The Super Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory studied energy loss associated with defect formation in germanium crystals at mK temperatures using in situ Pb-210 sources. We examine the spectrum of Pb-206 nuclear recoils near its expected 103 keV endpoint energy and determine an energy loss of (6:08 +/- 0:18)%, which we attribute to defect formation. From this result and using TRIM simulations, we extract the first experimentally determined average displacement threshold energy of 19.7(-0.5)(+0.6) eV for germanium. This has implications for the analysis thresholds of future germanium-based dark matter searches. Published by AIP Publishing.
