Gastrointestinal absorption of neptunium and curium in humans

The gastrointestinal absorption of Np and Cm has been determined in five male adult volunteers. The Np and Cm, which were in citrate solution, were taken with food. An initial experiment with each individual determined the fraction of each element excreted in the urine following intravenous administration. Subsequently, the results for urinary excretion for the two routes of administration were used to calculate the fractional absorption (f₁) of ingested Np and Cm. The mean f₁, values were: Np (2.0 ± 0.2) ×10^-4, range (1.2-2.9) ×10^-4, and Cm (1.7 ± 0.3) ×10^-4, range (0.95-3.0) ×10^-4, the quoted uncertainties being the standard error of the means. Currently, the International Commission on Radiological Protection recommends a value of 10^-3 for both elements. Cumulative urinary excretion over 1 wk after intravenous injection accounted for about 20%-40% of administered Np and 7%-10% of Cm. At the conclusion of the experiment, the total committed effective dose equivalent for each volunteer was calculated to be in the range 130-250 120583Sv, based on the individual f1values, and, in some cases, a knowledge of the rate of clearance of²³⁹Np through the gut as measured by whole-body counting.