ARTICLE IN PRESS

Applied Radiation and Isotopes 68 (2010) 1104–1107

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Applied Radiation and Isotopes

0969-80

doi:10.1

� Corr

E-m

journal homepage: www.elsevier.com/locate/apradiso

Review

Dose mapping using MCNP code and experiment for SVST-Co-60/B irradiatorin Vietnam

Tran Van Hung �, Tran Khac An

Research and Development Center for Radiation Technology (VINAGAMMA), 202A, Street 11, Linh Xuan Ward, Thu Duc District, HoChiMinh City, Vietnam

a r t i c l e i n f o

Article history:

Received 18 October 2009

Received in revised form

5 January 2010

Accepted 6 January 2010

Keywords:

SVST-Co-60/B irradiator

Absorbed dose

Dose Uniformity Ratio

Average dose

43/$ - see front matter & 2010 Elsevier Ltd. A

016/j.apradiso.2010.01.023

esponding author. Tel.:+84 08 62829158; fax

ail address: tranhungkeiko@yahoo.com (T. Va

a b s t r a c t

By using MCNP code and ethanol–chlorobenzene (ECB) dosimeters the simulations and measurements

of absorbed dose distribution in a tote-box of the Cobalt-60 irradiator, SVST-Co60/B at VINAGAMMA

have been done. Based on the results Dose Uniformity Ratios (DUR), positions and values of minimum

and maximum dose extremes in a tote-box, and efficiency of the irradiator for the different dummy

densities have been gained. There is a good agreement between simulation and experimental results in

comparison and they have valuable meanings for operation of the irradiator.

& 2010 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1104

2. Method and facility description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1104

3. Results and discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105

4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1107

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1107

1. Introduction

Gamma radiation processing has been growing around theworld. At present, there are more than 200 facilities used forsterilization of medical devices, food processing and otherapplications. In order to properly and effectively control andoperate the information on positions and values of maximum andminimum dose extremes, DUR and an efficiency of the irradiatorat interesting densities of product are very important. For thesepurposes dose mapping works must be done for selected densitiesfor a certain irradiator. The dose mapping can be performed byexperimental and simulation methods (Raisali et al., 1990;Pina-Villalpando and Sloan 1995, 1998; Oliveira et al., 2000;Sohrabpour et al., 2002). For the irradiator at VINAGAMMA dosemapping has been done for products with the densities 0.1, 0.2,0.3 and 0.4 g/cm3 by experiment using rice husk and sawdust as

ll rights reserved.

:+84 08 38975921.

n Hung).

dummies and ethanol–chlrorobenzene (ECB) dosimeter and bycalculation using the MCNP code.

This work presents results from dose mapping in productswith different product densities irradiated in SVST-Co-60/Birradiator at VINAGAMMA, Vietnam, by using MCNP code Version4C (Briesmeister, 2000) and experiment.

2. Method and facility description

Nowadays, MCNP code has been popularly used for calcula-tions in transport modes of neutron, photon, electron and theircombination. It is a good choice to use this code for calculation ofabsorbed doses in product at cobalt-60 and electron beamfacilities. MCNP code Version 4C has been applied to get dosemapping inside a tote-box at VINAGAMMA. For making input datafor the code detail descriptions of product transport system,source frames, a tote-box, shielding walls, source racks andmaterials used as dummy have been performed. The configurationin the calculation was modeled in accordance with real one of

ARTICLE IN PRESS

T. Van Hung, T. Khac An / Applied Radiation and Isotopes 68 (2010) 1104–1107 1105

facility, especially, in the irradiation room. Based on the practicaloperation of the irradiator, the irradiated material was simulatedwith four density values 0.1, 0.2, 0.3, 0.4 and 0.5 g/cm3. Incalculation of the dose distribution in product filled in tote-box,the calculation points were average absorbed dose in cubical cellsof 4 cm mesh size. The tally F6 mode has been used for dosecalculations. The accumulated dose at a position in a tote-box oraverage absorbed dose in a tote-box is the sum of 68 positions ofthe irradiated tote-box.

For experimental method, ECB dosimetry system was used formeasurements absorbed dose. The experiments have been donefor the dummy densities of 0.1, 0.2, 0.3 and 0.4 g/cm3. ECBdosimeters were located inside cartons filled with dummieshaving.

The irradiator SVST-Co60/B is a tote-box and wet storage type(the supplier is Isotopes Institute, Hungary). It is used mainly forsterilization of medical products, but also for food processing aswell due to its strong and durable product transport system. Theirradiator is product–source overlapping configuration type. Theproduct transport system in the irradiation room is constructed ofstructural steel. It surrounds the source racks lifted to theirradiation position. The system consists of four rows (passes),two rows are on both sides of the sources on two levels. The tote-boxes with the dimensions of 50 cm long�50 cm wide�90 cmhigh are moved on pass rails along the rows on two levels. Theboxes are moved side by side in each row rolling on their ownwheels. Eight boxes are set in each row, further 4 boxes are set inelevators and cross-transfer mechanisms at the ends of the rows.Altogether 68 tote-boxes are moved position by position in the

Upper level

Lower level

Source racks

Fig. 1. Schematic diagram of the product transport system.

Upper level

Lower level

Source racks

Fig. 2. The moving mechanism of the product transport system.

irradiation room at the same time. The movements of tote-boxeson rows are operated by pneumatic cylinders. Each tote-box iscarried into the irradiation room by a special car (tote-box car)and travels through 68 positions in the irradiation room as thefollowing manner: first, a tote-box is lifted up and passes fourparallel rows in the upper level then lowered and again passingfour parallel rows in the lower level. After irradiation finish with68 steps, the tote-box is carried out in the irradiation room bytote-box car. The irradiator has three source racks with fourmodules for each. Fig. 1 presents the schematic diagram of theproduct transport system and the moving mechanism of tote-boxes in it is presented in Fig. 2.

3. Results and discussion

Fig. 3 presents typical locations and simulation values ofabsorbed doses for the dummy density of 0.2 g/cm3 (sourceactivity of 280 kCi, irradiation time of 16 h). Table 1 presents thesimulation and experiment values of absorbed dose inside atote-box. The calculated values have the relative error of 1% andthe experimental values have the error of 5%. From Table 1, theMCNP calculation and experimental values are in good agreementwith each other with the difference between two data sets is lessthan 6%.

It is found that in four sides of a box there are 4 positions ofmaximum dose extremes and 4 positions of minimum doseextremes for all densities (0.1–0.5 g/cm3). For each side of a boxfaced to the source racks there are two maximum dose extremeslocated on the center vertical line at the heights of about 15 cm

Fig. 3. Simulation results of dose distribution (kGy), density of 0.2 g/cm3,

irradiation time of 16 h and source activity of 280 kCi.

ARTICLE IN PRESS

Table 1Dose values (dummy density of 0.2 g/cm3, irradiation time of 16 h, source activity of 280 kCi).

Position Surface I Surface II Surface III

Experiment Calculation Experiment Calculation Experiment Calculation

1 27.2 26.3 23.0 22.2 27.4 26.5

2 28.1 27.4 23.8 22.6 28.4 27.6

3 27.7 27.2 24.8 24.1 27.4 27.2

4 26.1 26.8 24.4 23.5 26.6 26.4

5 28.2 27.2 24.7 24.1 28.2 27.5

6 27.8 26.5 23.8 23.4 28.3 26.9

7 25.5 24.5 22.3 22.0 25.5 24.6

8 29.7 28.9 23.5 23.5 29.4 28.8

9 30.2 29.2 24.6 23.9 30.2 29.6

10 29.7 29.1 24.7 23.8 29.5 29.4

11 28.2 28.4 24.8 24.4 27.8 28.0

12 30.7 29.8 24.6 24.6 30.8 29.4

13 31.0 30.2 24.2 24.7 31.0 30.6

14 28.1 27.5 24.0 23.8 28.9 27.5

15 27.1 26.5 23.0 22.0 27.2 26.9

16 27.6 26.8 23.6 22.6 28.3 27.2

17 27.4 27.2 23.6 23.1 27.1 27.4

18 26.0 26.8 24.6 23.6 26.3 26.8

19 28.1 27.5 24.5 24.1 27.4 27.2

20 27.5 27.3 23.5 23.4 28.2 26.7

21 25.0 24.9 22.0 21.6 25.5 24.8

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

0 200 400 600 800

Positions in height (mm)

Dos

e (a

bitra

ry v

alue

)

0.1 0.2 0.3 0.4 0.5

Fig. 4. Dose distribution along the vertical central line in the middle of the box

side faced to the source racks.

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

0Positions in height (mm)

Dos

e (a

bitra

ry v

alue

)

0.1 0.2 0.3 0.4 0.5

200 400 600 800

Fig. 5. Dose distribution along the vertical central line in the middle of the box

side perpendicular to the source racks.

Table 2DUR values vs. densities.

Density (g/cm3) Experiment Calculation

0.1 1.370.1 1.3570.04

0.2 1.470.1 1.4170.04

0.3 1.570.1 1.5070.03

0.4 1.5670.1 1.6070.03

T. Van Hung, T. Khac An / Applied Radiation and Isotopes 68 (2010) 1104–11071106

and about 70 cm and they are rather symmetrical in the verticaldirection and they are not changed with increasing densities.

Fig. 4 presents the profile of dose distribution along thevertical central line in the middle of the box side faced to thesource racks.

The positions of minimum dose extremes are located in the topand bottom of two parallel sides perpendicular to the source racksat the densities less than 0.3 g/cm3 and they shifted to the boxcenter at the densities more than 0.3 g/cm3. Due to the aluminumband with the thickness of 5 mm at the bottom of a tote-box, thevalue of minimum dose extreme at the bottom of the side isalways lower than the dose at the top. Fig. 5 presents the profile of

dose distribution along the vertical central line in the middle ofthe box side perpendicular to the source racks.

Based on the results gained from experiments and calculationDUR values and averaged values of absorbed dose for the different

ARTICLE IN PRESS

Table 3Averaged values of absorbed dose rate vs. densities.

Density (g/cm3) Experiment (kGy/kCi*h) Calculation (kGy/100 kCi*h)

0.1 0.63070.03 0.62970.006

0.2 0.56570.02 0.57870.005

0.3 0.52070.03 0.53070.005

0.4 0.45870.02 0.46170.004

0.5 0.40170.004

T. Van Hung, T. Khac An / Applied Radiation and Isotopes 68 (2010) 1104–1107 1107

densities of dummies are drawn and illustrated in Tables 2 and 3.As the comparison with the calculation results, in Table 3, thedose results obtained from the irradiation of Petri dish (density of0.1 g/cm3) and sea-foods (density of 0.4 g/cm3) are presented.From Tables 2 and 3, the MCNP calculation and experimentalvalues are in good agreement with each other with the differencebetween two data sets is about 6%.

The average dose rates increase also linearly with the sourceactivity, for the four densities considered, according to theexpression Dose (kGy/h)=a* Activity (kCi); where a representsthe coefficient of linear regression. The obtained results alsoshowed that the average dose rates (in unite kGy/100kCi*h) canbe well described by a linear expression: Dose(kGy/100kCi*h)=0.69–0.58*r (g/cm3); where r is the product density.

4. Conclusions

By using experiment and MCNP code, the positions and valuesof extreme absorbed dose, DUR and averaged dose rates for somepractical densities are determined with a good agreement andvery important for the operation of the irradiator at VINAGAMMA.

The results also show that Monte Carlo simulation could beused as a predictive tool for dose measurements in an irradiatorand thus the amount of experimental work could be reducedin a large extent and could be used for irradiator designs orinnovations.

References

Briesmeister, J. (Ed.), 2000. MCNPTM—A General Monte Carlo N-Particle Transport

Code, LA 1265-M, Version 4C, Los Alamos Laboratory, USA.Oliveira, C., Salgado, J., Botelho, M.L., Ferreira, L.M., 2000. Monte Carlo application

for irradiation planing at the Portuguese gamma irradiation facility. Radiat.Phys. Chem. 57, 667–670.

Pina-Villalpando, G., Sloan, D.P., 1995. Use of computer code for dose distributionstudies in a 60Co industrial irradiator. Radiat. Phys. Chem. 46, 1385–1389.

Pina-Villalpando, G., Sloan, D.P., 1998. Dose distribution studies of a gammaindustrial irradiator using a PC code. Radiat. Phys. Chem. 52, 563–567.

Raisali, G.R., Sohrabpour, M., Hadjinia, A., 1990. A computer code for dose ratemapping of gamma irradiators. Radiat. Phys. Chem. 35 (4–6), 831–835.

Sohrabpour, M., Hassanzadeh, M., Shahriari, M., Sharizadeh, M., 2002. Dosedistribution of the IR-136 irradiator using a Monte Carlo code and comparisonwith dosimetry. Radiat. Phys. Chem. 63, 769–772.