Calibration of nuclear recoils at the 100 eV scale using neutron capture

TL;DR

This paper proposes a novel calibration method for low-energy nuclear recoils in detectors using gamma emissions from neutron capture, with simulations indicating detectable recoil peaks at 100 eV in CaWO4 and Ge detectors.

Contribution

It introduces a new calibration technique based on neutron capture gamma emissions, supported by detailed simulations and an experimental concept for cryogenic detectors.

Findings

Simulated recoil peaks at 112.5 eV and 160.3 eV are detectable in CaWO4 detectors.

Gamma tagging enhances sensitivity and extends calibration to Ge detectors.

The method provides a promising approach for low-energy calibration in neutrino and dark matter experiments.

Abstract

The development of low-threshold detectors for the study of coherent elastic neutrino-nucleus scattering and for the search for light dark matter necessitates methods of low-energy calibration. We suggest this can be provided by the nuclear recoils resulting from the $\gamma$ emission following thermal neutron capture. In particular, several MeV-scale single-$\gamma$ transitions induce well-defined nuclear recoil peaks in the 100 eV range. Using the FIFRELIN code, complete schemes of $\gamma$-cascades for various isotopes can be predicted with high accuracy to determine the continuous background of nuclear recoils below the calibration peaks. We present a comprehensive experimental concept for the calibration of CaWO$_4$ and Ge cryogenic detectors at a research reactor. For CaWO$_4$ the simulations show that two nuclear recoil peaks at 112.5 eV and 160.3 eV should be visible above background simply in the spectrum of the cryogenic detector. Then we discuss how the additional tagging for the associated $\gamma$ increases the sensitivity of the method and extends its application to a wider energy range and to Ge cryogenic detectors.