Quality assurance associated with the preparation and analysis of samples of vegetation is now in progress for 90sr, 239°240py, 24lam, and isotopes of uranium. A sample plate of electrodeposited plutonium has been circulated among eight laboratories. Results are presented in Table 4. Since the sample was a "real life" sample from NTS, its absolute concentrations are unknown and only data The exercise checks the counting means can be given for purposes of comparison. and calcultion procedures; results are equally divided between those which might be considered high and those which might be considered low, yet all results except for one 238py analysis fall within plus or minus two standard deviations of the mean. For very precise analytical determinations, those data would indicate that recalibration at several of the laboratories should be accomplished. However, when considering the experience of the large degree of variability among aliquots of safety shot site soil, all laboratories are Each laboratory used its own counting equipment producing adequate results. and methods of calculation. Although differences are small among laboratories, it should be noted that good agreement for one radionuclide does not assure good agreement for a different radionuclide analyzed by the same laboratory. The conclusion is reached that such tests for quality assurance should include all radionuclides of project interest and not just a single radionuclide. Isotopic Determination of Uranium It is recognized that the mass spectrometer is the ultimate tool for analysis for the isotopes of uranium; however, for large numbers of samples where the high precision of the mass spectrometer is not required, a rapid, radiochemical method is of value. A radiochemical method has been developed and is now under extensive testing for the determination of the uranium isotopes 238y, 2359236y, 233°234y in soil and vegetation. Due to the low concentrations of deposited device uranium present relative to the concentrations of natural uranium in the soil, it is presently difficult to obtain reliable data for the former. If the concentration of device uranium in the soil is considered of sufficient import, more data are needed which relate to the concentration of natural uranium in the soils of interest so that the amount of device uranium can be determined adequately. The problem has been recognized by earlier investigators and is addressed by Essington et al. (1976) in their recent paper on profile studies. Site Selection Originally, the isotope of interest was plutonium; therefore, recommendations had related to safety shot sites and experiments were designed around measure- ment of plutonium. Following early recommendations, Area 13, Area 5-GMX, and Area 11 were selected as intensive study sites. The Tonopah Test Range (TTR) was later added as a fourth intensive study site (in reality, there are four discrete sites at TTR and Area 11). Although plutonium was the element of prime interest, it was pointed out by the Soils Element in 1973 (Talvitie, 1972) that the ingrowth of **!am could result in 241am concentrations being as important as those of plutonium at some future date. 29