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One of the first priorities was to establish the extent of the contamination
around the crash site and determine a zero line outside of which no
contamination was detectible.
The most valuable instrument for mapping the
contamination level was the FIDLER detector developed at Livermore.
This
instrument is designed to detect the low energy x-rays (14 keV to 20 keV) from
plutonium and the 60 keV photon from Am-241.
Because of the snow cover, the
60 keV photons from 241 produced better sensitivity and were used for
contamination contour mapping and hot-spot identification.
Thorough surveys of the contaminated area produced the {socontamination
contour map shown in Figure 1.
It was estimated that there were about 3150g
(+ 20%) of plutonium on the surface of the ice.
About 99%
of the
contamination was confined to the blackened crust where the fuel had burned.
The edge of the blackened crust was closely coincident with the 0.9 mg/m?
isocontour line.
This level is about 400 times greater than the proposed EPA
“screening level" of 0.2 uCi /m” for transuranic contamination in soil.
Snow samples were taken by Danish scientists at numerous locations (primarily
to the south and west) away from the immediate crash site.
contamination level observed was 0.4 uCi/m*.
The maximum
The geometric mean of all the
samples was about 0.004 uCi/m.
One of the major constraints in the clean up operation was that whatever
actions that were going to be taken on the ice had to be finished by the later
part of April when the ice would become unsafe to work on.
Whatever plutonium