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DIETARY RADIOACTIVITY INTAKE FROM BIOASSAY DATA
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subjects. The following section summarizes
the development of a mathematical model
which relates body burden, urinary activity
excretion rate and daily activity ingestion rate.
An understanding of this latter parameter is
crucial to the predictive modeling of dose
commitmentsto people living in contaminated
environments such as that at Bikini Atoll.
“METHOD
Appendix A of ICRP Publication 10A
(ICRP71) describes the relationship between
body burden, g(t) and activity excretion rate
E(t) at some time ¢:
E(t)=k q(t)
where
k=the
instantaneous
(1)
fraction
of
activity leaving the body per unit time, d7’.
Thus, E(t), the activity excretion rate, is
directly proportional to the body burden,
q(t). With this equation, either q(t) or E(t)
can be calculated from a single bioassay
measurement provided that (1) the mean
residence time of the radionuclide in the
body, which bydefinition is the inverse of the
total removal rate constant for the radionuclide, is known, and (2) the excretion rate can
be described by a single rate constant.
Similar equations are developed here to
determine the daily activity ingestion rate for
'7Cs assuming that two compartments in the
body release °’Cs radioactivity to the urine.
These equations assumea constant continuous
uptake during the whole body count and
urinary sampling interval, and relate the constant continuous daily activity ingestion rate,
AP, to the measured body burden at time of
measurement, and the umnary activity
excretion rate one day later.
The equations have been developed using
mae