16,000 i PLANT ACTIVITY, MUC / GRAM DRY WEIGHT a ,,.,i 1964] MARTIN : RADIOECOLOGY AND STUDY OF ENVIRONMENTAL RADIATION 301 In most loeal fallout patterns, the unit area activity and the mean particle size of fallout deposited on fallout collectors and/or on soil surfaces have been found to decrease with increasing distance from ground zero and i _ (Vou. 91 with increasing time of fallout deposition. Concurrently, there is an increase in the percentage of total activity associated with particles < 44y in diameter (Table 6). In general, the radioactive materials associated with smaller fallout particles are more readily soluble in distilled water and in dilute acid than are those associated with larger fallout particles. As much as 90% of the activity associated with fallout particles < 44, in diameter may be soluble on 0.1 N HCL. The local fallout from balloon-supported detonation Table 7. Soil and plant contamination in relation to distance from ground zero and the particle size composition of fallout. Detonation Apple IT, 1953 Smoky, 1957 Miles from Ground Zero Miles from Midline 7 0.6 48 0.8 Particle Size: < 44y 0.1 (% of beta activity in size range) 15.3 71.7 21.1 41.8 NS 82.5 NS 44-88 > 88u Fallout on Soil Fallout on Plants: Red Clover* Wheat* Alfalfa** Mixed grasses** % Interception by Plants: Red Clover Wheat Alfalfa Mixed grasses 0.1 99.8 2070 2.35 4,14 NS NS 0.11 0.20 NS NS 106 34 2.2 4.0 24.3 132 9.5 TL 7.7 205 0 55.1 3.0 (u ¢ beta activity per square foot) 636 20 75 133 (4 ¢ beta activity on plants per ft? of soil) 4,22 15.09 NS NS 0.25 1.16 NS NS NS NS 3.7 NS NS NS NS 5,0 (soil activity/plant activity x 100) 0.66 125 NS NS 2.37 NS NS 5,80 NS NS NS 4,93 NS NS NS 3.75 259 3.5 NS 85 NS NS 9.9 4.5 NS NS 1L.74 5.32 * Grown on soil flats and prelocated on D-1 day. ** Collected from farms in fallout area. NS=No sample. After: Romney et al. (1963). has been found (Larson et al. 1960) to be composed primarily of < 44p particles, and this size fraction was found to contain relatively higher concentrations of Sr-89, Sr-90, Y-91, Ru-106, and Ba-140 but less Zr-95 and Ce-144 than larger size fractions. 20 und zero and ided by the viously de- 2. Plants. Studies of soil, plant, and animal contamination were made during Operation Teapot in 1955 (Lindberg et al. 1959) and during Operation Plumbbob in 1957 (Larson et al. 196°). The results of the plant contamination studies have been summarized recently by Romneyet al. (1962). Their summary is briefly reviewed below. It has been established by autoradiographic and microscopic examinations of foliage exposed to fallout that Jeaves in general are selective collectors of fallout particles < 100 in diameter. Tallies of the size and number of *