Abstract
The excretion history of plutonium workers who acquired body burdens some 20–30 yr ago indicates that the most precisely known function for excretion (U/I = 0.0023 T−0.77, developed for a 138-day excretion period) is not valid 10 yr after uptake. To fulfill the need for a long-term excretion function, the ICRP model of a bone pool of 100-yr half-time containing 45% of the systemic burden has been used as a starting point. For excretion at times less than ∼ 1500 days, a series of exponentials has been fit to the power function above. The result is the following sum of exponentials: U/I = 0.0019 e−0.272t + 0.00023 e−0.0237t + 0.000052 e0.00303t + 8.6 × 10−6 e−0.0000190t Calculated by this equation, the excretion rate after 10,008 days would be about four times that calculated by the power function. Agreement is ± 36%(Q) with the observed excretion rate from two long-term cases, but there is an urgent need f or improvement of the function by application to many additional cases.
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