Abstract
The U.S. Department of Energy, Nevada Operations Office, Underground Test Area Operable Unit (UGTA) is drilling deep (greater than 1500 m) monitoring wells that penetrate both unsaturated (vadose) and saturated zones potentially contaminated by sub-surface nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. Drill site radiological monitoring returns data on drilling effluents to make informed management decisions concerning fluid management. Because of rapid turn-around required for on-site monitoring, a representative sample will be analyzed simultaneously for alpha, beta and gamma emitters by instrumentation deployed on-site. For the purposes of field survey, accurate and precise data is returned, in many cases, with minimal sample treatment. A 30% efficient high purity germanium detector and a discriminating liquid scintillation detector are being evaluated for gamma and alpha/beta monitoring respectively. Implementation of these detector systems complements a successful on-site tritium monitoring program. Residual radioactivity associated with underground nuclear tests include tritium, activation products, fission products and actinides. Pulse shape discrimination (PSD) is used in alpha/beta liquid scintillation counting and is a function of the time distribution of photon emission. In particular, we hope to measure 241Am produced from 241Pu by beta decay. Because 241Pu is depleted in fissile bomb fuels, maximum PSD resolution will be required. The high purity germanium detector employs a multichannel analyzer to count gamma emitting radionuclides; we designate specific window configurations to selectively monitor diagnostic fission product radionuclides (i.e., 137Cs).
