9018993 Se properties, It was planned to use the radiochemical data from these samples to corroborate the composition of local fallout as determined from the rocket experiments, to investigate fractionation with particle size, and to compare the composition of local fallout with world wide fallout. It can not be used for determination of device partition since the sample will not represent a determinate fraction of local fallout, 1.3.5 Selection of Radionuclides, The radionuclides chosen for determination franthe particle samples were those of greatest concern in . world-wide fallout, namely sr?° and cs!37, plus a sufficient number of others to provide basic data for further investigation of fractionation. In the latter category were sr89, yl, Mo??, Cs36, Cel 44, Eu)56 and U237, The members of this group existed in a variety of forms, ranging from gaseous to relatively non-volatile species, during the period of condensa- tion from the fireball. Ca 45 was determined in conjunction with elemental analyses for Ca and Nato help in tracing the behaviour of the environmental material which forms the major part of the fallout particles. Analyses for y131, which were tentatively planned originally, were not carried out due to the limited analytical personnel available, the uncertain- ties of sample collection for this nuclide and the relatively lesser interest in its ultimate fate, SAN BREN 39