CRAB - Observation of a nuclear recoil peak induced by thermal neutron capture

Abstract

Coherent elastic neutrino-nucleus scattering and low-mass dark matter detectors rely crucially on the understanding of their response to nuclear recoils. Precise calibration of this nuclear recoil signature at low energies proves to be a major challenge. Using a technique suggested by the CRAB (Calibrated nuclear Recoils for Accurate Bolometry) collaboration, a first measurement of a nuclear recoil peak at around 112 eV induced by neutron capture was performed with a CaWO4 cryogenic detector from the NUCLEUS experiment exposed to a 252Cf source placed in a compact moderator. The measured spectrum is found in agreement with simulations and the expected peak structure from the single-γ de-excitation of 183W is identified with 3 σ significance. This result demonstrates a new method for precise, in-situ, and non-intrusive calibration of low-threshold experiments.