Commissioning of a mobile neutron spectrometer for LNGS

TL;DR

This paper introduces ALMOND, a mobile neutron spectrometer designed to measure environmental neutron flux and spectrum in underground labs, aiding in background reduction for rare event searches.

Contribution

It presents the design, calibration, and initial deployment results of ALMOND, a novel mobile neutron spectrometer based on capture-gated spectroscopy with plastic scintillators and gadolinium.

Findings

Calibrated with Am-Be and Am-B sources, and D-D generator.

First neutron background measurements at LNGS Hall A.

Capture time profile analysis of neutron interactions.

Abstract

Environmental neutrons are a source of background for rare event searches in underground laboratories. Since the majority of the neutron background comes from the cavern walls due to the intrinsic radioactivity of concrete and rock, the flux is known to be time and location dependent. Therefore, a precise knowledge of the spectrum and of the total flux is needed to devise shielding and veto mechanisms for rare event searches. Here ALMOND (An LNGS Mobile Neutron Detector) is presented. It is a mobile neutron spectrometer, based on capture-gated spectroscopy and comprised of an array of plastic scintillator bars wrapped with gadolinium foils. The detector has been calibrated with Americium-Beryllium source at Karlsruhe Institute of Technology and with an Americium-Boron source and a D-D generator at ENEA Frascati. The results of the neutron calibration with the time of flight method and the D-D generator are shown here, alongside the first results on capture time profile. Moreover, the first results from the neutron background run in Hall A at LNGS are presented.