Simple Computer Codes for Evaluating Absorbed

Doses in Materials Irradiated by Electron

Beams

T. TabataRIAST, Osaka Pref. Univ.

The 62nd ONSA Database Committee, October 7, 1996, Osaka

Contents

• Modeling of Real Configuration• Semiempirical Models for

Depth–Dose Curves of Electrons*

– Introduction, etc.– A Brief History and Principle of

the Semiempirical Models (EDEPOS and EDMULT codes)

– Applications of EDMULT– Future of Semiempirical Models– Conclusion

*Mostly from the talk given at the Int. Workshop on Electron and Photon Transport Theory Applied to Radiation Dose Calculation, Sept.18–22, 1995, Seattle, WA, U. S. A.

• Real Configuration for Electron Beam Irradiation and a Simplified Model

Real configuration

Multilayer model

Modeling of Real Configuration

• Evaluation of Absorbed Dose D

D=Ki0 vw ( )kG

K = 102 xs( ) I x,E0( )dxxw+xa

xw+xa+xs

∫ (absorbed- ,dose coefficient kGy m2 )C

xs = (thickness of sampleg cm2 )

xw = (thickness of windowg cm2 )

xa = (thickness of air layerg cm2 )

I x,E0( ) = energy deposition by the electrons

of initial energyE0 at depthx in the

(multilayer absorber system MeV cm2 )gi0 = ( )beam current in the accelerator tube A

v= (conveyor speedms)w= effective scan width at the sample

( )surface m

• Examples of Absorbed Dose

Coefficient K

SIMONS: Simonis, P. J. in “The handbook of Electron Beam Processing” (High Voltage Engineering, Vol. IND-001, 1975)

Author xw (μ )m xa ( )cmSamplematerial xs (μ )m

(1)Present work 30 8 PETPa 0 (2)Present work 30 8 PETP 100

Okabe et al. (1974) 30 8 PETP 100 (1975)Tabata 30 8 PETP 100 Proksch et al. (1979)b 25 22 Nylon 0

a .Polyethylene terephthalateb 15°.Angle of incidence was assumed to be

Comparison of EDEPOS (’96 Version) with ITS Monte Carlo

Data

Comparison of EDEPOS with ITS

Monte Carlo Data (Cont.)

Comparison of EDEPOS with ITS

Monte Carlo Data (Cont.)

• Effect of Backing Material

• Effect of the Thickness of the Air Layer

Applications of EDMULT

• Effect of Backscattering for Different Sample Thicknesses

Applications of EDMULT (Cont.)

• Quick Evaluation of Depth–Dose Curves for Many Conditions– ASTM (American Society for Testing

and Materials) Document E10.01

Applications of EDMULT (Cont.)

• Energy Calibration of Accelerators

Applications of EDMULT (Cont.)

• Improved empirical relations– Extrapolated-range formula used

in ηTN(z) and T(z) (in press)

Old equation New equation

• Improved empirical relations (Cont.)

– Inspite of many improvements, however, we use tables of data and an interpolation method for limited numbers of absorbers to get higher precision.

– Tables provided are:• CSDA range• Extrapolated range• Energy-backscattering coefficient

– Absorbers for which tables and interpolation are used are:• Be, C, Al, Cu, Ag, Au, U• A150, air, C552, PMMA, water,

WT1

• Improved EDEPOS code

– ’95 version Solid line, new EDEPOS (’95 Ver.)Dashed line, old EDEPOS (’90 Ver.)Histogram, ITSPoints, experiment from literature

• Improved EDEPOS code (cont.)

Average of δ (%)

Absorber ’96 Version ’95 Version ’90 VersionBe 1.0 2.7 13.4C 0.9 2.1 7.6Al 0.7 2.1 5.0Cu 1.7 2.7 6.6Ag 2.1 3.1 7.9Au 1.9 5.3 12.2Average 1.4 3.0 8.8

Comparison of the weighted relative rms Deviations δ averaged over energies from 0.1 to 20 MeV

δ =wi Dalg,i − DMC,i( ) DMC,i[ ]

2

i∑

wii

∑

wi = DMC,i2