presumably caused by the migration of
be yo 19 /m.
the initial surface-deposited material
grated air activity {from t = 0 to o} for
239
Pu would be changed only by
into the soil,
Attempts to use the resuspension
factor approach to derive acceptable
levels of soil surface contamination have
included this “attenuation factor" as a
simple exponential function with half+
times of 35 or 45 days”? 4
There are
However, the total inte-
oo
AX 104 f exp (- 0.693t/45d) dt
°
eo
+axi0 9
exp (- 0, 693t/24, 400y)dt
0
-3
= 6.5AX 107° -3 +1,34X10°°,
major uncertainties in such a formulation,
which is an increase of 20%, and more
however.
importantly, cannot be accumulated dur-
The longest studyof this de-
crease with time extended to only 11 mo
following the initial deposition®, which
ing an individual's life span.
Because the functional nature of the
is extremely short compared to the half2395.
decrease in resuspension rate with time
life of a radionuclide such as
cannot be confidently extrapolated, pre-
There are also published reports which
viously. published models should not be
indicate on experimental and theoretical
applied to the recccupaticn of areas many
bases thet the decrease with time will
years after the contaminating event.
not be adequately represented by a single
The resuspensicn-factor approach can
exponential function, but that the rate of
be applied in an approximate way, hew-
decrease itself will also decrease with
ever, if resuspension factors are used
.
i
time’ b
Fortunately, the exact nature
which were derived from measurements
of this time dependence is not critical in
over aged sources,
determining the integrated exposure from
relevant data are unpublished results
the time of initial deposition due to the
from current resuspension experiments
fairly well-documented rapid decrease at
at the GMX site in Area 5 of the Nevada
early times.
Test Site.
However, it is obviously
Perhaps the most
The 2352p, at this location
the controlling factor for questions con-
was deposited following 22 high-explosive
cerning the reoccupation of areas many
detonations during the period from
years after the contaminating event.
December 1954 to February 1956,
As an illustration, the most conserva-
Measurements of resuspended air activity
tive published model (Kathren®) may be
levels at this site during 1971-1973
used to calculate a resuspension rate for
appear to be the only available data con239
:
cerning resuspension of
Pufroma
material 15 yr after deposition:
K 1074
-
m
exp
(83898. 15v X 365d \
TTS
45d
¥
= 10°41 /m,
source of this age,
Data irom two types or ineasurements
are available and can be used to derive
average resuspension factors,
The first
If, however, the resuspension rate
type of measurement? was accomplished
asymptotically approached some finite
by placing five high-volume cascade
value 10° § of the origina!, then the resus-
impactors”® within the most highiy con-
pension rate 15 yr later would obviously
taminated area, and running them for
4-22
tuo
an,