ANALYSIS OF 4-PI-GAMMA IONIZATION-CHAMBER RESPONSE USING EGS4 MONTE-CARLO CODE

The response of three types of 4 pi gamma re-entrant well pressure ion ization chambers filled with argon or nitrogen were calculated by mean s of the EGS4 Monte Carlo code as a function of photon energy and comp ared with experimental results. Excellent agreement was found between calculations and experimental results. This code was also used for the evaluation of corrections required in the change of source conditions such as the displacement of source position. In the medium and high e nergy region, the chamber response increased when the source was moved to off-center position from center whereas the response decreased in low energy region. This phenomena can be explained by a change of geom etry and the absorption of photons in an inner cylindrical absorber tu be of the chamber. (C) 1998 Elsevier Science Ltd. All rights reserved.