Low Energy Nuclear Recoil Calibration with Neutron Capture

Ongoing experiments are searching for dark matter or coherent neutrino scattering signals via
the identification of nuclear recoils using germanium and silicon as detector materials. At the
sub-keV recoil energy scales being probed by the latest generation of such experiments, the
ionization yield of nuclear recoils in germanium and silicon is an important, but poorly
characterized, material property. A technique has been proposed to measure this yield using the
spectrum of nuclear recoils resulting from nuclear de-excitation following thermal neutron
capture in the detector crystal. This talk will present a method to measure this thermal
neutron-capture signal in germanium and silicon detectors developed for the Super Cryogenic
Dark Matter Search at SNOLAB. The measurement technique and detector principle will be
discussed as will some challenges faced in performing measurements at such low energies.
Preliminary evidence of the desired signal in a silicon detector will also be presented.