from the Area 11 sites at NTS and the Roller Coaster sites at the
Tonopah Test Range (TTR) have undergone radiochemical analysis.
Listed below are some pertinent findings:
1.
Th
e 239-240
Pu and
241
Am contamination levels varied from sample
to sample collected within a given activity stratum defined by
FIDLER survey instrument.
These variations were of an order of
magnitude attributable to differences in the amounts of resuspendable particulate material superficially entrapped upon plant
foliage.
The results also indicate that the activity levels
found on vegetation may be attributed largely to superficial
contamination in these aged fallout areas.
2.
Reasonable agreement occurred between the mean activity levels
of plutonium in vegetation and soil samples collected across
different activity strata within each fallout area.
The ratio
of vegetation Pu to soil Pu tended to increase moving out from
higher to lower activity strata.
3.
Results indicate a reasonably constant Pu/Am ratio for vegetation
samples collected from a given fallout area.
This ratio, however,
varied among the separate test events as the result of differ-
ences in the ingrowth of 241 am within the aged fallout source
materials.
4,
The Pu/Am ratios were strikingly lower in vegetation samples
than in soil samples from the Roller Coaster sites.
A less
pronounced trend was found in three of six activity strata
sampled in Area 13 and at the Area 11 C and D sites.
The reverse
relationship (i.e., slightly higher ratios in vegetation than in
soil samples) occurred at GMX-5 and Area 11 8B.
The real signifi-
cance of these trends is not yet understood; however, the GMX-5
site had 22 test events, while the other sites each had a single
event.
One possible explanation for the Roller Coaster sites is
that one of the more biologically available ingrowth products,
241an, has moved deeper into the root zone where greater root
239-240
uptake has occurred relative to
Pu.
Results from soil
profile samples should indicate how much movement has occurred.
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