Field measurement of Cs-137 content in soil

NUCL 13

Kenneth J. Hofstetter, Donna M. Beals, and Linda S. Nichols. Savannah River Technology Center, Westinghouse Savannah River Company, Building 735-A, Aiken, SC 29808

A rapid technique has been developed to determine the Cs-137 content in contaminated soil using in-field gamma-ray spectrometry. Spectra from a 5 cm x 5 cm NaI(Tl) detector coupled to a portable multi-channel analyzer are recorded in the field, with and without shielding, to determine the Cs-137 content in a 2000 cm2 area. The field surveys take less than 10 minutes at each location. The spectral data are analyzed and compared to model predictions based on postulated source distributions. An experimental method has also been developed using a down-hole NaI(Tl) probe for determining the vertical radionuclide distribution. The results of the calculated radioisotope content compare favorably to sample results taken at the same locations. The minimum detectable activity for Cs-137 is approximately 1 pCi/gm by this field technique. A discussion of the model development and comparison of the experimental and calculated results will be given.