Design Studies Of A Pulsed Quasimonoenergetic 2-keV Neutron Source For Calibration Of Low Threshold Dark Matter Detectors

TL;DR

This paper presents design studies for a pulsed 2-keV neutron source aimed at calibrating low-threshold dark matter detectors, focusing on moderator and filter optimization to achieve monoenergetic neutrons with minimal background.

Contribution

It introduces a novel design for a quasi-monoenergetic 2-keV neutron source using a scandium filter and optimized moderator geometry, advancing calibration techniques for sub-keV dark matter detectors.

Findings

Optimized moderator and filter geometry achieves target neutron flux.

Simulation shows subdominant background interaction rates.

Future plans include lower-energy calibration using time-of-flight methods.

Abstract

We describe design studies for a pulsed quasi-monoenergetic 2-keV neutron source for calibration of sub-keV nuclear recoils. Such a calibration is required for detectors sensitive to sub-GeV dark matter and also the coherent elastic scattering of reactor neutrinos. In our design, neutrons from a commercial deuterium-tritium generator are moderated to the keV scale and then filtered to the monoenergetic spectrum using a feature in the neutron cross section of scandium. In this approach, unmoderated high-energy neutrons form a challenging background, along with gammas from neutron capture in the moderator materials. We describe the optimization of the moderator+filter and shielding geometry, and find a geometry that in simulation achieves both the target neutron flux at 2 keV and subdominant rates of background interactions. Lastly, we describe a future path to lower-energy (few eV scale) calibrations using time-of-flight and sub-keV neutrons.