DETERMINATION OF PU-238 ABUNDANCE IN A PLUTONIUM METAL STANDARD BY THERMAL IONIZATION MASS SPECTROMETRY

The Pu-238 isotopic composition in New Brunswick Laboratory plutonium metal standard CRM 126-A was determined by thermal ionization mass spectrometry using combined Faraday cup and ion counting detection. A dynamic acquisition scheme was employed which provided for near real-time mass fractionation correction and ion counter/Faraday detector inter-calibration. Steps taken to minimize or eliminate isobaric U-238 interferences will be described, and an evaluation detailing contributions to the uncertainty, including SEM non-linearity, will be presented.