DOSIMETRIC INVESTIGATIONS
OF ENVIRONMENTAL GAMMA RADIATION
FROM DEPOSITED FISSION PRODUCTS
WAYNE M. LOWDER, HAROLD L. BECK, and WILLIAM J. CONDON
Health and Safety Laboratory, U. S. Atomic Energy Commission, New York,
New York
ABSTRACT
The presence of significant quantities of gamma-emitting fission products in the environment as a result of nuclear-weapons testing has
made necessary the development of techniques for differentiating be-
tween the natural- and the fallout-gamma components of the total environmental radiation field. This has been achieved by the use in the
field of a gamma-spectrometer system with a 5- by 3-in. Nal(T1)
detector. A combination of theoretical calculations and laboratory
calibration experiments has enabled natural-gamma-radiation dose
rates to be obtained from estimated total-absorption peak areas in the
Spectra or from the total counts in bands including these peaks. The
peak method can be similarly applied to the main fallout-gamma
emitters (*Zr—*Nb, '%cs, ‘Rh, and !%Ru) to obtain their respective
dose-rate contributions. The total fallout dose rate can be obtained
from the difference between the total gamma dose rates and the natural-~gamma contribution. It is estimated that the total dose rate can be
measured to +0.5 ur/hr (standard deviation) and the individual components to +10%.
Over 300 gamma-energy spectra have been obtained at more than
200 different locations throughout the United States. Most of the inferred natural-gamma dose rates were in the range of 5 to 9 ur/hr.
Open-field-fallout dose rates between July 1962 and September 1963
ranged between 2 and 6ur/hr, except in areas having very little rain233