Development of a low-background neutron detector array

TL;DR

This paper reports the development of a low-background neutron detector array designed to measure the $^{13}$C($ extalpha$,n)$^{16}$O reaction cross section relevant to stellar nucleosynthesis, utilizing underground facilities, simulations, and efficiency calibration.

Contribution

The paper introduces a novel low-background neutron detector array with optimized efficiency and background suppression for astrophysical reaction measurements.

Findings

Achieved a background rate of 4.5(2)/hour underground.

Validated Geant4 simulations for efficiency extrapolation.

Demonstrated the importance of angular distribution in efficiency estimation.

Abstract

A low-background neutron detector array was developed to measure the cross section of the $^{13}$C($\alpha$,n)$^{16}$O reaction, which is the neutron source for the $s$-process in AGB stars, in the Gamow window ($E_{c.m.}$ = 190 $\pm$ 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($\alpha$,n) $^{16}$O reaction. The theoretical angular distributions of the $^{13}$C($\alpha$,n)$^{16}$O reaction were shown to be important in estimating the uncertainties of the detection efficiency.