June, 11, 2007 Cosmic Ray measurements using HpGe Detector

Two 30 minute long measurements were taken using the high purity Germanium detector. Although these measuements are categorized as Cosmic Ray measurements, they are really measurements of all backgrounds which the HpGe detector sees.

The Black histogram represents the rates observed WITHOUT the lead shielding plate and the Red cure is what happens when a 1" thick lead plate is placed on top of the Ge detector to shield cosmics. The integrated rate changes from 253 to 138 thousand events/day. Low energy events are clearly attenuated more. A peak at around 1.415 MeV is dimished as well and a new peak arrises at 1.450 MeV. It appears the HpGe calibration shifted during the run causing the new peak to arrise. The new peak is really the shifted sodium peak.