Internal dose estimates for workers exposed to plutonium by performing in vivo measurements of 241Am

Individual dose estimates for workers chronically exposed to plutonium is an important task in the investigation of possible health effects from internal plutonium depositions. Systemic and total body deposition of plutonium is usually estimated from urinalysis. However, this technique used alone results in uncertainty in individual dose assessment, by about an order of magnitude. Direct in vivo measurements of 241Am content in lungs, skeleton and liver by whole-body counting allows one to improve the result of dose assessment. First of all the improvement is due to the additional qualitative information about the route of intake (sorting out subjects with contaminated wounds) and solubility of plutonium aerosol particles (estimating the lung/skeleton ratio). This paper develops an algorithm for performing quantitative estimates of individual doses for workers, using the results of in vivo measurements of 241Am by whole-body counting. The algorithm applies the new ICRP Publication 66/67 models and takes into account such parameters as the 241Pu/239Pu ratio, effective aging time of mixed fission products and actinides, particle size distribution of plutonium aerosols and some other parameters. The uncertainties in individual dose assessment due to application of these parameters were analysed. It was shown that regular in vivo measurements of 241Am in the lungs allow the detection of single intake of plutonium at a level of the order of one ALI and can be a good monitoring programme for individuals involved in operations with plutonium treated in nuclear fuel cycle. (author)