Monte Carlo simulation of gamma-ray response functions for a proportional counter used for neutron measurement

It is often required in neutron calibration fields to determine the dose of gamma-rays produced in a neutron source and in the surroundings, because some neutron detectors are sensitive both to neutrons and gamma-rays. As a first step estimating neutron and gamma-ray energy spectra and fluences simultaneously in a neutron field, the gamma-ray response function for a 3He proportional counter was calculated using EGS4/PRESTA code. In the simulation, the gas multiplication factor, which depends on the detection position in the gas region along an anode wire, was taken into account to obtain the precise response function. For comparison, we measured response functions using different reference gamma-ray sources such as 241Am, 137Cs, and 60Co, which were located vertically 55 mm away from the center of the anode wire. Calculated response functions agreed well with experimental ones. Monte Carlo code EGS4 is thus useful for the simulation of gamma response functions for neutron counters.