Monte Carlo simulation of the response energy distribution of proton recoil proportional counters
Congress title :International Workshop on Fast Neutron Detectors and Applications
Congress town :Le Cap
Congress date :03/04/2006
The Institute for Radiological Protection and Nuclear Safety uses proton recoil proportional counters as reference detectors for the neutron fluence energy distribution from some tenth of keV up to 2 MeV.
Several available calculation codes (like SPHERE, NRESP, GNSR,...) allowed to simulate the response energy distributions of these counters. However, these codes present some limitations due to simplified geometry of the counters, electric field effect not always taken into account and (n,p) reactions of high energy neutrons in the counter walls not considered. The use of MCNPX to calculate the proton recoil detector response matrix is a solution to reduce these limitations.
As the electric field calculation is not yet implemented in the MCNPX, its effect on the detector responses has to be calculated separately using the same method as in the SPHERE code. A graphical technique has been developed to implement the electric field lines inside the MCNPX simulation. The energy deposition into such defined cells is then weighted by the relative calculated gas amplification.
The calculated responses to mono-energetic neutron fields for cylindrical and spherical proton recoil detectors owned by the IRSN are compared with experimental data and with the SPHERE calculation for SP2 counters. The good agreement with the experimental data will be pointed out. The next step will be the implementation of the (n,p) reactions of high energy neutrons in the counterwalls.