Development of a Compact Flat Response Neutron Detector

Abstract

Long counters are widely used as neutron fluence monitors for their flat response. However, a bulky neutron moderator is required to achieve the flat response, which can be a disadvantage for portability and an undesirable source of scattered neutrons. Reducing the size of the moderator degrades the flat response, especially for high-energy neutrons. We propose a new method to reduce the size of the moderator while keeping a flat response, and we develop a compact flat-response neutron detector. The detector consists of two small spherical 3 He proportional counters embedded at appropriate positions in a compact cylindrical polyethylene moderator. The sensitivity ratio between the two counters was adjusted to provide a flat response in the total outputs from the two counters. We demonstrated by MCNPX calculations and response measurements for Cf and Am-Be neutrons and monoenergetic neutrons that the present detector had a sensitivity comparable to long counters with a good flat response in a wide energy range up to 20 MeV while being only one-fifth of the weight of long counters. The positions of the effective center were determined as a function of neutron energy. We also proposed a method to evaluate the neutron energy using the detector, which will allow various new applications taking advantage of the ability to measure neutron fluence and energy at the same time.Index Terms-Effective center, flat response, long counter, neutron energy evaluation, neutron fluence measurement.

Development of a neutron standard field using a heavy-water moderated 252Cf source at NMIJ-AIST

“…In this study, the ratio was 0.911, which is in reasonably good agreement with previously reported values [8]. Additional measurements using a flat-response detector [9] are also planned. …”

Research on multi-probe energy response compensation for X/γ dose rate meter

“…It could not satisfy the Chinese Standard HJ 1157-2021 [18], which stated that the relative response deviation should be between -30% and 30% in the energy range of 50-3000 keV. The use of multiple probes to optimize the response of the detector has been studied in the field of long neutron counter, and good results have been obtained, which provided an idea for solving the problem of uneven response of 𝑋/𝛾 dose rate meters [19][20][21].…”