A novel method to measure low flux ambient thermal neutrons with 3~He proportional counters

摘要

A pulse shape discrimination method to discriminate neutron events from backgrounds based on the double-pulse effect of 3~He proportional counters is proposed and detailed in this paper. We made an ambient thermal neutron measurement system composed of a commercial 3~He proportional counter tube and the corresponding readout electronics. The background of the system has been measured and the minimum detectable amount of the 3~He proportional counter tube will be reduced by an order of magnitude with this method. The system was applied to measure the ambient thermal neutron flux inside a large neutron shielding structure at a deep underground laboratory and the pulse shape discrimination method proves to be effective.