A method of determination of correction factors for different body builds in the assessment of Pu-239 in lung

In the determination of 239Pu deposited in the lungs of exposed subjects by external "in vivo" counting, some corrections must be made for the calibration factor obtained from a phantom, to take account of differences in body size between the phantom and the exposed subjects. Three such correction factors were considered in this work, and determined experimentally: (1) the geometrical efficiency of the exposed subject was estimated using lung-shaped plane sources of actual size; (2) the shielding effect of the sternum and ribs viewed by the NaI(Tl)-detector of large area was measured from chest X-ray plates of the fifteen subjects; and (3) the effective chest wall thickness was evaluated by means of an empirical formula. Estimations of 239Pu in the lungs are expected to contain errors up to about 24.8%, due to the uncertainities in these correction factors.