Observation of a nuclear recoil peak at the 100 eV scale induced by neutron capture

TL;DR

This paper reports the first observation of a nuclear recoil peak at around 112 eV caused by neutron capture, providing a new calibration method for low-threshold detectors used in neutrino and dark matter research.

Contribution

The study introduces a novel in-situ calibration technique using neutron capture to observe nuclear recoil peaks at very low energies in cryogenic detectors.

Findings

Observed a nuclear recoil peak at 112 eV induced by neutron capture

Spectrum matches simulations and expected gamma de-excitation structure

Demonstrates a new calibration method for low-threshold experiments

Abstract

Coherent elastic neutrino-nucleus scattering and low-mass Dark Matter detectors rely crucially on the understanding of their response to nuclear recoils. We report the first observation of a nuclear recoil peak at around 112 eV induced by neutron capture. The measurement was performed with a CaWO$_4$ cryogenic detector from the NUCLEUS experiment exposed to a $^{252}$Cf source placed in a compact moderator. The measured spectrum is found in agreement with simulations and the expected peak structure from the single-$\gamma$ de-excitation of $^{183}$W is identified with 3 $\sigma$ significance. This result demonstrates a new method for precise, in-situ, and non-intrusive calibration of low-threshold experiments.