(3) stabilized bare soil, that is, the cleared areas after a few days of weathering.
The
plutonium concentration in the collected aerosols changes relative to the plutonium
concentration in surface soil for the various situations. We have defined an enhancement
240
Pu concentration in the collected aerosol mass divided by the
factor (EF) as the 222+
239+240
Pu surface soil concentration (0 to 5 cm).
The EF obtained from standard high-volume air samples (hi vols) for normal
conditions is less than 1; the EF for worst-case, high-activity conditions is 3.1. Table |
summarizes the observed EF at Bikini Atoll. The EF of less than | for hi vol data for
normal, open-air conditions is apparently the result of selective particle resuspension in
which the resuspended particles have a different plutonium concentration than is observed
in the total 0- to 5-cm soil sample. In other words, the particle size and density and the
corresponding radionuclide concentration
is different
for the
normally
resuspended
material than for the total 0- to 5-cm soil sample. In addition, approximately 10% of the
mass observed on the filter is organic matter, which has a much lower plutonium
concentration than the soil. Similarly, the EF of 3.1 for high-activity conditions results
from the increased resuspension of particle sizes with higher plutonium concentration
than observed in the total 0- to 5-cm soil sample.
We have developed additional personal dosimeter enhancement factors (PDEFs)
from personal dosimeter data.
These data are normalized to the hi vol data for a
particular condition and represent enhancement that occurs around an individual because
of his daily activities (different from the open-air measurement made with the hi vols).
These data are summarized in Table |.
The total enhancement used to estimate the
amount of respired plutonium is the combination of the hi vol and personal dosimeter
values.
The
effective
enhancement
used
for
normal
conditions
is
1.54
and
for
high-activity conditionsit is 2.9.
In the scenario adopted for the calculations we assume that a person spends 8 h/d
under high-activity conditions and 16 h/d under normal conditions.
Finally, a breathing
rate of 23 m?/d (9.6 m? under high-activity conditions and 13.4 m? under normal
conditions)*! and the surface soil concentration (0 to 5 cm) for each island are used to
complete the calculation for plutonium and americium intake via inhalation.
The International Commission on Radiologica! Protection (ICRP) lung model is used
to estimate the lung and bone doses.?* A pulmonary fractional deposition of 0.3 is used in
the inhalation lung model; at this time we feel it is conservative from a dose-assessment
point-of-view because preliminary analysis of the particle size distribution for both
13