Design of a mobile neutron spectrometer for the Laboratori Nazionali del Gran Sasso (LNGS)

TL;DR

This paper introduces a mobile neutron spectrometer designed for underground laboratories, aiming to accurately measure low-level ambient neutron fluxes to improve background understanding for rare event physics experiments.

Contribution

The paper presents a novel design of a mobile neutron detector using capture-gated spectroscopy with simulation-based performance evaluation for underground applications.

Findings

Capable of measuring neutron fluxes around 10^{-6} n/cm^2/s

Effective in environments with gamma flux five orders of magnitude higher

Demonstrates potential for background characterization in underground labs

Abstract

Environmental neutrons are a source of background for rare event searches (e.g., dark matter direct detection and neutrinoless double beta decay experiments) taking place in deep underground laboratories. The overwhelming majority of these neutrons are produced in the cavern walls by means of intrinsic radioactivity of the rock and concrete. Their flux and spectrum depend on time and location. Precise knowledge of this background is necessary to devise sufficient shielding and veto mechanisms, improving the sensitivity of the neutron-susceptible underground experiments. In this report, we present the design and the expected performance of a mobile neutron detector for the LNGS underground laboratory. The detector is based on capture-gated spectroscopy technique and comprises essentially a stack of plastic scintillator bars wrapped by gadolinium foils. The extensive simulation studies demonstrate that the detector will be capable of measuring ambient neutrons at low flux levels ($\sim$$10^{-6}\,\mathrm{n/cm^2/s}$) at LNGS, where the ambient gamma flux is by about 5 orders of magnitude larger.