(c)
3.
in a 100-foot systematic grid near ground zero, within an
inner fence (count:
498)
(see Figure 2).
Two sampling lines where both Am concentrations in the soil and
FIDLER readings were determined, at short intervals, for the purpose
of estimating the distance--variability relationships (Figure 2).
Along each line, 15 groups of 4 adjacent soil samples were collected.
The spacing between groups is 20 feet in Line 1 and 150 feet in
Line 2.
The samples themselves are rings, 5 inches in diameter,
5 cm deep.
FIDLER readings were taken both at the surface of each
soil sample and at one foot above the ground.
Readings were taken
immediately before the soil samples were collected.
Table 1 indicates the general levels of Am activity from FIDLER readings.
Table 1.
Levels of FIDLER Activity (log, of FIDLER counts in 10% cpm
units)
Data
400 Ft. Grid
100 Ft. Grid
Line l
Line 2
Number
of
Readings
352
498
60
51
Mean
Standard
Deviation
Minimum
Maximum
0.054
0.72
0.83
-0.58
0.398
0.495
0.293
0.369
-1.0
-0.70
0.35
~1.72
1.76
2.17
1.48
~0.07
Previous studies (Gilbert et aZ., 1975) have established that Pu and Am
concentrations are in a nearly constant ratio:
Pu(x) = Am(x) x R(x)
(x:
location of sample)
(1)
with R(x) = 9.4 + 0.14 ((mean Pu/mean Am) + 1 standard deviation).
We note that FIDLER readings taken aboveground (1 foot) integrate gamma
rays within a circle 1 meter in diameter about x, weighting most heavily
the Am directly under the detector crystal.
As a consequence, the relationship between Pu(x) and FIDLER(x) (FIDLER count above x) is expected
to be more complex than in Equation 1.
Intentions
Putting Lines 1 and 2 aside, the FIDLER readings total 1,004 observations
against 174 for Pu concentrations.
In earlier efforts (Gilbert et al.,
1975; Gilbert and Eberhardt, 1974), these FIDLER data were used mainly to
370