Optimization of {sup 239}Pu bioassay by application of mass spectrometry

The internal dosimetry program at Los Alamos National Laboratory uses applications of Bayesian statistics in the estimation of intake dates and quantities, and associated committed doses from inhalation of {sup 239}Pu. The construction of prior distributions, based on urine bioassay results from populations of plutonium workers, has reemphasized the fact that current radiochemical techniques using {alpha}-spectroscopy do not provide detection limits that meet DOE regulations (i.e., detection of intakes resulting in a committed effective dose of 1 m Sv in the year of intake). We are in the process of constructing a bioassay analysis regimen that uses thermal ionization mass spectrometry in conjunction with {alpha}-spectrometry to optimize detection of intakes in a cost effective manner. The mass spectrometry system at Los Alamos has a detection limit of 7 gBq L{sup -1} for {sup 239}Pu in urine compared to 2 n-Bq L{sup -1} from classical radiometric methods. Results are used to construct prior distributions for worker and non-worker populations. The improved sensitivity, combined with the decision making capabilities of the Bayesian framework, provides a powerful method for detecting intakes in both plutonium workers and non-occupational populations.