During this period, research efforts were directed to two areas of study. First, analyses were completed of plutonium distribution among particle size fractions of three additional samples taken along the north-south transect. Second, particle size segregation and plutonium distribution in the different sizes of two closely situated samples were completed--one located in the bare area of the desert, the other beneath a saltbush 4 ft away from the first. The additional three samples along the north-south transect were included because the distance between the previous consecutive sampling points 6 and 7 was 3,200 ft; and beyond point 7, the distance was 1,000 ft. For a better understanding of the plutonium concentrations in the surface soils as a function of distance from the point of detonation (GZ), more data points were desirable. The study of the two closely situated soils was initiated to determine differences, if any, in the plutonium distribution under these two different conditions. EXPERIMENTAL METHODS Quantitative analysis of plutonium was made using the hot HNO. -HF technique, as described earlier (Tamura, 1975b). The technique used for particle size segregation of the NTS soils has also been described previously (Tamura, 1974). It should be mentioned that in the segrega- tion treatment normally applied to these soils, no dispersant or vigorous mechanical treatment is used. However, in the two samples taken adjacent to each other, one aliquot received the usual treatment and a second aliquot received a 5-min ultrasonic treatment to induce dispersion. A‘Blackstone ultrasonic vibrator equipped with a 1/2 in. probe was used.