Localization of a "hot spot" of uranium in the lungs by an array of four HPGe detectors. The effect of variation in the isotopic composition

Modern lung counter systems which use several HPGe detectors can be used to locate a "hot spot" of uranium in the lungs by the use of vector analysis. If there is only one hot particle this localization cancels the need to assume homogenous distribution of the contamination for the calculation of its activity and enables more accurate determination of the activity of the contamination. In previous paper it was shown that the use of eight-dimensioned vectors representing simultaneously the count rates of the peaks at the energies of 92 keV (due to ²³⁸U) and 186 keV (due to ²³⁵U) leads to better results than using only one of the peaks (four-component vectors). In the present work it is shown that the possible variability of the isotopic composition of the uranium source has a major effect on the process of localization of the "hot spot" in the lungs. A way to eliminate this effect is proposed by separate normalization of the count rates of each energy peak, but still using eight-dimensioned vectors.