Development of position sensitive ³He proportional counter for a single moderator type neutron spectrometer

A position sensitive ³He proportional counter with 1 m length was developed to use for a single moderator type neutron spectrometer, which measures neutron spectrum from the depth distribution of thermal neutrons in the moderator. The counter is of the charge division type using an anode wire with resistance. The detection positions can be determined from the ratio of the pulse heights read out from both ends of the counter. The inner diameter and composition of the counting gas were optimized with a simple Monte Carlo calculation code. From the optimization the inner diameter of 25 mmφ and the mixed gas of 130 kPa ³He and 70 kPa CF₄ were adopted. A relationship between the detection position and the ratio of both pulse heights and a spatial resolution were measured using thermal neutrons. The relationship has a one-to-one correspondence. The spatial resolution was evaluated to be less than 10 mm all over the sensitive area, and the value is small enough for the spectrometer. (author)