The efficiency of a helium-3 neutron detector evaluated using MCNPX

A compact neutron source based on a piezoelectric transformer has been developed as part of an on-going research effort into radioisotope source replacements for oil-well logging and non-destructive testing applications. One of the key features that will dictate the viability of the device is the effective neutron yield produced during operation. A proportional counter that uses ³He as the active sensing material was used for the purpose of detecting neutrons. The detector response to neutrons depends upon the efficiency of the ³He proportional counter tube in conjunction with the solid angle subtended by the source and the detector, as well as the material system that surrounds the proportional counter. The coupled geometry effect and energy dependence of the detector efficiency make an analytical solution prone to error. Additionally, obtaining a calibrated neutron source that mimics the size and desired activity of the piezoelectric transformer-based source was not in the scope of the research. Consequently, a numerical model of the neutron source and detector was developed and subjected to Monte Carlo analysis using MCNPX employing neutrons as the source particles. A sensitivity analysis of the detector position and orientation was used to determine the optimal location for high-sensitivity neutron counting.