Cross country background measurements with high purity germanium

Background measurements were made with twenty-eight high purity germanium detectors (HPGe) on the Mobil Imaging and Spectroscopic Threat Identification (MISTI) system across a portion of the Continental United States (CONUS). MISTI was developed by the Naval Research Laboratory(NRL) for the Domestic Nuclear Detection Office (DNDO) as part of the Stand off Radiation Detection Systems (SORDS) program. Measurements were made from Washington D.C. to Pocatello, Idaho, during the dates of Mar 25, 2011 to Mar 28, 2011. The effect of variable backgrounds on detection sensitivities will be discussed. An opportunity was also afforded to measure the radioactive materials released from Japan's Fukushima I Nuclear Plant across a significant portion of CONUS. A description of the instrument and results are discussed.