Physics Division,Bhabha Atomic Research Centre, Bombay

22 Corporate author(s) : Bhabha Atomic Research Centre,Bombay-400 085

23 Originating unit :

24 Sponsor(s) Name :

Type s

30 Date of submission :

31 Publication/Issue date

High Pressure Physics Division,BARC, Bombay

Department of Atomic Energy

Government

October 1993

November 1993

corttd. . . (ii)

40 Publisher/Dist.-ibutor i Head, LiDrary and Information Division,Bhabha Atomic Research Centre, Bombay

42 Farm af distribution : Hard Copy

50 Language of text : English

51 Language of summary J English

52 No. of references :

53 Given data on t

6O Abstract : The research and development activities of the HighPressure Physics Division during the period March 1991 to September1993 are reported in the farm of abstracts and titles of thepublications. The report is organised into two sections: (A) HighPressure Physics Section, and (B) Seismology Section. A list of staffmembers of the two sections is also given.

70 Keywords/Descriptors : VERY HIGH PRESSURE} HIGH PRESSURE; PHYSICS;SEISMOLOGY; BARC; RESEARCH PROGRAMS; EARTHQUAKES; PHASETRANSFORMATIONS; METALS; ALLOYS; EQUATIONS OF STATE; SHOCK WAVES;LASERS; X-RAY DIFFRACTION; REACTOR SITES; SEISMIC WAVES; PROGRESSREPORT; SITE CHARACTERIZATION

71 Class No. : INIS Subject Category s B2242; B2442; B314O

99 Supplementary elements :

FORHASD

The High Pressure Physics Division was formed on March

1, 1991. This report is an account of the work done by the

staff of this division since then.

The High Pressure Physics Division is organised into

two sections: (1) High Pressure Physics Section and (2)

Seismology Section. The basic research and development ac-

tivities of the two sections are:

(a) To carry out experimental and theoretical investigations

in the fundamental aspects of the cohesive properties of

condensed matter under ultra high pressure and

(b) To carry out R&D in experimental and theoretical Seis-

mology with special emphasis on continuous operation of

seismic arrays at Gauribidanur and Delhi for seismic source

discrimination.

Some of the areas of research are:

1. Investigations at ultra high static pressures using in-

digenously built diamond cells by X-ray and optical tech-

niques of the phase transitions in (a) metals and alloys and

(b) the amorphization under pressure.

2. Investigations at shock pressures of the equation of

state and the kinetics of phase transitions of materials by

a single stage gas-gun and lasers.

3. Theoretical investigations of equations of state and

phase transitions (structure and kinetics) by electron

theory methods.

4. To develop hydrodyn'amic codes for studying the effects of

shock waves on materials.

5. Seismic source discrimination by using data recorded at

Gauribidanur and Delhi seismic arrays.

6. Instrumentation development for continuous and uninter-

rupted seismic monitoring and to generate high quality seis-

mic data.

7. Operation of the radio telemetered seismic network at

Bhatsa.

8. Microearthquake monitoring at nuclear power plant sites.

The present progress report covers the period upto

September 1993 and the format adopted appropriately repre-

sents the R&D character of the Division.

S.K.Sikka

Head, High Pressure Physics Division

Bhabha Atomic Research Centre

Trombay, Bombay.

CONTENTS

A. High Pressure Section

Page

1. Papers in Journals

2. Papers in Conference Proceedings

3. BARC Reports

4. Only abstracts in Conferences

5. Books/Journals edited

B. Seismology Section

1. Papers in Journals ' 3 1 - 3 4

2. Papers in Conference Proceedings 35 - 38

3. BARC Reports 39 - 42

4. Papers published in Hindi 43 - 47

1 -

14 -

25 -

28 -

13

24

27

29

3 0

A(l). PAPERS IN JOURNALS

CURRENT SCIENCE, VOL.60, N0.7, 10-APRIL 1991 , pp 397-40B

Reprinted from Current Science GENERAL ARTICLES

L. Frontiers in high-pressure physics researchR. Chidambaram and Surinder M. Sharma

Studies of materials and the discovery of various novel and unexpected phenomena under highpressures have contributed immensely to our understanding of the behaviour of matter. The varietyof phase transitions observed display systematic patterns, giving insights into the underlying physics.There are many similarities and significant differences in the phenomena observed under static anddynamic (shock) pressure loading. This article presents experimental and theoretical developmentsin this fascinating field.

Vollumel 52. number 7 , pp 397-408 PHYSICS LETTERS A 28 January 1991

2. A tetrahedrally close packed (tcp) structurefor the high pressure phase of potassium

V. Vijayakumar, S.K. SikkaHigh Pressure Physics Section. Purnima Labs. BARC. Bombay 400085. India

and

H. OlijnykBayensches Forschungsinstilut filr Experimenlette Geochrmie and Geophysik, VniversitSt Bayraith. W-S5S0 Bivrrulh. Germany

Received 20 September 1990; accepted for publication 18 November 1990Communicated by J.I. Budnick

A structural model of the high pressure phase of potassium above 20 GPa is proposed based on the idea of Pauling thai theaverage ligancy of atoms in metals should increase under pressure. It is shown that a body centered cubic unit cell (with 81 atom*in th« primitive unit) of MgM( AlZn )4 , type fits the d spacing* of the X-ray diffraction patterns of potassium in this phase.

Bull. Mater. Sci., Vol 14. No. 5. October 1991. pp 1213 1218. C Printed in India.

3 . Visual observation of phase transitions in LiKSO4 under pressore

HEMA SANKARAN*. S K SIKKA, A SEQUEIRA» and BFURSENKO**High Pressure Physics Division. 'Solid Slate Physics Division. Bhabha Atomic ResearchCentre. Trombay, Bombay 400 085. India"Institute of Geology and Geophysics. Novosibirsk. USSR

MS received 23 April 1991: revised 20 July 1991

Abstract. Phase transitions in LiKSO4 have been visually observed in a diamond-antilcell up to 16GPa. The observations confirm a symmetry change at 0-9 GPa and a solid-state crystal to amorphous transition at 12 GPa. The crystal exhibits a memory across thecrystalline transitions. Interesting microstruclural features were observed in the range ofthe amorphous phase.

Keywords. High pressure; diamond-anvil cell; LiKSO4; phase transitions; pressure-induced amorphualion: visual observations.

Bull. Mater. Sci., Vol. 15. No. 1. February 1992, pp. 35-46. © Printed in India.

4.Behaviour of materials under shock loading conditions

S K SIKKAHigh Pressure Physics Division, Bhabha Atomic Research Centre; Bombay 400085. India

Abstract Shock wave research it a multidisciplinary field. In materials science, it is usedto study equalion-of-state, phase transitions and mechanical properties. In material processing,synthesis, powder compaction, shock sintering, shock welding etc have been the prominealapplications. We have been doing shock wave research at Trombay during the bit twodecades. Recently, we have built a single-stage gas gun to generate shock pressures in samples.In this paper, we describe this facility and some work done on the interpretation ofshock-induced phase transitions.

Keywords. Shock loading; phase transitions; behaviour of materials; single-stage gas gun.

PHYSICAL REVIEW B VOI.UMI- 4». NUMIU-.K 2, pp J 795-1798 15 JANUARY

5. Theory of high-pressure phases of I'b

Amy Y. I in. Alberto (i:ni-|;i. iintl Mnrvin I.. ColtenDepartment of Physics. University "j' Ciilituniiu m Rvrkelry. Berkeley. California 94720

and Materials and Chemical Sciences Division. Lain nice Berkeley Laboratory. Berkeley. California 94720

B. K. Godvval* iiiul Raymond Jc;iiilc>7Department of Geology and Geophysics. Unirersity <>/ California at Berkeley. Berkeley. California 94720

(Received 5 February 1990: revised manuscript received 27 July 1990)

We have studied the behavior of I'b ;il hiiili pri-sMiie using the lirsl-principles pscudnpotcntialtotal-energy method, with spin-orbit eflccK uc.ifi.-il uilliin pert million theory. Our calculationsagree with recent experiments that indicate tliiit I'b undergoes a phase transition lo the bec struc-ture at pressures on the order of 100 GPa.

* High Pressure Physics Division, BARC, India.

PHYSICAL REVIEW B VOLUME 44, NUMBER 10, pp 4872-4876 | SEPTEMBER 1991-11

6 . Nonequilibrium shock behavior in quartz

A. Ng. B. K. Oodwal,* J. Wnlerman, and L. DaSilvaPhysics Department, University of British Columbia. Vancouver. British Columbia. Canada V6T2A6

N. W. AshcioftLaboratory of Atomic and Solid State Physics, Cornell University. Ithaca, New York 14833-2501

R. JeanlozDepartment of Geology and Geophysics, University of California, Berkeley. Berkeley, California 94720

(Received 9 April 1991)

Observations of the formation and propagation of a laser-driven strong shock in fused and a-quartzreveal anomalously high, transient shock velocities. These results disagree with calculations bated onequilibrium equations of state. It is conjectured that at the shock front, a transformation of quartc tostishovite is preceded by shock-induced disorder accompanied by a significant entropy increase. Thisstate remains dominant until sufficient relaxation has occurred.

* High Pressure Physics Division, BARC, India.

-3

NATURE VOt 3*9 • 21 FEBRUARY 1991 f pp 6 8 7 - 6 8 9

?. Static strength and equation ofstate of rheniumat ultra-high pressuresRaymond Jaantoz, B. K. Godwal* ft Charfes Meadat

Department o« Geoloev end Geophysics. University of California. Berkeley.CaMorria 9 4 7 2 0 , USA

YIELDING of materials Is not understood well enough for detailed,quantitative predictions of strength to be possible except J»y usingscmi-cmpirlcal models1'1. Studies of material strength at highpressures arc therefore of fundamental as well as practical latemlfor determining the relationship belncea strength and other ahy-ttcal properties*"*. To this end. we have measured the shear stress( T ) supported by rbealum at pressures of up lo 120 GPa, far higherIbaa the pressures used in previous studies. Rhenium i* of par-ticular Interest because it has the highest known bulk and shearmoduli among metallic elements7"*. By using two independentmethods of determining shear stress at room temperature, we findthat rhenium is one of the strongest pol) crystalline materials"Inresllgated so far, with shear stresses at high pressures reachingT//I =s0.04(±0.02) relative to the shear modulus p. These valuesof t//t are nevertheless compatible with current theoreticalexpectations, indicating that the high strength of rhenium is notanomalous1'3'*.

* High Pressure Physics Division, BARC, India.

8. HIGH PRESSURE PHYSICS RESEARCH ATIt A IK

K CHIDAMBARAM

liluthlni Miunu Ri-uunh Centre. Tnuiihiiy. Bumhay 4(Kt085. India

«..,»../ l/jfij / . IW2

High prc»urc pli>sic> U-SC.IKII iii BAKf spans a pviuul ormoic than two decades and covers the area ofbuth staiic uiul ilvii.nnn. piosurcs on (he one hand ami Iwiih iheureiicul and c*perimcnlal aspects on theolhci I'tic cupcnineiiial faciluivs .iv.iil.ihlc ntcliult Ili.uiituiil Anvil fell* for X-rmy diffiaclion and Raman$pci.iii>M.i>p) anJ a lielii !?.i> e1"' •'"••="•• iraii%liiiiiwi««m invctfigdicd in mclullic systems include those in(M ll|!. tiitiiMiiiin niculs. i i ic c.iiilis ami .UIIIIKIO ami these in\»ligdliuii» ha*« been supported byilviailcJ KHUI -.iiiuiuiu- i..ilci/l..ii..ii> .mil Minlio >l ilu- mcclMitiMti of pluiw tiansliunHliuns. E«lcnsi«

' cHiidi!..n <•! -.idle sunlit-, ovci a «i«lc idiiyc •>! |UCMIIK-% nivliiJc J lieu im«lcl l«»r the intermediate pressureMiigc iviHci-n I' •> diul It' I I'd dml ihitMpici.iiton Hi'cxiwiinienlal slunrk ilugomuts.

Kl-Y W t i U O S Ilijili pu-«inf . \limli ».ivi>. |ili.i*c naiiMiitnis. JS.MI.CIHI

PHYSICAL REVIEW B VOLUME 46, NUMBER 9 , pp 5 7 8 0 - 5 7 8 2 I SEPTEMBER I9*M

9. Thorium: A 5/4>and metal at ultrfthigh pressures

R. S. Rao, B. K. Godwal. and S. K. SikkaHigh Pressure Physics Division. Bhabha Atomic Research Centre, Bombay 400065. Mia

(Received 21 January 1992; revised manuscript received I May 1992}

The electronic structure of thorium is computed to study the recently reported (Phya. Rev. Ut t . «?,3563 0991)) high-pressure fcc-bcl structural transition. We Rnd that elemental thorium is MMQM ia thatunoccupied / levels become populated at ultrahigli pressures, with the l-crmi level intercepting t h e /band at a volume fraction of 0.6. The total energies show that the resulting occupation o f / baadt byabout I electron drives the fcc-to-bci transition near 80-GPa pressure, and thorium then mnstbki Ihc/-band metal cerium. The ftp electrons must ue treated as band states in estimating the traasMioa pro-ture and 0-K isotherm.

PHYSICAL REVIEW BCONDENSED MATTER

THIRD SERIES, VOLUME 46, NUMBER 22 , jp 4 3 5 9 - 4361 ' DECEMBER I«2-n

10 • Distorted hep structure of zinc under pressure

S. Meenakshi, V. Vijayakumar, B. K. Godwal. and S. K. SikkaHigh Pressure Physics Division, Bhabha Atomic Research Centre, Bombay 40008S, India

(Received 27 February 1992; revised manuscript received 6 July 1992)

Results of c /a variation under pressure for zinc from total-energy calculations that use •rst-principkslinearizcd-muffin-lin-orbital calculations are presented, c/a decreases with compression and is (band 10change slope around K/P 0 =0.92 , to approach the ideal value of c/a «1 .63 . This behavior Is compare*with,existing experimental data and with full-potential linearized-iugmenied-pltne-wave calculations.

McdHKturnmikcMMMkn rmtmt m H» Ifm—t * • » > • •iH pmww* fcj kcmr oiuy

11. GOLD UNDER HIGH PRESSURE

B. K. GODWAL

High Pressure Physics Division, Bhabha Atomic Research Centre. Tromboy.

Bombay 400085, India

A. NG

Physics Department, University of British Columbia, Vancouver. B.C.. V6TIZI.

Canada

RAYMOND JEANLOZ

Department of Geology and Geophysics. University of California. Berkeley. 94720.

U.S.A.

(Received April I. 1992)

First principle predictions for the equation of state of gold using solid and liquid Mate theories arecompared up to combined pressures and temperatures of 600GP* and I7000K with static diamond anvilcell compression, ultrasonic measurements and shock Hugoniot data which include a recent laser drivenshock Hugoniol points at 600 GPa. Excellent agreement between theoretical and experimental data ifobserved. The theoretically estimated 300 K isotherm agrees to within 2 GPa with the isotherm that hasbeen measured to 70 GPa using the diamond anvil cell. The structural energy estimates show that thenormal f.c.c. phase remains stable under pressure. The estimate of the shock Hugoniot tempefaturc of goldat 600 GPa based on a liquid state model is consistent with the measurements of laser induced shockluminescence, which in fact provides an experimental determination of the temperature of gold above itsHugoniot melting point. The powerful means provided by theory in the prediction of material propertiesof gold at ultra high pressures and temperatures is significant because gold is an efficient converter of laserenergy into soft X-rays and is a potential candidate as a standard for high pressure, high temperature work.

KEY WORDS: Gold, high pressure, diamond anvil cell, isotherm, shock. Hugoniot.

HUH »rUurr # « « « * . 1992. Vol 10. pp 74J-746 O l » 2 Gocdo. » d Bract SoRcprina available directly from ihe publisher VtnMt mPhotocopying permitted by IHXIKC only

12. INTENSE LASER INDUCED SHOCKGENERATION IN GOLD TARGETS

TARA DESAJ, B. K. GODWAL* and H. C. PANT

Laser and Plasma Technology Division, *High Pressure Physics Division, BhabhaAtomic Research Centre. Bombay 400085 India

(Reeeiml April I. 1992)

Experiments carried out demonstrate the production due to soft X-ray* of enhanced ablation pressure Thetargets used were plumir gold foils. Aluminium targets were ulso used to demonstrate the relative effect.

KEY WORDS: Gold target, target interaction, laser beam.

«<t» rrtumt lUutfk. IW, Vol 10. p> »l-J0» t> i»M ( M M «rt *M«a SeaMt fMNWtaM, tA .Rcpnms mitabk Aranly frw. Iht pubKthti . . . • . . . . — .Pkoiocoptiltf pcrmiunJ by kcnw only

13. ON THE OCCURRENCE OF b.c.c.-h.c.p.STRUCTURAL PHASE TRANSITION IN Mo

UNDER PRESSURE

S. K. SIKKA, B. K. GODWAL and R. S. RAO

High Pressure Physics Division. Bhabha Atomic Research Centre, Trombay,Bombay 400085. India

(Received April I. 1992)

To resolve ihe controversy on the occurrence of a b.c.c.-h.c.p. tra.-^ilinn in shock ac wdl at Mattemeasurements in Mo, ve have done more accurate total energy electronic structure calculations. Ourlesulls show that this phase transiiion should occur al much higher pressures than suggested by earliercalculations.

KEY WORDS: Phase transiiion. shock and static pressures. Mo.

Metals Materials And Processes, 1902. Vol. .?, No. 4, pp 303-308© Meslmp Science Publishers, Bombay, India.

14. ON GLASS FORMATION UNDER PRESSURE

S.K. S-kka'.Pressure Physics Division

iihahhti A atomic Research CentrvTromhny,Bombay 400 0H5, India

ABSTKACTi Pressure induced glass formation has l>ccn observed so far in SIUHI 30 Mihslaaccs. la lai* paper.ihc thermodynamics, the driving mechanisms and Mruclural aspects of the crystal lo amorphous iraasilMMS arereviewed.

Key words: Glass, l-'ormalion. Pressure. Thermodynamics, amorphous transitions.

link raw Hilton*. IV. VVI 10. pp T»S ?*» r l«ii liantomtml mnnttStxmx f m i n i . XARc|>nnl> awtUtilc dirctlly hum Ike publtUKf Tn*t4 m lie trawl U-mfiimrtu>wci>p)inj[ prnnittnl h> tuvav oal>

15. HIGH STRAIN RATE RESPONSE OF ANELASTOMER

SATISH C. GUPTAt and Y. M. GUPTA

Shock Dynamics Laboratory. Washington Stale University. Pullman.WA 99164-2814. U.S.A.

I Received April I. 1092)

Plale impact experiments have been performed to examine the high strai:i rate response of an elastomer(explosive binder) shocked to Kkbar stress. Particle velocity data have been obtained using in-materialelectromagnetic velocity gauges. Normal impact experiments have provided compression and release wavevelocities and stress-strain results: ramp wave experiments indicate that the elastomer response a indepen-dent of loading rate: inclined plate impaci measurements show that the material does not support any sheareven at these strain rates. Additionally, numerical simulations have been performed to show that shockpropagation in viscous fluids can be simulated without artificial viscosity but !>y using the material viscosityin the constitutive relations. Such simulations will be useful in ob.aining miterial viscosities from themeasured wave profiles.

KEY WORDS: Shock wave, elastomer, viscosity

Japanese Journal of Applied Plysics (1992)

16. Structural Studte* on Se and Te with Synchrotron Radiationto Hegabar Presaurea

W.B. HOLZAPFEL. T. KROGER*. V. SIEVERS mtd V, VIJAYAXUMAR**

Unlveraltat-CII-Ptderborn, FachberMr.li Diyilk. PostfachlS ?'.D-479& Paderborn, Germany

By the use of energy dlsperalva X-rny Hlffrnctlon with synchrotron radiation, prcatttr* Imhicedstructural phase transition!* and «qitnti<itii of tttntr ufrr articlled on 5a end T» In the •xtrnrladlprcaiur* ranga up to 129 C!PB. In mnt rnnt: to n previous nturly on 3e to 50 OPa, the hl^hnrresolution with aynchrotron rndlntlnn In the 'present ntudy allowed for an Mnmablauou*tdenclfleatlon of the atructurv for Sx IV n.i rtenbohrdral (K-Po-type) with one atoa In therhombohedral unit cell, and thus, a rio««i ntnllarlty to T» under pranaura ami to «t highertenpetaturaa la reeitabllahvd.

High Pressure Physics Division, BARC, India.

Jjny%.. Condeiu. Matter 4 (1992) UU-U& Printed ui the UK

LETTER TO THE EDITOR

16. The low-temperature phase of sodium: an intermediateorthorhombic distortion?

Hema Sankaran, Surindcr M Sharma and S K SikkaHigh Pressure Physics Division. Bhabha Atomic Research Centre. "Bombay. Bombay

400QBS. India

Received 13 November 1991

Abstract. We have shown through flrst-principks total-energy calculation. ° V ° * " "That a. low temperatures .here is , neariy-zero barrier path ««"*»"»£*£££deformations leading from the body-centred cubic (BCC) to the - o r e stable ******close-packed (HCP) structure. The observed diffraction patterns ****»>* « £ » « «without the aid of stacking faults that are needed lo account for dewations f r o - Ikecalculated pattern if a 9R structure is assumed.

High Frasvre Ritrarch. 1992. Vol. 10. pp 675-O80 f • 199? Gordoa aad Ireack Sana PybMton. S ARepnnls available direct!* from the publisher PnaucJ M tfv UMed KwfrfcwiPhotocopying petmmcd by license anly

1 7 . AMORPHIZATION UNDER SHOCK LOADING

S. K. SIKKA and SURINDER M. SHARMA

High Pressure Physics Division, Bhabha Atomic Research Centre. Trombay,Bombay 4(XkQ85. India

(Received April I. I9tl)

The problem of crystalline lo amorphous (r — a) phase transformation, in the context of shock loading.is analyzed. The studies under static pressures show that beyond the stability field of the ambient phase.an amorphous phase may be realized if the kinetic conditions are not favorable to the accessibility ofequilibrium phase of higher coordination. The examination of shock results of some of these substancesreveals that '.he so-called "mixed phase" region begins at the pressures which are same as that occ — atransformation in the static experiments. Further the Hugoniol temperatures at these pressures are farlower than required for the realization of the hgh pressure crystalline phase. From these observation* aswell as from an understanding gained through static experiments, we infer that these materials amorphtttunder shock loading. The analysis indicates that the existence of hot-spots is not essential to the formationofdiaplectic glass. Instead, it seems to emerge directly rrom the solid-solid phase transformation, adequate-ly aided by Favourable kinetic conditions.

KEY WORDS: Amorphization, shock waves, quartz.

Reprinted from Current Science RESEARCH ARTICLES

CURRFNT SOI-NIT. VOL 6«. NO <>. ?< SI I ' l l MM R I W , p p 3 1 7 - 3 2 0

Close packing and pressure-inducedamorphization

S. K. Sikka and Surinder M. SharmaHigh Pressure Physics Division. Rhubha Atom't Research Ccnlrc. Bombay 4000X5. India

Recently a large number of crystalline compounds havebeen discovered to amorphize at high pressures. However,the molecular origin of this transformation is not under-stood. In this article, we show that this is aconsequence of a competition between the close-packingand long range order—a principle well known in organiccrystallography. We show that the tendency of thesesystems to acquire higher coordination under compression issterically hindered at some pressure due to the strongnature of inter-molecular bonding of building blocks.This hindrance drives the system to sacrifice the trans-lalional order to achieve better packing. The applicationof principle is shown through the examples of Ca(OH)2,S i O . ice, LiKSO4, etc.

PHYSICAL REVIEW B VOLUME 47, NUMBER 5, pp 2878-2881 1 FEBRUARY 1993-1

19. Total-energy calculations for crystalline approximants of quasicrystalline structures:Occupation of the centers of the icosahedral units

S. K. Sikka and Surinder M. SharmaHigh Pressure Physics Division, Bhabha Atomic Research Centre, Trombay, Bombay, 400085 India

R. ChidambaramHigh Pressure Physics Division, Bhabha Atomic Research Centre, Trombay, Bombay, 400085 India

and Jawaharlal Nehru Centre for Advanced Sciences, Indian Institute of Science Campus, Bangalore, 560 012, India(Received 16 March 1992; revised manuscript received 6 July 1992)

,Motivated by recent positron-annihilation experiments on quasicrystalline materials, we have investi-gated whether the centers of packing units [of Mackay's.icosahedron for the Al-Mn system and cuboc-tahedron Tor the Mg-Z.ii (AD system] arc empty or Tilled. Our pseudopotential-based total-energy calcu-lations suggest that the centers arc occupied, in agreement with experimental positron-annihilation re-sults. Possible reasons for discrepancies with the diffraction results are discussed.

10

PHYSICAL REVIEW D VOLUMI- 47. NIJMilER 10 , 5 7 1 0 - 5 7 1 4 I MARCH 1993

20. Moleculflr*dynamlc0 ttmulatlon of pressure-Induced crystalllnc-to-amorphous tramlttoain tome corner-linked polyhedral compounds

S. L. ChaplotSolid Stale Physics Division. Bhabha Atomic Research Centre, Bombay 40008$. India

S. K.SikkaHigh Pressure Physics Division, Bhabha Atomic Research Centre. Bombay 400085, India

(Received 30 April 1992; revised manuscript received 21 September 1992)

Molecular-dynamics calculations are carried oul on quartz, AIPO4, ami LiKSO<, which arc composedof corner-linked tetraliedra and arc known to display crysialline-to-amorphous transitions at IS, 12, and13 OFa, respectively, at 300 K. The transition occur* when the 7",O7", angle IT, =Si.AI.Li; Ti^SiJPfiiis near 124', and the nearest oxygen atoms approach within their van tier Waals separation distance.Consequently some of the cations acquire a higher coordination. The existing experimental data are toagreement with these results. A qunsihnrnionic bllicc-dyiiamical calculation as a functirn of pressuresuggests a zone-boundary plionon instability prior to the phase transition.

1. Fbyi.: Condau. Matter 5 (1993) 6345-4356. Printed in the UK

21. The behaviour of a-quartz and pressure-induced SiC>2 glassunder pressure: a molecular dynamical study

M S Somayazulut. Surinder M Sharmat, Nandini Gargj. S L Chaplot} andSKSikkaft High Pressure Phyaics Divition. Bhabha Atomic Research Centre. Bombay 400 0>S. Indkt Solid Stale Physici Division. Bhabha Atomic Reaearcfa Centre, Bombay 400 085. India

Received II March 1993. in 6na! fonn 13 May 1993

Abstract. We have carried oi l extensive molecaUr dynamical calculation* on a-qoartx aadpre*>uie-ioduced glau and have related these to the experimental obteivationi under Made aad•hock preiiure loading. In the ciyitalline quartz, deniification and amorphizatioo lake placeiharpiy around 20 GPa and are related to the change* in tbe Si coordination. The u n i w a -induced glau ii considerably lesi compreniUe than tbe filled tilica, aVnmng a gradual chanfsin the Si coordination, and ii unlike the glau studied earlier by Tie, Khig and Le Page. Howevereven this g lut shows a densification. similar to that of quartz ai well as fused silica. Retmwalof the four-coordinated stale, in both cases, requires annealing at high temperature*. Just befbraamorpfaiation of cr-quartz, O atoms are still far from the recently proposed ace packaig.

11

J. Phy*.: Coodens. Matter S (1993) 4557-4562. Primed in (he UK

22. Raman spectroscopy studies on the orthorhombic-to-rhombo-hedral transition in thallous nitrate

M S Somayazuluf, A P Royf and S K DebJt High Pressure Physics Division. Bhabhi Atomic Research Centre, Trorabay, Bonbay400085. Indiat Solid State Physics Division. Bhabha Atomic Research Centre. Trombay. Bombs? 400085,India

Received 31 July 1992. in final form II March 1993

Abstract The external modes of thallous nitrate have been studied as a taectkm of teapentwcfor oriented single crystals. Since the orthorborobic-»rhorabohedral tramilioa (Tm m 352 K) isirreversible, the spectra of both phases could be recorded at low temperatures for the sane crystal.Two distinct nitrate librational bands are identifiable in the orthorhorabic phase comcpoadiagto the two sets of nitrate ions. These are observed to be centred at 120 and I4S c m ' 1 at 100 K.Across the transition temperature, while the former remains unshifted, the band at 145 c a r 1 i iobserved to soften abruptly and in the rhombohedral phase it is alto found to occar at 119 cm' 1 .Structurally, this would therefore imply reorientation of one of the two sett of aitnte moiecalef.The enumeration of external modes in the rhombohedral phase rales out the possibility o f a w i icell with one formula unit per unit cell, as it has been assumed in the literature so far.

PHYSICAL REVIEW B VOLUME 47. NUMBER 17 , pp 1 1 4 9 1 -1 1 4 9 4 1 MAY I9M-I

23. Raman-scattering study of lilgh-pressuro phase trnnsition and emorphlzation of resorclnol

S. K. Deb, M. A. Reldia, and A. P. RoySolid Stale Physics Division, Bhabha Atomic Research Centre, Bombay. 400083 India

V. Vijnyakumar, S. Meenakshi, and B. K. GodwalHigh Pressure Physics Division, Bhabha Atomic Research Centre, Bombay, 400095 India

(Received 25 September 1992; revised manuscript received 23 November 1992}

Crystalline resorcinol [CtH4(OH)2] lias been shown to amorphize at 40 kban, tolely using Ramanscattering. The external modes vanish resulting in a spectrum similar to the density or states spectrum,but the internal modes persist indicating a breakdown of Iranslational and orientation*! correlation be-

^ tween the molecules. The amorphous state recrystallizes after the pressure is released. We also provideadditional information on the known a to/? phase transition.

12

PHYSICAL REVIEW I. VOI.UMK 47, NUMBER I , pp 487-489 I JANUARY W3 I

24 . Equation of state of iiriinltlvc-hvxtii:«iiiH| silicon and the effect or pressure onsome electronic properties of three high-pressure phases of silicon

A. NeclhiiiliigiiinjiiM*School of Physics, Madurai KummitJ Uniwrsiiy. Madura! 625 021. India

V. VijayakuinarHigh Pressure Physics Division, Bhabha Atomic Research Centre, Bombay 400OSS. India

(Received II February 1992: revised ntnituscript received 12 August 1992)

The linear muntn-tin orbital method, which is 8,,,,,| (or ulme packed structure. Is used to obtain pres-lure as a function of volume for the primitive howgcmal silicon by introducing empty spheres at voids tomtke it close packed I hi computed results me- in g.,(.(l nRtccmcnl with the experimental value*. IheThomas-Fermi screening pninniuicr, I'iinli spin susceptibility, ami Hie electronic heal capacity of theprlmilive-licxngunul, hep, uml Ice phases ..i sili. .,„ ,,,0 cult ulaled as ruuetions of pressure and possiblecomparisons are made.

CURRENT SCIENCE. VOL. 65. NO. 5. 10 SEPTEMBER 1993, p p 3 9 9 - 4 0 6

REVIEW ARTICLE

25. Predicting the high pressure phasetransformations using density functionalapproachSatish C. Gupta, Jyoti M. Daswani, S. K. Sikka and R. ChidambaramHigh Pressure Physics Division. Bhnhha Atomic Research Onlrc. nomhny 400 085. India

During the last decade, there has been an intense feed-back between high pressure experiments and theoreticaltechniques based on the density functional formalism forthe analysis of phase transformations. I his has resultedin increased accuracy in theoretical compiitnlions millthey have nnvv acquired predictive capabilities. Somesuccessful examples are discussed. The existing prob-lems and their possible solutions are indicnted.

13

A(2). PAPERS IN CONFERENCE PROCEEDINGS

SHOCK COMPRESSION OF CONDENSED MATTER 1991S.C. SCHMIDT. R.D. DICK. J.W. FORBES. D.G. TASKER (editors)e 1992 Elscvicr Science Publishers B.V. Ail lights reserved. " '

1 . BAND STRUCTURE CALCULATIONS TO PREDICT PHASE TRANSFORMATIONS AT HIGHPRESSURES

Satish C. GUPTA

High Pressure Physics Division, Bhabha Atomic Research Center, Bombay 400 085, India.

Predictions of pressure induced phase transformation in materials from ab initio methods are rare. This it becausethe Gibbs free energy differences between different phases are very small (a few mRy/atom or •mailer). However,recent band structural theories based on density functional formalism have acquired capabilities to calculate suchsmall energy differences due to the increase in computational speed and improvements in the theories. Oneexample of the successful prediction of pressure induced phase transformation is the hep to fee transition at 80GPa in Si and hep to bcc transition around 50 GPa in Mg. These transitions have been later verified usingenergy dispersive, x-ray diffraction (EDXRD) measurements in a diamond anvil cell (DAC). The other exampleis our prediction of pressure induced transitions in group IV elements (Ti, Zr, and Hf,) employing Linear MuffinTin Orbital method in conjunction with the Andersen force theorem. In Zr, we predicted a new phase transition,u (a three atom simple hexagonal) to 0 (bcc) at 11 GPa, in addition to the known lower pressure, a (hep) to utransition. This prediction was subsequently confirmed using EDXRD measurements and found to occur at 30GPa. A similar transition (u to (i) was predicted in Hf at 55 GPa which occurred experimently at 71 'GPa. Thecalculations on Ti, however, suggested that no u to j? transition occurs up to 26 GPa; this result also agreed withlater experiments. Furthermore, our analysis has successfully explained the causes of experimental shockdiscontinuities observed in these metals. Despite such success of the theories in predicting the pressure inducedphase transitions, there remains a problem of the need for the input crystal structures. Here, the densityfunctional molecular dynamics calculations may provide an answer.

SHOCK COMPRESSION OF CONDENSED MATTER 1'J'JIS.C. SCHMIDT, R.D. DICK. J.W. FORBES. DC. TASKER (editors)© 1992 Elscvier Science Publishers B.V. All rights reserved. 839

2.A SINGLE STAGE GAS GUN FOR SHOCK WAVE STUDIES

Satish C. GUPTA, R.G. AGARWAL, J.S. GYANCHANDANI, S. ROY, N. SURESH, S.K. I3IKKA, A.KAKODKAR and R. CHIDAMBARAM

Bhabha Atomic Research Center, Bombay 400 085, India.

For the last two decades, we have been investigating the equation of state and phase transitions in variousmaterials by first principle electron theory methods. In order to confirm some of the theoretical predictions, wehave now buijt indigenously an experimental facility for generating both static and dynamic pressurei on samples.For producing shocks, we have developed a single stage 62.8 mm gas gun. It is patterned after the WashingtonState University gas gun. A unique feature is a remote control unit which allows firing of the projectile in manualor auto mode. Both planar and inclined impacts can be obtained. We have developed instrumentation formeasuring projectile velocity, tilt of the impactor, shock velocity, particle vplocity and shock pressure profiles. Acomparison of the expected and measured projectile velocities shows ihat use gun is performing well. Somepreliminary compression experiments indicating the effect of shear on the a — u) phase transition in Ti will bereported.

14

Recent Trends in High Pressure ResearchXditor : A.K. SinghOxford & IBH Publishing Co.,1991

XIII AIR APT— International Confetrme on High Pressure Science and Trchnetaty. 1991, p p 2 5 4 - 2 5 8

3. PRESSURE INDUCED GLASSES

S.K. Sikka

High Pressure Physics Division. Bhabha Atomic Research Centre, TrombayBombay 400 085. India

Pressure induced glass formation has been so far observed Inabout 30 substances. In this paper, ye review thethermodynamics, the driving mechanisms and structural aspects ofthese crystal to amorphous transitions.

Keywords: Pressure. arorphisation, g iass . thermodynamics.

XIII AIR APT — International Conference on High Pressure Science and Technology. 1991 f pp 2 5 9 — 2 6 1

4. MOLECULAR DYNAMICS SIMULATIONS OF PRESSUREINDUCED CRYSTAL TO AMORPHOUS TRANSITIONS INSOME CORNER LINKED POLYHEDRAL COMPOUNDS

S.L Chaplot' and S.K. Sikka2

'Solid Slate Physics Division.'High Pressure Physics Division,Bhabha Atomic Research Centre, Bombay 400 085, India

Molecular dynamics calculation is carried out on quartz, A1PO+and liKSO , which are' composed of corner Jinked tetrahtdra andare known to display crystal to amorphous transitions a t IS, 12and 13 GPa respectively at 300 K. The t ransi t ion occurs whenTOT angle is near 12^^ , Some of the cations acquire a highercoordination.

Keywords : Molecular dynamics, amorphous transition

15

XIIIAIRAPT—Inttrnational Conftnnce on High PrtsnutStitncemidTtchwIoiy. 1991 f n o 3 3 5 - 3 3 7

5. THEORETICAL EQUATION OF STATE OF THE PRIMITIVEHEXAGONAL PHASE OF SILICON

A. Neethiulagarajan' and V. Vijayakumar*'PhysicsDepartment.VHNSN College.Virudnunagar6260C1.India

'High Pressure Physics Division. Bhabha Atomic Research Cenlre. Bombay 400 085.India

The linear muffin-tin orbital method which is gocdfor close packed structures is used to obtain thepressure as a function of volume for the primitivehexagonal silicon by introducing empty spheresat voids to make it close packed. The computedresults are compared with experimental values.

Keywords: High pressure phase, equation of state,silicon.

Recent Trends in High Pressure ResearchEditor : A.K. SinghOxford & IBH Publishing Co.,1991

XIIIAIRAPT—International Conference on High Pressure Science ami Trrlmnlagy. /W/ , p p 7 9 0 ~ 7 9 7

6. THEORY OF RESPONSE OF RUBY FLUORESCENCE TOEXTERNAL STRESSES

Surinder M Sharma' and Y.M. Gupta2

'High Pressure Physics Division, Bhabha Atomic Research centre. Bombay 400 085.India.'Shock Dynamics Laboratory, Department ot Physics, Washington State University.Pullman, WA-99164-2814, USA

A theoretical approach to analyse the shills ol ruby H-linas under dilferent typas ol

deformations: unlaxial compressh/e/tenslle strains, hydrostatic compression and unlaxlal

•tresses has been developed by us (12). An outline ol this theory is presented hare and a

brief summary of results obtained is given.

Key words: Ruby fluorescence

16

Rvecnt Tr«nda in High Fxr<M»ur« R«M«rchEditor : K.K. SinghOxford 6 IBB Publishing Co.,1991

pp 878-880

7. PRESSURE INDUCED ELASTIC ANOMALY IN Zn

Sminder M. Sharnta, S.K. Sikka and R. ChidambaramHigh Pressure Physics Division. Bhabha Atomic Research CentreBombay 400 085. India

X-r«y diffraction study of Zn has been carried out to V/Vo •.92 to investigate the effect of expected elastic stiffeningon c/a. After initial decrease c/a attains a constant valueof about 1.8. Present results arm at variance with the earlierdata of Lynch and Urlcksmer and In reasonable agreement withrecent total energy calculations.

Keywords Zinc. Elastic anomaly

XIIIAIRAPT— International Conference on High Pressure Science and TtckHoUnjy. 1991, pp 3 3 1 - 3 3 4

3. GROUP IV B ELEMENTS UNDER PRESSURE: ACOMPARISON BETWEEN THEORY AND EXPERIMENTS

JyothiS. Gyanchandani, S.K. Sikka and R. ChidambaramHigh Pressure Physics Division. Bliabha Atomic Research Centre. Bombay 400 065India

Ti, Zr and Hf under pressure show two transitional <x*i& and0)4-0 (o=hcp, o)-3 atom hexagonal and f£*bcci. a-Hd transitionoccurs at 2, 2, 36 GPa and ur*8 a t>87 , 30 and 71 GPa respec-t ive ly . These transitions are believed to be driven by s+delectron transfer. Here, we analyze the trends in these tran-sit ion pressures.

Keywords: Phase transitions, s*d electron transfer, Ti, Xr,Hf.

17

XIUAI*A>r—!mtnuiioHslCoi4tr**to*Hitkf,,uwtStinc*mdTtc*mU$t.im , pp 803-806

9. ON HIGH PRESSURE STANDARDS

B.K. GodwaP and Raymond Jeanloz''High Pressure Physic* Division, Bare, Bombay 400085. Imfa•Department of Geology and Geophsics. University of CaHomia,Berkeley. CaKtomia. CA 974720. USA

High Pressure standards performance i s evaluated using dynamicshock wave, s tat ic diamond anvil ce l l and laser heated diaaondanvil ce l l studies. Structural s tabi l i ty and consistencyof data for materials under different conditions qualifythem as high pressure standards.

Keywords: High pressure. Standard, DAC, EOS, Calibration

Recent Trends in High Pressure ResearchEditor : A.K. SinghOxford & IBB Publishing Co.,1991

XIIIAIRAPT—International Conference on High Pressure Science and lechmAnXy. 1991, p p 3 2 8 - 3 3 0

10. PRESSURE VARIATION OF THE (c/a) RATIO OF ZINC FROMTHE FIRST PRINCIPLES ELECTRON BAND THEORY

S. Meenakshi, V. Vijayakumar, B.K. Godwal and S.K. Sikka,High Pressure Physics Division, Bhabha Atomic Research Centre. Trombay,Bombay-400 085. India.

The results of first principles total energycalculations as a function of c/a under pressureusing linearized muffin-tin orbital method arepresented for the element Zn. The c/a value is foundto decrease smoothly upto v/vo • 0.925 and then showsa discontinuity and again decreases to the idealvalue. The c/a variation with compression differsfrom the earlier experimental data.

Keywords:total energy calculations, LMTO method, c/avariation,compression.

18

XUtAHtAPT— ImetnalkmalCtmfrrrmtnnMi** PnuurtSrirmramiInrl&'ti'ty. 1991 , p p 7 6 6 - 7 6 8

11. A MINIATURE CLAMP TYPE DIAMOND ANVIL CELL FORX-RAY AND OPTICAL MEASUREMENTS

V. Vijayakumar, S. Meenakshi, B.K. Godwal, S.K. Sikkaand R. ChidambaramHigh Pressure Physics Division. Bhabha Atomic Research Centre. Trombay,Bombay - 400 085. India.

Details of a mini diamond anvil cell which can alsoserve as a normal Mao-Bell type DAC is given togetherwith some results of preliminary Raman and X-raymeasurements carried out to'evaluate its performanceand the suitability of amorphous metal as gasket.

Keywords: mini diamond anvil cell, spectroscopicmeasurements, amorphous metal gasket.

Recent Trends in High Pressure ResearchEditor : A.K. SinghOxford & IBH Publishing Co.,1991

\W AIK APT—International Conference on High Pressure Science antTechnoiofy, 1991 , p p 2 4 2 - 2 4 4

12. RAMAN SCATTERING STUDY OF PHASE TRANSITIONS INRESORCINOL AT HIGH PRESSURE

S.K. Deb1, M.A. Rekha'. A.P. Roy', V. Vijaykurnai*.S. Meenakshi and B.K. GodwaF'Solid State Physics Division,'High Pressure Physics Division,Bhabha Atomic Research Centre, Bombay 400035, India

Apart from the <X - B transformation in resorcinol at 5 Kbarreported in the literature, a new phase baa been foundabove 40 Kbar. Here the external lattice modes virtuallydisappear in the Raman spectra while the internal modesof the molecule persist. On relieving the pressure the, recrystallization to the original phase is found to besluggish. Its implication with regard to amorphizationhas been discussed.

Keywords: Raman scattering, Resorcinol, amorphization.

19

Joint AIRAPT/APS Conference on High Pressure Science andTechnology, Colorado, USA (1993)

13. THEORETICAL ANALYSIS OF THE ISOSTRUCTURAL TRANSITION IN Zr AT 53 CP*

Jyoti H. Daswani .Satish C.rjupta S.K. Sikka and R ChidambaramHigh Pressure Physics DivisionBhabha Atonic Research Centre

Bombay 400 0B5. India.

Recent diamond anvil x-ray diffraction measurements in Zr show a first orderisostructural transition at 53 GPa. ( v/Vo « 0.68 ) .in addition to the knownhep to u and u to bcc transitions at 6.7 GPa and 33 GPa respectively. Thistransition has been attributed to the completion of s • d electron transfer inZr Here we have performed ab-initio band structure calculations to analysethis transition. Our two panel LMTO calculations (that also include the 4pcore states ) rule out the completion of s • d electron transfer upto V/Vo-0 55 Although the 4p ror» lovnlrs broaden t-o about 315 mRyd. these also donot cause any discontinuity in the calculated isotherm. This suggests thatfurther experimental work is needed to check the reported transition.

Joint AIRAPT/APS Conference on High Pressure Science andTechnology, Colorado, USA (1993)

14. ON 5f BAND OCCUPATION IN SHOCK COMPRESSED THORIUM

Satish C. Gupta, N. Suresh and S.K. SikkaHigh Pressure Physics DivisionBhabha Atomic Research CentreBombay 400 085. India.

The universal equation of state of Th based on the recent high pressure X-raydiffraction measurements displays a non-linear behaviour which is interpretedfrom band structure calculations as due to inter band spd-«f electron transfer.However, the available shock wave measurements (up to 137 GPa) show thelinear Vg- U relation. We have compared the two sets of data and observe

that, the 300 K isotherm reduced from the shock Hugoniot agrees very wellwith the static measurements. This implies that the 5f band also getsoccupied in Th under shock compressinn. This also suggests that the linearVg- V relation contains information about an electronic transition. This

has been further confirmed by analysis of static and shock data on Uranium.

20

Joint AIRAPT/APS Conference on High Pressure Science andTechnology, Colorado, USA (1993)

15* Molecular Dynamical Calculations of a- quartzImplications tor Shock. Results

M.S. Somayazulu, Surinder M Sharma ,S.K. SikkaMandini Garg and S.L. Chaplot*High Pressure Physics Division• Solid State Physics DivisionBhabha Atomic Research Centre

Bombay 400 085, India .

Ma have carried out detailed molecular dynamical calculations as a functionof pressure and temperature on Sio? with a-quartz as the initial phase. Atroom temperature, on increase of pressure beyond 21 GPa, we get anisotroplcamorphous phase. The glassy phase recovered on release of pressure continuesto be compacted and has an average Si-O coordination of about 4.6. The glassbecomes isotropic and four coordinated beyond lOOOK. The calculated equationof state suggests that tlie high pmnmire phase of or-quartz in shockexperiments is amorphous with higher coordination of Si and not stishovite.These calculations explain some of (-lie recent experimental results on theshocked recovered phase. ThR hph.-iviour <if pr«»sniir<? induced glass in alsocalulated and is compared wiLh t:lmi. >>i ••.-ilculnl-ml rnrinllrn of Funnd silica anrlexperiments.

Joint AIRAPT/APS Conference on High Pressure Science andTechnology, Colorado, USA (1993)

16. PHASE TRANSITION IN POTASSIUM TITANYL PHOSPHATE (KTP) UNDERHIGH PRESSURE

H. S. Somayazulu, Hema S Ramachandran, Surinder M Sharma,and S. K. Sikka

High Pressure Physics DivisionBhabha Atomic Research Centre

Bombay, 400 085, India

Raman scattering experiments on KTP (<S.A KotiroukliB et'al, 19871,indicate a phase transition to a lower symmetry phase around 6GPa. To investigate the. struct in:P ol this high pressure phase, vehave carried out an eiiRrqy-iHniinrni v» x-rny diffraction atudy ofthe powdered sample lining > n (Ij.-itiimttl nnvi) cell and fulldiffraction cones of 51 anr] 6 . 'I'IIP rJafa was analysed in terms ofthe recently determined structure of the high pressure phase ofKTP <Allen and Nelmes, 1992). H» Eincl that our experimental datais in full agreement and thetpii"i-** confirm that KTP undergoes aniso-spacegroup transit ion at about. 6 GPa.

21

Joint AIRAPT/APS Conference on High Pressure Science andTechnology, Colorado, USA (1993)

17. HIGH PRBSSURB RAMAN STUDIES ON p-DICHLOROBENZENB.

S.K. Deb1, S. Meenakshizand B.K. Godwal2

1 Solid State Physics Division,2 High Pressure Physics Division,Bhabha Atomic Research Centre,

Bombay 400 085, India.

He report the results of Raman measurements on p- dichlorobemeneup to the pressure range of 80 kbar much higher than the limit of 20kbar reached in the past. The ambient a phase remains stable up to 80kbar when the pressure is changed rapidly ( ~ every 2 hours ).However, at low pressure ( * 5 kbar) it transforms to » phase veryslowly (after * 16 hours) and continues to retain this phase tillabout 80 kbar. The Raman frpqii/>nry variation with-pressure does notshow any drastic clianqr» in vninr-or slope, indicative of any furtherphase change.

Joint AIRAPT/APS Conference on High Pressure Science andTechnology, Colorado, USA (1993)

18. ON THE PRIMITIVE HEXAGONAL AMD u PHASES OF CARBON

R.S.Rao, B.K.Godwal, and S.K.SikkaHigh Pressure Physics Division, Bhabha Atomic Research Centre,

Bombay - 400 085, India

Structural transitions in diamond at ultrahigh pressures are of great currentinterest. Theoretical estimates show that the first transition in diamondwould be to the bc-8 structure near 11 Mbar. However, the stability ofprimitive hexagonal (ph) structure of carbon has not been studied so Carthough Si and Ge, also group IVB elements , are known to transform to thisstructure under pressure. Hence we carried out the first principles linearmuffin-tin orbital (LMTO) method total energy calculations for the phstructure (with empty spheres) in comparision with other postulatedstructures, with the motivation to examine whether diamond would transform tothis, structure. We find that ph and the simple cubic structures are ofcomparable stability at megabar pressures, but ph becomes more stable near17 Mbar. Calculations are also reported for u structure of carbon, which alaooccurs in group IVA elements under pressure.

22

Joint AIRAPT/AFS Conference on High Pressure Science and Technology,Colorado, USA (1993)

19. STERIC CONSTRAINTS : A POWERFUL CRITERION TO PREDICT THE ONSETOF PHASE TRANSITIONS IN MOLECULAR SOLIDS UNDER PRESSURE

S.K.8ikka, Surinder M Slinrma and R. ChidambaramHigh Pressure Physics DivisionBhabha Atomic Research Centre

Bombay 400 065, India

Analysis of molecular crystals show Mint there are naturally occurringlimiting values for the non-bonded enutnet-s between various atoms. Thesesymbolize the dominance of repulsive forces at distances smaller thanthese limiting values. We show that these limiting distances can be usedto predict the onset of phase tmiisitions in these crystals under highpressure.

Joint AIRAPT/APS Conference on High Pressure Science and TechnoloevColorado, USA (1993) w"«yt

2Q. OH TETRAQOHJVL DISTORTION 1H INDIUM UNDER PRESSURE.

8. Meenakshi, B.K. Godwal, R.9. Rao and V. VijayakumarHigh Pressure Physics Division,Bhabha Atomic Research Centre,

Bombay 400 085, India.

Results o£ linear muffin-tin orbital calculations tor tetragonaldistortion under pressure in Indium are compared with the existingexperimental data. We find that c/a values as a function of volumeshow a broad maximum and then show a decrease in agreement with thedata. Within atomic sphere approximation we simulate theexperimentally observed structural phase transition. The possiblecaua« of turnover in the axial ratio Is also discussed.

23

Presented at SAINR-93, Proc. of tint ional Symposium on ArtvniuwlInstrumentation for Nuclear Reopni.crli (SAINR-93), pJ-1, Jan' 1991

21 . PC BASED M M DATA ACQUISITION. ANALYSIS ANO CONTROL SYSTEM

FOR ENERGY DISPERSIVE X-RAY UIITF.RACTION (EDXRD) EXPERIMENrs

AT mm M&

S. N. MOM1N AfJM R.SiVA BHASKARHIGH PRESSURE PHYSICS DIVISIONBHABHA ATOMIC RESEARCH CENTRE

This paper describes I lie development of hardware amisoftware for a PC based data Acquisition, Analysis and Controlsystem for Energy Dispersive X i ay Diffract:ion Experiments at highpressures. The user interact ion, control and data processing isdone by using a PC-XT/AT, W!PIO HP the actual data acquisition ipcarriedout in a microcomputer (SOBSA) based data acquisitionmodule (DAM; . Once the moduJe if? initiated and programmed by thePC, it indepedently acquires data in shand-alone mode releivingthe PC free for analysis of previously collected spectra.

An interactive operating software package 'MCDAS' inTurbo Pascal lanquage has boon developed and integrated forEDXRD/ADXRD data acquisition nyfst PHI. Thin package controlling DAMmodule is a versatile one with menu driven options for livedisplay of spectrum on the PC terminal, data handling andpreliminary processing. Some oC the hardware & software specialfeatures of the data acquisition system are as follows :

* The DAM is a microcomputer (8085A) controlled with 4K/8Kchannel memory, having counting capacity = 16 x 10 counts/channel

* Fast data accumulation is implemented by using direct memoryaccess (DMA) mode of 8085A microprocessor. The module accepts1 MHz input count rate.

* Stand alone operation of DAM permits to make PC free foron-line control of motors or further processing of previouslyaccumulated spectrum.

24

A(3). BARC REPORTS

BARC/1991/E/013

1. STUDY OF ALIGNMENT OF DIAMOND ANVIL CELL BA8BD SMBXGY

DISPERSIVE X-RAY DIFFRACTION SY8TBM

S.Meenakshi and Surinder M Sharma

High Pressure Physics Division

Bhabha Atomic Research Centre

Trombay,-Bombay-400 085

ABSTRACT

A perfectly aligned EDXRD system consisting of a collimator,

diamond anvil cell and conical slit is considered and the

inherent flexibility introduced by the geometric constraints in

parameters like Brago scattering angle and the spatial range of

observability of the diffraction pattern are deduced within the

framework of geometric ray analysis. The consequences of

misalignment of the conical slit and the DAC are presented.

25

BARC/1992/E/037

2. Operation Manual for EDXHDDA - a software packagefor Bragg peak analysis of Energy Dispersive powder

X-Ray Diffraction Data

by

Balhans Jayaswal", V . Vijayakumar,S . N . Momin and S . K . SikkaHigh Pressure Physics Division

•Computer Division

ABSTRACT

EDXRDDA is a software package for analysis of raw data forenergy dispersive x-ray diffraction from powder samples. Itresolves the spectra into individual peaks by a constrainednon-linear least squares method ( Hughes and Sexton, 1988).Theprofile function adopted ia the Gauaaian/Lorentzian product withthe mixing ratio refinable in the program. The program isimplemented on an IBM PC and is highly interactive with extensiveplotting facilities. This report is a user's guide for running theprogram. In the first step after inputting the spectra, the fullspectra is plotted on the screen. The user then chooses a portionof this for peak resolution. The initial guess for the peakintensity, peak position are input with the help of a cursor or amouse. Upto twenty peaks can be fitted at a time in an interval of500 channels. For overlapping peaks, various constraints can beapplied. Bragg peaks and flourescence peaks with different halfwidths can be handled simultaneously. The program on executionproduces a look up table which contains the refined values of thepeak position, half width, peak intensity, integrated intensity,and their error estimates of each peak. The goodness of fie isjudged by the a discrepancy factor between the observed andcalculated spectra as well as visually on the screen with the helpof <full and difference plots. Error estimates are also used forthis purpose. The program is very general and can also be used forcurve fitting of data from many other experiments.

26

Project Report for ILTP Project No.6.2, 1991

3. AH ENERGY DISPERSIVE X-RAY DIFFRACTION STATION AT VEPP-3SYNCHROTRON BEAM LINE FOR THE STRUCTURAL STUDIES AT HIGH PRESSURES

S.K.Sikka, S.N.Momin, V.ViJayakumar, IJ.P.Talachko* ami R. ChidambaramHigh Pressure Physics Division, BARC, Bombay and 'MNP. Novosibirsk. Russia.

As a part of the SRS beamline utilisation at VF.PP-4 in Novosibirsk. Russia, anEDXRD station for high pressure studies is installed and made operational at aVEPP-3 beamline.The EDXRD setup (Fip,.l) consists of the following subsystems,(a) Adjustable primary beam collimanu . (It) A Mao-Hell typo diamond anvil rollmounted on a x-y-z-8-0 positioning stap.n, (c) A conical sill assembly to collectdiffraction data over a preset Bragg angle and (d) A complete data acquisitionand control system (Fig.2) based on IHM-PC/AT-386 computer and its software. Allthese subsystems, except (a), were designed and fabricated at DARC and shippedto the site and installed. In add M u m computer programs developed al DARC foranalysis of acquired data were also implpiiipnted on PC/AT al. Novosibirsk.

PCHtonu |/wu

MCI

i r * * I 1 ,.... I. I •<••'•' - " » I i

Hi! T ' TI

l-COMUl Hit

Fig. I — Schematic diagram of * Mgh pruiufe I

ow rrntctxt?! M « « H

A test data on a standard reference sample RbCl was collected upt.o 40 Kbai(Fig.3). The phase transition (NaCI > CsCl structure) at * 8 Kbar was observedand characterized.The quality of data in terms of acquisition time, peak widthsand statistics was found to be superior to the data acquired earlier on arotating anode x-ray generator at Trnmbay (Fig.3b).

:si:s

nno

ma-

151 IS

{sl\, 1

•I

3- Rb:i in CsJ: 'ntjr i; •> ( t j» a cs-:; »>c»» « = «.o

iHin

750?

SOIS

Hi mLi

* 7 W 1 .£i :5

CKANNEIS

27

A(4). ONLY ABSTRACTS IN CONFERENCES

1. Raman Scattering Study of Phase Transitions in T1N0,M.S. Somayazulu, S.K. Deb and A.P. RoySolid State Physics (India), 34C, 377, (1991).

2. Total Energy Calculations for Rational Approxi-nants ofQuasicrystalline Structures - Is the Centre of Mackay'sIcosahedron Really Empty ?S.K. Sikka, S.M. Sharma and R. ChidambaramSolid State Physics (India), 34C, 214, (1991).

3. Phonon Spectrum in Resorcinol from Inelastic NeutrcnScatteringS.L. Chaplot and B.K. GodwalSolid State Physics (India), 34C, 77, (1991).

4. Phase Transformations under High Static and Shock PressuresSatish C. GuptaSolid State Physics (India), 34C, 2, (1991).

5. High Pressure Phase Transition in Intermetallic CompoundAulnnS. Meenakshi, V. Vijayakumar, B.K. Godwal, S.K. Sikka, A.Jayaraman and R. ChidambaramSolid State Physics (India), 34C, 387, (1991).

6. Application of Ruby R-Line Measurements Under Shock Loadingto Pressure Calibration in Diamond Anvil Cell (DAC)ExperimentsY.M. Gupta, X.A. Shen and S.M. SharmaA.P.S. Shock Meeting, Williamsburg, Virginia, USA (1991)

7. Molecular Dynamical Studies of the Variations in Co-ordination and SiO Separation in a - Quartz under PressureM.S. Somayazulu, Nandini Garg, S.M. Sharma and S.K. SikkaSolid State Physics (India), 35C, 390, (1991).

8. Phase Transformations Under High Static and Shock PressuresS.C. Gupta (Invited Talk) Solid State Physics Symposium, atBHU, India, 34 C, (1991)

9. Condensed Matter at High Pressures and Temperatures .B.K. Godwal (Invited Talk) Plasma 91, Sixth National Symposiumon Science and Technology of Plasmas, (Indore, 1991).

10. Primitive Hexagonal and Tetragonal Face Centred DiamondStructure Studies of Carbon at Megabar PressuresR.S. Rao, B.K. Godwal and S.K. SikkaSolid State Physics (India), 35C, 389, (1992).

28

11. 5f-Band Occupation and Structural Transition of Thorium atMegabar PressuresR.S. Rao, B.K. Godwal and S.K. Sikka (Invited Talk)International Workshop on Electronic Structure Calculationsand Properties of Materials, Department of Physics, Collegeof Engineering, Anna University, Madras, India (1992).

12. Raman Scattering Studies on p-Dichlorobenzene upto 80 KbarS.K. Deo, S. Meenakshi and B K. GodwalSolid State Physics (India), 35C, 374, (1992).

13. Tetragonal Distortion in Indium Under PressureS. Meenakshi, R.S. Rao, B.K. Godwal and V. VijayakumarSolid State Physics (India), 35C, 373, (1992).

14. Steric Hinderance and Pressure Induced AmorphizationS.K. Sikka and S.M. SharmaSolid State Physics (India), 35C, 360, (1992).

15. On Pressure Induced Phase Transitions in C 6 0 SolidS.K. SikkaSolid State Physics (India), 35C, 359, (1992.)

16. A Energy Dispersive X-ray Diffraction Station at VEPP-3Synchrotron Beam Line for the Structural Studies at HighPressuresS.K. Sikka, S.N. Momin, V. Vijayakutnar, B.P. Valachko andR. ChidambaramSolid State Physics (India), 35C, 86, (1992).

17. Role of 5f Electrons in Structural Transformation & Equationof State of Thorium at Megabar PressuresR.S. Rao, B.K. Godwal and S.K. SikkaSolid State Physics (India), 35C, 79, (1992).

29

A(5). BOOKS/JOURNALS EDITED

Condensed MatterUnder Shock

PressuresProceedings of the

International Satellite Conferenceof XIII AIR APT,

Bombay. India,14th-15th October 1991

Edited by

R. Chidambaram. S. K. Sikkaand B. K. Godwal

GORDON AND BREACHSCIENCE PUBLISHERS

30

B(l). PAPERS IN JOURNALS

Physics of the Earth and Planetary Interiors. 73 0992) 264-273 26«Eltevier Science Publiihen B.V.. Amuerdun

1. Detection of weak seismic signals using stationarity of noiseand coherency of signals at a seismic array

Falguni Roy, S.K. Arora and T.K. BamSeismology Section, HPPD. Bhabha Atomic Research Centre. Bombay — 400 085. India

(Received 2 January 1992; revision accepted 11 March 1992)

ABSTRACT

Roy, F., Aioia, S.K. and Basu, T.K., 1992. Delecliun of weak seismic signals using stationarity of noise and coherency ofsignals at a seismic anay. Phys. Earth Planet. Inter.. 73: 264-273.

A basic problem in seismic cto'd analysis is the recognition of weak signals in the presence of ambient noise. Altboofb thecommonly used array processing method, which involves beam formation from the array data, provides a reasonableenhancement of the signal to noise ratio (SNR), it does not exploit the properties pertaining to stationarity of thebackground seismic noise. Prediction error fillers, on the other hand, because of their ability to accentuate smallnon-stationary changes, can be effectively employed to detect weak signals in a stationary noise background. In this paper, itis shown how these two signal detection methods can be used in cascade to achieve an overall high SNR. Through theanalysis of some artificial and real seismograms it is demonstrated that an average SNR improvement of up to a factor of tenis possible by the combined method of signal Selection, using data from the Gauribidanur array.

CURRENT SCIENCE, VOL. 62. NOS. 1 & 2, 25 JANUARY 1992 p p 1 9 9 - 2 1 2

2. DEVELOPMENT AND DEPLOYMENT OFRADIO TELEMETERED SEISMIC NETWORK

AT BHATSA

V. C. KOLVANKAR, V. N. NADRE, S. K. ARORA AND D. S. R A O

Seismology Section. Bhabha Atomic Research Centre. Trombay, Bombay 400 085

ABSTRACT - An indigenously built, eleven station radio (wireless) telemetered seismic network (WITSENjwas commissioned at Bhatsanagar. Shahapur Taluka. Thane District. Maharashtra State, early in 1988 tostudy the reservoir induced seismicity (RIS) of the region. This paper discusses the development oj thisnetwork in general and in particular the technical details of carious laboratory and field equipments developedand deployed. Various illustrations of signals from local micro-seismic events, events occurring in about fewhundred kilometers and teleseismic events acquired by the network are provided. Comparison is made withdifferent types of systems for acquiring micro-earthquake data which were adopted by different localinstitutions in the past. Future research and development efforts required to improve the capabilities of suchnetwork are also discussed.

31

199

VoL 10. No. 2. W/,pp 39 -52

3. Elastic Wave Propagation with Kinematic DiscontinuityAlong a Non-Ideal Interface Between Two Isotropic ElasticHalf-Spaces

Gurajada Suryanarayana Murty1 and Vijai Kumar*

The problem of wave propagation along the interface between two elastic, isotropic, tad homo-geneous half-spaces is studied when the half-spaces are coupled through a vanishingly thin layerof Voigt material. It is assumed that the separation, 2// , between the half-spaces, and the complexrigidity-modulus, t*. of the layer are both vanishingly small, bui 'jic complex quantity >i/2ff remainsCute.

la a series of experiments to which two blocks of elastic materials with or without lubricant/couplant at the interface are subjected to an external load normal to the interface, the variation ofthe speed and attenuation of interfacial waves, generated and detected by piezoelectric transducers,was measured as a function of external load. Assuming a nonlinear relation between external loadu d tt/ZH, the experimcBtal data is interpreted theoretically, and the best-fit parameters of thenonlinear relation arc determined.

For the 13 cases of interfaces studied, with or without lubricant/couplant, satisfactory agree-ment was found between experiment and theory, except in one case. Even in this case, theagreement is satisfactory in the lower range of load. It is hoped that this study will be useful indeveloping nondestructive methods of testing the bonding conditions at an ioterface between elasticmaterials by means of intcrfaciai wave properties.

KEY WOKDS: Elastic wave pjopagaiioo; ooodextruciive evaluation; ultrasonics; bonded material inspection;adhesive bonds; iaterfacci.

JOURNAL GEOLOGICAL SOCIETY OF INDIAVol. 39, Feb. 1992, pp. 162 to 167

4. Mechanism Solution of Burma-India BorderEarthquake of August 6, 1988

A. R. BANGHARSeismology Section, Bhabha Atomic Research Centre, Trombay, Bombay

Abstract. This paper presents the focal mechanism solution for the Burma-India borderearthquake of August 6, 1988, Use was made of the first motions of P waves andpolarization (or first motions.) of S waves. The mechanism solution is characterised bya predominant component of thrust faulting. The deduced orientation of the axis ofcompression is northeasterly. This orientation of the axis of compression is nearlyparallel to the trend of tectonic features in the cpicentral region of this event.

Keywords: Earthquake, Mechanism Solution. India, Burma.

Bull. Ind. Soc. Earth. Tech., Paper No. 308. VoJ.28, No.3. Sept. 1991, pp. | ,„ | 2

PLANNMG MICROEARTHQUAKE INVESTIGATIONS M REGIONS OF NUCLEARPOWER PLANT SITES

By

S.K. AroraSeismology Section

Bhabha Atomic Research Centre, Bombay

ABSTRACT

In a selected region where in important structure such as nuclearpower plant, high dam or a large industrial complex is planned, itis necessary to carry out systematic seismic investigations startingwell before the construction phase and extending preferably over thewhole operating life time of the plant. This paper highlights theimportance of such investigations that are related to seismicity andseismotechtonic status of the region through acquisition of data ofmicrosarthquakes constituted by very small seismic signals of relativelylow magnitude but high frequency of occurrence. The procedure forestablishing small aperture telemetered microearthquake networkinterfaced to a centralized digital recording and data processingfacility is described. A scheme is presented wherein the data generatedby continuous regional seismic monitoring are analysed using estimatesof source location, signal duration magnitude, b-value profile, powerspectra, spatiotemporal changes in seismicity, local crustal structureand other pertinent parameters for seismotectonic assessment ofthe region.

Bull. Ind. Soc. Earth. Tedi.,Paper No.314,Vol.29,No.l,March,l992,pp.l7-33

SEISMIC N O B ^ E ^ U R ^ E N T ^ T H ^ R I G ^ AROUND

By

S.K. Arora, M.K. Bhat, A.G. Kulkarm, T.K. Basu and K.R. SubbaramuSeismology Section

Bhabha Atomic Research Centre, Bombay

ABSTRACT

Measurement of background seismic noise in three provinces around

1 5 £ SZ»Xh&& Xb.eTystem incorporating a wide band cassette magnetic tape recorderand a band Jimited helical chart recorder. Several noise samples obtainedduring May 23-25, 1989 and spectral analysis of these data show thatthe high frequency noise that interferes in signal detection is practicallyabsent in Kulgi area, moderate at Idagundi and comparatively largest inKumbarwad province. Although the relatively long period oceanic micro-seismics have comparable energy in all the three provinces, Kulgi air.ongthem is found to be overall quietest locality which qualifies to rave asensitive microearthquake monitoring statif"

33

JOURNAL GEOLOGICAL SOCIETY or INDIAVol. 37. Jan. 1991, pp. 25 to 30

Mechanism Solution of Nepal-Bihar Earthquake ofAugust 20, 1988

A. R. BANGHARSeismology Section, Bhabha Atomic Research Centre, Tron-.bay. Bombay (India)

Abstract. This paper presents the focal mechanism solution of the Nepal-Bibarearthquake of August 20, 1988. Use was made of the first motions of P wave* andpolarization (or first motions) of S waves. The mechanism solution is characterized Itfa predominant component of strike-slip faulting. The deduced orientation of the axilof compression is nearly north-south. This orientation of the axis of compression is inagreement with the axis of compression deduced from the mechanism studies forHimalayan earthquakes.

Keywords; Geophysics, Seismology, Nepal. Bihar, earthquake.

Bull .Ind.Soc.Earth.Tech., Paper No.328. Vol.30, No.1, Mar.1993, pp.1-17

MEASUREMENT AND INTERPRETATION OF VIBRATION RESPONSEOF A CONCRETE PEDESTAL CAST OVER BEDROCK

Y.S. Bhadauna, S.K. Arora and Vijai KumarSeismology Section

Bhabha Atomic Research CentreTrombay, BOMBAY - *00 085

ABSTRACT

In this paper we present vibratory characteristics of a typical concretepedestal cast over bedrock in a ground floor room of a large laboratorybuilding at our Centre, to mount a sensitive spectrometer on it. Aroundthis pedestal is provided a rectangular channel of small width filled withdry sand as vibration damper. In a seismic experiment, the vibrationisolation response (transmissibility) oi this pedestal has been measuredand interpreted. The transmissibility has been computed from powerspectra of .artificially generated transient signals produced at the timeof the experiment by dropping a small weight on the floor and detectedsimultaneously by seismic sensors installed at the base as well as atthe top of the pedestal. Essentially, the coherence between such pairsof signals has been used to interpret the transmissibility peaks. Fromthe wide band accelerographic data, the pedestal is found to have apprecia-ble transmissibility in the frequency band 9(K1!O Hz peaking at 102 Hz.

34

B(2). PAPERS IN CONFERENCE PROCEEDINGS

Proc. Sth conference on acoustic emmission/microseismic activityin geologic structures and materials, The PennsylvaniaUniversity, June 11-13, 1991. (In press)

1. PC-388 based subsurface rockburst aonitoring systea for Kolar

gold mines

G.J.Nairi, N.M.Rajua and J.D.Gupta*

1 Seismology Section, Bhabha Atomic Research Centre, Bombay.2 National Institute of Rock Mechanics, Kolar.3 Computer Division, Bhabha Atomic Research Centre, Bombay.

Abstract

The deep gold mines of Kolar in India are incessantly rocked bydamaging rockbursts especially when the mining activity runs intoMysore North Fault traversing the reef. The rockburst on 26September, 1990 was one among these damaging rockbursts occuringclose to reef and fault and it caused fissures in the main shaft.In order to increrase the safety of the miners against such fatalrockbursts, a compact PC-386 based system was developed and in-terfaced to a 10 geophone network in Northern Fold region ofKolar Gold Fields, India. The on line rockburst monitoring sytemcode named SRBM (Subsurface Rock Burst Monitoring system) is ins-taled at a depth of 2 km below surface and is connected via modemto the surface laboratory at 4 km distance. The system can detectevents coming at a peak avalanche rate of 30 events per minuteand transmit the source parameters to the surface laboratory. Thepaper presents some details of the precursory microseismic ac-tivity of the 26 September 1990 event and a brief description ofthe subsurface rockburst monitoring system installed at KolarGold Fields.

Proc. 5th conference on acoustic emmission/microseismic activityin geologic structures and materials, The PennsylvaniaUniversity, June 11-13, 1991. (In press)

2. Microseisaic precursor analysis prior to seismic events in KolarGold Fields - a case study

C.Srinivasan, N.M.Raju and G.J.Nair*

National Institute of Rock Mechanics, Kolar• Seismology Section, Bhabha Atomic Research Centre, Bombay.

Abstract

The • paper discussed the behaviour of microseismic sourceparameters with time. These parameters are obtained from PDP 11/3based real time system and are characteristic of the rockburstprecursors of Champion Reef Mine, in Kolar Gold Fields,Karnataka, India. The pattern of microseismic events recordedprior to rockburst indicate that in majority of the cases themain event is preceeded by substantial increase of microseismicevent rate followed by a sudden decrease in the event rate. Thepaper also discusses the behaviour of microseismic activity pat-tern prior to major rockbursts. The spatial distribution ofevents prior to rockbursts, clustered around the region of even-,tual failure.

35

froo* 15th ASI Meeting, Astronomical Society of India,Bombay, 2-5 March,1993.(In press).

5. SERVO TO REPLACE CONCRETE PIERS

B.N. Karkeral and S.K. Arora2

Bhabha Atomic Research CentreI. Technical Physics and Prototype Engg Division

2. Seismology Section

The scheme discussed here is intended to replaceconventional concrete piers for mounting highprecision measuring instrument such as advancedoptical telescopes. It is based on the experiencegained during the commissioning of the controlsystem of 2.34 M Vainu Bappu Telescope (VBT) atKavalur by Reactor Control Division of BARC. Inaddition, the scheme incorporates active isolationtechniques used to support precision optical benches.Photograph of a passing star cluster taken throughVBT by switching off the servo system and henceengaging the brakes in the counter torque modeshowed oscillating star tracks with frequency

. matching the natural frequency of the telescopestructure with amplitudes around 10 arc seconds. Thepossible sources of noise in this oscillation are the

concrete pier and pressure fluctations in thehydrostatic bearings. To overcome this and few otherrelated problems, the sensitivity of the control systemis increased by amplifying the (echogeneraior feedback by a factor of about 250. With this, photographof the same passing star cluster, taken after a gap offew minutes of the above photograph, with instructionto the servo system to maintain zero speed, showedsteady star tracks without any noticeable oscillation;hence less than 0.1 arc sec It is possible to extend thecapability of the servo system by bringing into its foldthe secondary mirror anJ also a third mirror, ifrequired. The approximate values of naturalfrequencies to be handled are listed below-

36

Primary Secondary ThirdMinor Mirror Mirror

Telescopes (full structure)

VBT class 3 Hz 30 Hz 300Hz4 M class IHz 10 Hz lOOHz8 M class 0.3 Hz 3 Hz 50HzThe three tier servo sxstem, controlling primary (fullstructure), secondary and third mirrors should providenoise isolation, similar to VBT experience of thefollowing ranges. The noise isolation aimed at is lessthan the smallest value delectable by any focal planeinstrument.

Telescope

VBT classA M classS M class

MlServo

1 Hz0.3 Hz0.1 Hz

M2Servo

10 Hz3 Hz1 Hz

M3Servo

100 Hz30 Hz15 Hz

Wilh ihis, it should be possible to dispense withconventional concrete piers for ground noise isolation.To supplement the servo capabilities at higherfrequencies of vibration and to provide redundancyinitially, in the first few telescope installationswithout piers, it is recommended to adopt activeisolation techniques commonly used to supportprecision optical apparatuses. For achieving vibration-free mounts capable of carrying large pay loads, it issuggested that a mount supported on multitier aircushion would be a robust arrangement among activemethods of base isolation meeting all therequirements. The trunsmissivity of such a system canbe estimated by spectral analysis of seismic data ofartificially induced seismic disturbances such astransients, in a wide frequency band ranging from fewHz to few lens of Hz.

37

4. Elaborate seismic noise measurementsin and around Kaiga region

SJCArora. M.K.Bfui. KKSUUMMML, T X B M U and A.G.KulkamiHhabJu Aiam* Himmk Cmm, Bombay,

ABSTRACT

In (he KX-OTH) and an elaborate tcuouc iwuc MU%C> cipamtM ftindurmd atound Kaiga region in Kamaiaka, toulhemlalta, during December, 1989, new alternative lu* m>o* uica ha»« teen ciplofcd in ihc two province! of Idagundi andKianbar *ul. M two tile* in ihc»t province*. tuckcruuoJ autmic not** ha* been measured uung aa tndifanouiJy deveiopedpcvubU fulj mcuidin( tyiuun Uui aujuuc* anjJug; d*u on cauenc majneue upe» at well at on paper chant. The machinetlmilurd U(>c tcctxJs have been »pecn«l wuiyioi uid die ictulu caUauad wuh (he dala obtained fron paper recanli. Hie studyUk>wi Uui Uic uccwuc nucroteunu of newly I w jitikxJ hjve comparable energy at bach the tiiet at Kunbarwad and Idagundiand thai U».J>C »IU;> we piacucally free truni jcljinc lu^h fra|uency notset. The taller condiuon would permii installation oftciuuiic ktaiu'iit [iH muiutotm^ nucrocarthquake *>.iiv>i> in (he icjjsca

K»:)\*urdv Seismic noue; Ktu^a regwn. indigenous motuiortng sysietn. spectral analysis.

Proc.Syap.on Signal Processing and Modelling of Geosignaturea forexploration of Oil and Natural Gas, Varanasi, Feb.27-29,1992.

5> DBTECTION OF WEAK SEISMIC SIGNALS OSIMG PABAMSTRIC MODKLIHGOF SEISMIC ARRAY DATA

Falguni Roy, S.K. Arora and T.K.Basu,Seismology Section, HPPD.

Bhabha Atomic Research Centre, Bombay - 400 085.

ABSTRACT

In seismic data analysis, it is important to detect and

recognise weak signals that are often masked by ambient noise.

The commonly used method of beam forming of seismic array data is

Able to provide reasonable improvement in signal to noise ratio

(SNR), but it does not exploit the properties pertaining to the

stationarity of the background noise. Parametric models of time

series. such as autoregressive models, due to their ability to

predict a stationary time series one or more steps ahead with

reasonable degree of accuracy, can be effectively employed to

distinguish small non-stationary changes due to the presence of

weak seismic signals in a stationary noise background. Thus,

these two relatively independent signal enhancement methods can

be used in cascade to substantially increase the overall SNR.

This has been demonstrated by processing some artificial

seismograms as well aa che data of somo real seismic events

obtained from Gauribidanur array.

B(3). BARC REPORTS

6.A.R.C./I-1018

1. A REPORT ON THE GLOBAL SEISMIC DATA

EXCHANGE EXPERIMENT

by

Vijtl Kumar and R.N. BharthurSeismology Section

BHABHA ATOMIC RESEARCH CENTREBOMBAY, INDIA

1991

Abstract i A global seismic data exchange experiment M M carriedout during January-March 1990. In this experiment a number ofcountries including India contributed seismic data of theirseismic stations to the experimental international seismic datacentres. In this report, the details of data preparation,national and international computer to computer communicationlinks used for data transmission, volume and quality of data,expenditure involved and problems encountered arm described.

BARC/1991/I/017

TABLES OF APPARENT PHASE VELOCITIES AND TIME DELAYS FOR

ARRAY PROCESSING OF DIRECT P AND S SIGNALS AND

OF PKP AND PP SIGNALS IN THE CORE SHADOW

REGION AND BEYOND

by

T.K. Basu, S.K. Arora and F. RoyHigh Pressure Physics Division

BHABHA ATOMIC RESEARCH CENTREBOM3AY, INDIA

1991

Abstract i A recent surge of Interest to process mrrmyseismograms in the core shadow region and still farther awayfrom the sources is motivated by the usefulness of PP and PKIKPsignals in further development of efficient signal detectors andidentifiers. The present tables provide expected apparent phasevelocities and time delays of these two important signals atGauribidanur seismic array in the distance range 110 A^TIBBand In 5 steps of azimuth for full range 0 ^ Z <360 , inaddition to the same parameters for P, S and PP signals up toA - 105° limited by direct arrivals. Although the tables assumeprimarily surface focus source, they incorporate, based on ascheme suggested in this paper, necesnary corrections for actualfocus depth corresponding to an agumented value of theepicentral distance.

39

B.A.R.C. - 1548

3. RELATIVE ABUNDANCE OP PcP ENERGY IN EXPLOSION

SEISMIC SIGNALS PROM EASTERN KAZAKH AND SOUTHWESTERN

RUSSIA RECORDED AT ESKDALBMIIR, ULLOWKNIFB AND GAURIDIDAWR ARRAYS

byT.K. Basu and S.K. Arora

Seismology SectionBHABHA ATOMIC RESEARCH CENTRE

BOMBAY, INDIA

1991

Abstract : In this study we gather further evidence of relativeabundance of PcP (core reflected P> energy in explosion seismicrecords. It is based an the analysis of temporal and spectralcharacteristics of P and PcP digital seismograms of twenty-threeunderground nuclear explosions in Eastern Kazakh and SouthwesternRussia recorded at Eskdalemuir (EKA) and Yellowknife (YKA) arrays.The results are compared with those obtained earlier usingGauribidanur array (GBA) data. It is -found that seismic sources inSouthwestern Russia give consistently large values of the PcPidentifier when both EKA and YKA data are used thus corroborating ourearlier finding with regard to this Soviet region of typicalQ-strusture inferred from GBA data. As regards relative levels of PcPenergy in at least explosion generated seismic waves, it is found tobe substantially large at GBA, moderate at YKA and least at EKA.

B.A.R.C. - 1549

COMPRESSION AND DECOMPRESSION OF DIGITAL SEISMIC

WAVEFORM DATA FOR STORAGE AND COMMUNICATION

byY.S. Bhadauria and Vijai Kumar

Seismology Section

BHABHA ATOMIC RESEARCH CENTREBOMBAY, INDIA

1991

Abstract i Two different classes of data compression schemes.namely physical data compression schemes and logical datacomprassion schemes are examined for their use in storage andcommunication of digital seismic waveform data. In physical datacompression schemes* the physical size of the waveform is reduced.One, therefore, gets only a broad picture of the original waveform,when the data ara retrieved and the waveform is reconstituted.Correlation between original and decompressed waveforms variesInversely with the data compression ratio. In the logical datacompression schemes, the data arm stored in a logically encoded form.Storage of unnecessary characters like blank spaces is avoided. Ondecompression original data are retrieved and compression error %mnil. Three algorithms of logical data compression schemes have beendeveloped and studied. These are • 1) optimum formatting schemes, 2>differential bit reduction scheme, and 3> six bit compression ache**.Results of the above three algorithms of logical compression class mrmcompared with those of physical compression schemes reported inliterature. It is found that for all types of data, six bitcompression scheme gives the highest value of data compression ratio.

B ARC/1992/E/02*

5 . SEISMICITY OF PENINSULAR INDIA USING

GAURIBIDANUR ARRAY DATA FOR THE

PERIOD 1989 - 1991

by

B.K. Gangrade, S.K. Arora, A.G.V. Prasad and E. UnnikrishnanHigh Pressure Physics Division

BHABHA ATOMIC RESEARCH CENTREBOMBAY, INDIA

1992

Abstract I Seismic d#ta obtained at 6auribidanur array over • periodof three years from 1989 to 1991 and in the distance range less than10BB km from the *rr*y centre arc considered in 1000 local eventdetections during the 3-year period, a total of 2S2 presumed naturalearthquakes actually form the basis of this study. Eplcentrallocations *ra computed using the observed P to S time Interval andthe array determined azimuth. Earthquake magnitudes <M<* I computedessentially from duration of seismograms employing a formulationdeveloped earlier distribute the earthquakes in the range B.9 £ Itl4.9, though a large majority of them lay In the range 1.2 <£ ltC£ 2.6.All these events have been plotted on a geotectonic map of southernIndia. As expected for a shield province such as the Precambrianshield of southern India, the study shows that there are no suddenspurts of seismic activity and that large magnitude earthquakes arealso absent. A least-squares linear regression analysis has given theestimate of b-value at 0.673 that characterises the region.

BARC/1993/I/006

SEISMIC NOISE MEASUREMENT IN THE VICINITY OF CMTI.BANGALORE

BY

V.S.KamathSeismology Section, HPPD

BHABHA ATOMIC RESEARCH CENTREBOMBAY,INDIA

1993

Abstract: A seismic study conducted jointly by BARC and CentralMachine Tools Institute (CMTI), Bangalore is presented here. Anexperiment was conducted for determining normal (background) andmaximum ground vibration levels due to industrial and culturalactivity at the CMTI producing these vibrations. The sitesselected for seismic observations are those proposed for con-struction of a Precision Engineering Centre Building in the CMTIpremises. This paper also describes, in brief, plans to upgradethe measurement technique at CMTI for producing better qualitymeasurement data on machines. The measurement data is comparedwith simultaneous seismic noise to evaluate for the validity ofthe measurement taken. The results of the analysis of S O Mrecords are also presented in the report.

• 1

BARC/1993/1/013

7. RETRIEVAL OF DIGITAL SEISMIC DATA ACQUIRED BY A PC BASKDEVENT DETECTION SYSTEM AT DELHI SEISMIC UNIT

by

T.K.Baau, Falguni Roy, B.K.Gupta and S.K.AroraSeismology Section, High Pressure Physics Division

BHABHA ATOMIC RESEARCH CENTREBOMBAY, INDIA

1993

Abstract: A triangular seismic network has been operating atDelhi for last several years. Analog signals from three reist/tefield seismic stations of the network are radio transmitted to acentral recording laboratory (CRL) located at R.K. Puram, NewDelhi. At CRL the seismic signals are also recorded on a stripchart recorder. Recently, the network has been augmented with amicroprocessor based event detection and data acquisition systememploying a PC/XT to obtain digital data for further processingand investigations. The present paper gives details of theFORTRAN based software developed to retrieve the digital seismicdata recorded at Delhi in binary files which are stored in floppydiskettes and. archieved on cartridge tapes. The software alsosupports to plot multichannel waveforms along with time channelon a PC monitor or on a plotter. A few illustrations of thedecoded waveforms of real seismic events are included.

BARC/1993/I/014

8. DIGITAL MODEM FOR TELEMETRY OF SEISMIC SIGNALSUSING MILLER CODE

by

V.G.Kolvankar and V.N.NadreSeismology Section, High Pressure Physics Division

BHABHA ATOMIC RESEARCH CENTREBOMBAY, INDIA

1993

Abstract: This report discusses the development of a digitalmodem for telemetry of seismic signals using Miller code.Requirement of this type of modem for telemetry of seismic datawith wide dynamic range, selection of Miller code and selectionof ADC and DAC chips are discussed in detail. The added featuressuch as field programmable sampling rate, and number of inputchannels are highlighted.

42

B(4). PAPERS PUBLISHED IN HINDI

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47

SCIENTIFFIC AND R&D STAFF

STAFF

High Pressure Physics Division

Physics Group

Director Physics Group: Dr. S.S:Kapoor

Head HPPD: Dr. S.K.Sikka

A. Hioh Pressure Section

Dr. R.Chidambaram

Dr. S.K.Sikka

Dr. B.K.Godwal

Dr. S.C.Gupta

Dr. S.M.Sharma

Dr. M.S.Somayazulu

Shri S.N.Momin

Dr. V.Vi j ayakumar

Dr. R.S.Rao

Mrs. J.S.Daswani

Kutn. R. S . Meenakshi

Mrs. Nandni Garg

Shri K.D.Joshi

Shri Shiva Bhaskar

Shri N.Suresh

Total: 15

Administrative Staff 1

Technical Staff (Tradesman G downward) 0

Auxiliary Staff 1

Total staff: 17

B. Seismology Section

Bombay

Dr. S.K.Aroraa

Dr. A.R.Banghar

Dr. G.J.Nair

Dr. Vijai Kumar

Dr. Falguni Roy

Shri V.G.Kolvankar

Shri B.K.Gangrade

Shri T.K.Basu

Shri V.N.Nadre

Shri Y.S.Bhadauria

Shri A.Vijayakumar

Shri A.K Agrawal

Gauribidanur New Delhi

Shri R.N.Bharthur*3 Shri T.V.Sridharanb

Shri M.K.Bhat

Dr. H.Ramachandran

Shri D.S.Rao

Shri V.S.Kamath

Shri A.G.V.Prasad

Shri A.G.Kulkarni

Shri Uma Shankar

Shri Manoj Kumar

Shri E.Unnikrishnan

Shri B.K.Gupta

Shri P.C.Mitra

Shri D.Tewani

Shri MahendraSingh

Shri M.M.Kaul

Total: 12 10

Administrative: 1

Technical:* 2

Auxiliary:+ 1

Administrative: 1 Administrative: 0

Technical:* 9 Technical:* 2

Auxiliary: 5 Auxiliary: 3

Total staff: 16 25 11

a Head, Seismology Section

b Officer-in-charge

* Tradesman (G) and below.

+ Drivers and Watchmen

Published by : M. R. Balakrishnan,Head, Library & Information Services Division,Bhabha Atomic Research Centre, Bombay 400 085