Detection of internally deposited actinides part II: statistical techniques and risk analysis

Since a considerable number of workers at Oak Ridge National Laboratory work with compounds of transuranic elements, computer techniques have been developed to evaluate phoswich spectra in order to determine lung burdens following accidental inhalation of 239Pu, 241Am, 244Cm or other isotopes. Two unfolding methods which have been found useful in the analysis of such cases are presented and discussed. These techniques have been used successfully to detect low levels of 239Pu, 241Am, 244Cm, 233U, 90Sr, and 153Gd in contaminated workers; but because of the current importance of 239Pu, emphasis is placed on detection of that isotope in the presence of 241Am and natural human background. In the health physics tradition of emphasizing benefit vs. risk, the authors also analyze uncertainties inherent in external counting of the actinides from the viewpoint of statistical risk analysis an derive decision criteria which are useful in determining whether various radioactive species have, in fact, been detected. These criteria are somewhat different from those encountered using traditional counting statistics and derive from the realization that some errors will always be made in scanning large numbers of radiation workers. The optimum decision strategy for the determination of lung burden is, therefore, one which minimizes the long-term risk of error. The usefulness of this approach to whole body counting will be discussed and analyzed