Figure 2: Energy spectrum of background events from one CCVR. The three prominent peaks are the 1461 keV -ray line from 40K decay, the 2615 keV -ray line from 208Tl decay, and the 5407 keV peak at the -value for 210Po decay. The 210Po peak is accompanied by a less prominent peak at 5304 keV which arises because sometimes the decay is detected but the corresponding nuclear recoil is not—namely, when the decay occurs on a copper surface facing the detectors. The livetime of this CCVR was 21.5 days, corresponding to 0.17 kg⋅y of detector exposure.