DETERMINATION OF TRANSURANIC CONCENTRATIONS IN SURFACE SOIL AT ENEWETAK The concentrations of transuranic radionuclides (Plutonium-238, -239, -240 and Americium-241) in surface soils are determined using a sequence of procedures involving instrumental surveys, radiochemical analyses of soil samples, and statistical analysis of the data to estimate the average concentrations of transuranics in the soil. An in-situ radiometric survey of the area under investigation is performed using a unique, self-propelled instrument system called an "IMP" (named for the small tracked vehicle that carries the system). Gamma radiation from the ground is detected by a planar intrinsic germanium detector suspended from the end of a retractable boom on the IMP. Gamma spectra from the detector are analyzed and recorded. From the 60 keV gamma, the average concentration of Am-241 in the top 3 cm of soil within the detector's field of view determined... (a 2l-meter diameter circle) is Soil samples are taken and radiochemically analyzed in the Enewetak Radiation Laboratory. The concentrations of Plutonium and Americium are determined. Conversion factors are derived from these data which allow estimates of the total transuranic concentrations in soil to be calculated froma the Am-241 measurements of the IMP. To survey a large area, the IMP travels from point-to-point along a surveyed grid, making a measurement at each grid intersection. Data from the entire survey field are statistically analyzed and isopleths are drawn of the estimated average concentrations of total transuranics in the surface soil. The isopleths are based on the 70% upver bound, i.e. the probability is at least 0.7 that the true average concentration is no greater than the upper bound. If soil is removed, this process is repeated to ascertain the concentration values of newly exposed surfaces.