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The application of the technique of in situ gamma-ray spectrometry to the measurement of uranium isotopes in surface soils is described. A basic review of the in situ methodology using high resolution germanium gamma-ray spectrometers is given and specifics on calculated fluences, dose rates in air, and calibration factors are provided for relevant uranium isotopes and their progeny. The influence of the uranium depth distribution on measured concentrations is examined as it pertains to the comparison of in situ results with those obtained with soil sampling. Results from the analysis of spectra collected in the vicinity of the Fernald Environmental Management Project are presented as an example of the application of the technique.

A conservative estimate of the excess total uranium in the top 5 cm of soil surrounding the former Feed Materials Production Center was made using a data base compiled by the International Technology Corporation in 1986, and the requalification of that data base was completed in 1988. The results indicate that within an area of 8 km2, extending 2 km both northeast and southwest of the Feed Materials Production Center, the uranium concentration is between 2 and 5 times greater than average natural background radiation levels. More than 85% of this excess uranium is deposited within 1 km of the site boundary. The presence of any excess uranium outside of this area is indistinguishable from the natural background contribution.