Development of a low-background neutron detector array

Abstract

A low-background neutron detector array was developed to measure the cross section of the 13 C(α,n) 16 O reaction, which is the neutron source for the s-process in AGB stars, in the Gamow window (E c.m. = 190 ± 40 keV) at the China Jinping Underground Laboratory (CJPL). The detector array consists of 24 3 He proportional counters embedded in a polyethylene cube. Due to the deep underground location and a borated polyethylene shield around the detector array, a low background of 4.5(2)/hour was achieved. The 51 V(p, n) 51 Cr reaction was used to determine the neutron detection efficiency of the array for neutrons with energy E n < 1 MeV. Geant4 simulations, which were shown to well reproduce experimental results, were used to extrapolate the detection efficiency to higher energies for neutrons emitted in the 13 C(α,n) 16 O reaction. The theoretical angular distributions of the 13 C(α,n) 16 O reaction were shown to be important in estimating the uncertainties of the detection efficiency.