Estimation of Effective Tissue Thickness in the Assessment of Plutonium-239 in Lung

摘要

For the determination of 239Pu deposited in the lungs by external counting, the absorption of low energy photons emitted from 239Pu in the chest must be taken into consideration because of its high attenuation.It is shown that the effective tissue thickness of the chest wall can be estimated by comparing the Am/Pu counting ratio-which is defined as the ratio of net counting rates between those in the Am-channel (57～63 keV) and the Pu-channel (15～19 keV)-obtained from an exposed subject with that obtained beforehand as a function of the absorber thickness of a simple chest model. An empirical expression was also derived from experiments on a phantom to estimate the effective tissue thickness. These two methods seem reasonably accurate judging from a comparison with the experimental results obtained by Rundo et al.