Ca
wi.
resuspension factor by the exponential function:
exp (- 0.693 t/l5 days).
There are major uncertainties in such a formulation,
however.
The longest
such study extended to only eleven months following the initial deposition’,
which is very short compared tc the half-life of a radionuclide such as
u.
My own belief is that this half-time increases with the passage of time.
Otherwise, after fifteen years following deposition, a 45 day half-life would
reduce the resuspension factor by ro,
Data will be presented below which
Clearly indicate that this is not true.
There are some values in the literature for resuspenion factors of aged
material.
Mishima quotes values of 6.2 x 1072? to 1073/m for aged plutonium
deposits at NTS.
These measurements were apparently made 16 months after the
initial deposition”.
Perhaps the most relevant data, however, are unpublished results from the
resuspension experiments at the GMX site in Area 5 of NTS.
The 239pu at this
location was deposited following 22 high-explosive detonations from December,
1954, to February, 1956.
Measurements of resuspended air activity levels at
this site during 1971 — 1973 appear to the only available data concerning
resuspension of 239, from @ source of this advanced age.
Two kinds of measurements are available which can be used to derive timeintegrated averages of resuspension factors.
First, five Andersen hi-volume
cascade impactors were set up within the most highly contaminated area, and
were run for 36 days, from July 7 to August 12, 1972!.
he collected 2395,
was lognormally distributed with particle size with a geometric mean of
3.2 +13 um.
The 2395 concentration varied from 0.023 tp 0.087 apm/m> with
an average of 0.052 dpm/m- for the five samplers.
At the present time onlv
limited data is available regarding the soil activity in the area.
Four