The Origin of Low-Level Airborne Radiometric Anomalies in the Copper River Basin Region, Alaska Page: i
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Several low-level radiometric anomalies had been detected in an
airborne survey of the Copper River Basin. This report presents the
results of field and laboratory research on the origin of the anomalies,
and the low radiometric background of the Copper River Basin.
Intrusive igneous and sedimentary rock types in the study area are
relatively depleted in uranium, as compared to worldwide averages; and
the lowlands and foothills are covered by muskeg-mantled less derived
from glaciofluvial deposits. Therefore, most outcrop or rubble crop has
a higher radiometric signature than the surrounding silt-covered terrane.
In at least one case, terrace gravels also have a higher radiometric
signature than the adjacent tundra.
The highest radiometric values were obtained for altered tuffs in
the Sanona Creek area, and quartz monzonite on Flat Top Mountain. In
both cases, however, actual uranium concentrations were lower than
worldwide averages for similar rocks.
The Geometrics GR-410 gamma spectrometer gave poor reproducibility
on successive counting runs on uranium/thorium-poor rocks. When K40 was
the major source of radiation, counts recorded on this channel were
frequently greater than those recorded on the total channel; a disparity
which indicates that the GR-410 may have been operating at uranium/thorium
concentrations which were lower than reliable detectability and counting
thresholds for this particular instrument.
Replicate uranium analyses indicate that neutron activation is
superior to standard wet analytical techniques, and that the latter
values tend to be consistently low as compared to neutron activation
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Forbes, Robert B.; Carden, John R. & Zdepski, J. Mark. The Origin of Low-Level Airborne Radiometric Anomalies in the Copper River Basin Region, Alaska, report, May 1977; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc784612/m1/3/?rotate=90: accessed December 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.