= : : Ne 0018933 contain1-5% of the weapon for megaton-range detonations (References 16, 46, 47). Determinations of this quantity by a world-wide network of stations for shots Mike and King of Operation IVY gave a figure of 2% (Reference 47), Some data on sr?? concentrations in the stratosphere has been obtained from filter samples collected on flights of the General Mills high-altitude balloons, This work was part of a continuing program for Sampling the stratosphere along the 80th meridian (Reference 48), 1.2.7 Fractionation Effects (I): Observations at Other Tests. The occurrence of fractionation is manifested by differences in radiochemical composition, decay rate er energy spectra among various samples of fallout taken at different times er lecations in the contaminated region. Observations of some degree of fractionatien have been made at many different detonations. sr 7? » Cs 137 As expected, fission product nuclides such as sr®?, » er Ba! #0 » which have rare-gas ancestors with half-lives of a fraction of a minute or longer, are frequently found ameng the most severely fractionated products. impertant facter. The lecation of the burst is also an Separation of the nuclides frem one another appears to be most pronounced in underground or surface shots (References 49, 50), generally less for a water surface (Reference 5!) and still smaller for balloon, high tower and air detonations (References 51, 52). Relatively SAN BRUNO FRE “a —_ | . —_ 36