? Radicchemistry provides a promising apnreach to the study of particle formation. Tho mode of association of activity with the particles is reflected in the relationship between activity (per particle or per unit mass) and particle size. Furthermore, since ' the different fission. products have different chemical properties, and some have relatively long-lived gaseous precursors, they may become associated with the particles in different ways (fractionation). As a result different nuclides may exhibit, on radiochemical analysis, . different relationships with particle size. Other features such as transport end deposition of fallout ine volve meteorological conditions, which are beyond the scope of this project. 2.2 BACKGPOUND . Radiochemical fractionation has been defined as any “variation in the relative fission product nuclide abundance.1/ The phenomenon was i discovered at any early. stage of atomic weapons testing when it was observed that certain fission product ratios vary with the type and location of sample.2,3/ During the course of routine calculations of cascade impactor data’ from Operation GREENHOUSE att the authors dis~ covered that gross fission product decay was related exponentially te particle.size according to the equation, NMD = keff, where NMDeis the number median diameter, n is the slope of the gross decay curve, and k and f are constants. It therefore appeared likely that radiochemical fractionation wes primarily a function of particle size distribution in a sample. Operetion JANGL® afforded an opportunity to study fractionation in greater detail. Size-graded fallout from the underground shot was investigated radiochemically.5/ The specific activity of several nuclides was found to vary regularly with particle size, in the range from 50 to 70 p. Different nuclides were found to be distributed differently in the particles, e.g., Sr°9 on the surface and 2r95 in the bod; of the particle. A theory was proposed based on the existence of gaseous precursors, Similar ideas have been discussed by Cadle6/ and by Adams et al.7/ . A sirilar investigation was undertaken at Operation IVY (Bouton et a18/) for particles in tha range from 70 to 220 yp for the study of a greater number of nuclides than at JANGLE. The analysis was seriously hampered by the presence of a large quantity of water in the fallout samples. Certain nuclides were selectively dissolved in significent amounts and contaminated the inactive particles. As a result no reliance could be placed on figures for the ser cent. active particles, which are necessary to correct the specific activities. For this reason the rediochemical data have thus far defied theoretical interpretation. They did sugg2st some strong possibilities, however, It appeared likely at the tire that M099, like Sr89, was deposited on othe surface of particles, possible as a result of the volatility of Mo? under the high temperatures associated with thermomclear experiments. 15 SECRET — RESTRICTED DATA i ;