132 LOCKHART, PATTERSON, AND SAUNDERS A comparison of the overall distribution of the @ar et nuclides among the filters of a given collection2 discloses.susprisingly | little evidence of fractionation; however, the comparison of‘the,nuclide ratios of the extremes in the particle-size rdfiges showftigeTable a gives definite indications of a 90g, as aa reference, at? “t in thee Table 5— COMPARISON OF ACTIVITY RATIOS Sr FOR THE LARGEST AND THE SMALLEST-:Ss Fg. PARTICLE-SIZE FRACTIONS for initial filter vs. final filter 0.71 0.89 August 10 to 17 0.61 August 17 to September 6 September 6to 13 October 24 to November 8. Average oN 0.95 Sty §13%Ccg Ce MIpm 1.19 0.65 1.01 0.99 et 1.85 1.23 ph 1.23 1.36 a | 0.28 0.71 7 wR. 0.53 BLE nedt*O87 “ . awe ~ 6.88 0.49 0.86 - 0.83 Te ge 6.50". 76S 7 : ie: Bs - a, 87 0.41 $4 (0.23 0,52 a ae e- Standard deviatiog--Sg a of themean “#0.06 10:94:Boe:$0545 ae+0.10 at of a single rat®o nae x +0. 16 6.119 ah Standard deviation ove& - sis ppleted in the largest particles. The nuclides ‘8’cs, ‘4Ce, and te Disare rather variable in their distribution, and *'Y appears to be fractiigeag ext. There was no apparent, relation:Between the extent or dire AVtionation and the existgnce of gaseous or volatile precursors nthe, sdecay chains of the nuclifes. For example, there appeared to be no preferential as- sociation of *ty, '“4Ce, and '’Pm with the larger particles, as might be inferred from their lack of volatile ancestors. The observed association of 7!°Pb with smaller particles is to be expected on the basis of its shorter average lifetime in the atmosphere since it is continually being reintroduced through decay of the 3.8-day 72*Rn primarily in the lower levels of the troposphere. CONCLUSIONS The results obtained in these studies of the distribution of radioactivity among filters in a pack indicate that the fission-product con- glomerate encountered at ground level some months after a series of nuclear detonations has the bulk of its radioactivity associated with ie 88Sr February 15 to 21 May 3 to 10 July 19 to August 9 ee - Ratio of activity ratios to Sr =~ Collection dates, 1963 “tiers