[ RadSafe ] USGS map of U.S. terrestrial radiation exposure

Jim Otton jkotton at usgs.gov
Fri Apr 25 11:08:28 CDT 2008


Earlier this week reference was made by Sandy to the USGS maps that describe
terrestrial gamma radioactivity of the U.S. at:

These maps include 1) estimated potassium concentrations; 2) equivalent
U-238 concentrations; and 3) equivalent Th-232 concentrations for surface
soils and rocks across the conterminous U.S.  The term "equivalent" is used
for uranium and thorium because the Bi-214 and Tl-208 gamma peaks were used
to estimate the uranium and thorium in surface soils and rocks.  A fourth
map shows estimated total gamma exposure for the conterminous U.S. This
latter map is derived from the other three maps by calculation.  

A brief description of how these maps were created and what the original
data source was are given.  A CD with the digitized version of the original
flightline data is available.  The flightlines were spaced 1, 3 or 6 miles
apart dependent on the geographic area of interest and what the perceived
uranium potential of the area was.  In areas of one-mile flightline
spacings, the data are very detailed and could provide reasonable estimates
of the terrestrial gamma activity component of natural radioactivity for
relatively small areas within a county.

Jim Otton
USGS uranium, radium and radon specialist 

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