and Its Application to Radiation Shielding Studies

*1High Energy Accelerator Research Organization

*2Kyoto University

Electromagnetic cascade Monte Carlo code EGS4, which was developed by W. R. Nelson, H. Hirayama and D. W. O. Rogers, is the most widely used code in the field related to electron photon transport calculations. The EGS code system started from high energy applications. Therefore, low energy electrons and photons are not correctly treated. At the stage of EGS4, several improvements were performed concerning treatments of low energy particles but still several subjects to be improved are left behind.

Following improvements for low energy photon transport were performed at High Energy Accelerator Research Organization (KEK) to extend the energy range of EGS4.

- Introduce polarized Compton and Rayleigh scattering which affect to the azimuthal angular distribution
- Introduce Doppler broadening at Compton scattering which affects to the energy distribution of a scattered photon and electron
- Improvements for treatments of K and L-shell fluorescence including general treatments for compounds and mixtures.

The effects of polarization and Doppler broadening are well known physical phenomena but are not included in the general purpose photon transport code before.

Series of experiments were performed using mono-energy photon beam at KEK Photon Factory to check the accuracy of the improved EGS4. Calculations with improved EGS4 were compared with measured results in the absolute basis and agreed very well.

The improved EGS4 were applied to radiation shielding researches such as gamma-ray buildup factors and line bean response functions for gamma-ray skyshine.

Gamma-ray buildup factors are the basic data of the point kernel method which is used widely at the practical shielding calculation. Improved EGS4 is used to study the effects of polarization and Doppler broadening and to provide both for single and multilayer buildup factors up to 40 mfp by using a kind of splitting technique. EGS4 results are used as the reference data to check buildup factors calculated by the other method like a discrete ordinate.

Systematic studies concerning multilayer buildup factors were performed to make up the parametrisation method of multilayer buildup factors. The new simple description formula applicable to wide energy range and variety of material@ combination was developed using the EGS4 result.

Gamma-ray line beam response functions are the another basic data used at the skyshine dose calculations. EGS4 was used to calculate the line beam response functions from 300keV to 10MeV for various emitted angles and also to study the feature of the line beam response functions comparing with those obtained by the point kernel code, G33. The produced line beam response functions are replaced with the original ones in the SKYSHINE code to study the effects of response functions.

EGS4 Users' Meeting in Japan is organized from 1991 at KEK to exchange the experiences at the researches using EGS4 in various fields. The Proceedings of this meeting include the very useful information for the researchers related to electrons or photons not only EGS4 users and are, therefore, requested from all over the world.