Specification of Radiation Field Generated by a Gamma-ray Source

Abstract

In this report are discussed the characteristics of a radiation field generated by a small gamma-ray source and the depth-dose curve in a material placed there.The experiments with TLDs and a 137Cs source resulted in a depth-dependence of about 30% decrease by aluminum wall of 100mg/cm2, to the contrary of a well-known pattern, i.e.saturation after a rapid build-up for parallel photon beam.In order to investigate the discrepancy, a Monte Carlo simulation was employed to calculate the energy distribution of the secondary electrons in an approximate geometry of a spherical source of glass sealed in a stainless-steel capsule.It was confirmed that the surface dose may be affected considerably by secondary electrons generated in the capsule and/or the air between the source and the detector. The angular distribution of secondary electrons and scattered photons have also been calculated, with which the function of a collimator was discussed.