Measurement of the low-energy quenching factor in germanium using an ${}^{88}$Y/Be photoneutron source

We employ an ${}^{88}$Y/Be photoneutron source to derive the quenching factor for neutron-induced nuclear recoils in germanium, probing recoil energies from a few hundred eV${}_{nr}$ to 8.5keV${}_{nr}$. A comprehensive Monte Carlo simulation of our setup is compared to experimental data employing a Lindhard model with a free electronic energy loss $k$ and an adiabatic correction for sub-keV${}_{nr}$ nuclear recoils. The best fit $k=0.179\pm 0.001$ obtained using a Monte Carlo Markov Chain (MCMC) ensemble sampler is in good agreement with previous measurements, confirming the adequacy of the Lindhard model to describe the stopping of few-keV ions in germanium crystals at a temperature of $\sim$77 K. This value of $k$ corresponds to a quenching factor of 13.7 % to 25.3 % for nuclear recoil energies between 0.3 keV${}_{nr}$ and 8.5 keV${}_{nr}$, respectively.