Neutron spectroscopy with N$_2$-filled high-pressure large-volume spherical proportional counters

TL;DR

This paper explores a new neutron spectroscopy method using nitrogen-filled spherical proportional counters, offering a safe and cost-effective alternative for measuring neutron flux in underground labs for dark matter research.

Contribution

The study introduces a novel neutron detection technique with spherical proportional counters filled with nitrogen, capable of detecting both fast and thermal neutrons, potentially replacing helium-3 detectors.

Findings

Successful detection of fast and thermal neutrons from an Am-Be source.

Operation of the detector at pressures up to 2 bar demonstrated feasibility.

Potential for a safe, inexpensive alternative to helium-3 based neutron detectors.

Abstract

Precise in-situ measurements of the neutron flux in underground laboratories is crucial for direct dark matter searches, as neutron induced backgrounds can mimic the typical dark matter signal. The development of a novel neutron spectroscopy technique using Spherical Proportional Counters is investigated. The detector is operated with nitrogen and is sensitive to both fast and thermal neutrons through the $^{14}$N(n, $\alpha$)$^{11}$B and $^{14}$N(n, p)$^{14}$C reactions. This method holds potential to be a safe, inexpensive, effective, and reliable alternative to $^3$He-based detectors. Measurements of fast and thermal neutrons from an Am-Be source with a Spherical Proportional Counter operated at pressures up to 2 bar at Birmingham are discussed.