Ultra-Clean Underground Counting Facility for Low-Level Environmental Samples.

摘要

An underground counting facility has been designed and constructed to improve detection of low-level radionuclides. The 3.0 x 4.3 x 2.4 m counting chamber is placed 14.3 m below ground, has 10.2-cm thick walls of pre-WWII naval armor plate, and is further shielded by a minimum of 1.2 m of specular hematite. The total overburden of shielding is equivalent to 31.7 m of water. Careful selection of building materials and a special air filtering system maintain a cleanroom environment with minimum contamination potential. Background improvements are noted relative to an earlier ground-level counting chamber with 30.5-cm-thick walls of pre-WWII naval armor plate. Performance appraisals of facility detectors include a large dual NaI(Tl) coincidence system, three smaller NaI(Tl) detectors, and HPGe well detecotr, and gas proportional and Geiger counters. Major electronics for the detectors are located at a ground level control center to eliminate any associated backgrounds. Because an individual sample may be counted several days, uninterruptable power is used. An IBM PC/XT computer processes spectra from multi-channel analyzers using custom-developed software. 25 refs., 15 figs., 7 tabs. (ERA citation 13:041102)