0018933 CS evidence that the nuclides in the larger particles (3-12 p) were fractiona- ted, but those in particles smaller than | p were not (Reference 54). TM This method of data analysis has been shown to be valid regardless of the secondary reference nuclide, the primary reference nuclide and the reference event (Reference 6 }, 7 N\ 1,3 EXPERIMENTAL PROGRAM 1.3.1 Outline of the Program, The foregoing discussion indicates that further progress in the development of a realistic fallout model will require an improved knowledge of the structure of nuclear clouds with respect to the vertical and radial distribution of particle size and radioactivity within the mushroom, Quantitative data on the activity associated with particles in different size groups is also needed for estimation of the partition of the weapon between local and world-wide fallout. Project 2,8 was established to attempt to obtain such information from certain shots at Operation HARDTACK, It was planned to explore the cloud structure by means of air sampling rockets and to use both the rocket samples and also aircraft samples collected from the cloud with the UCRL coincident sampler for determination of the fallout partition. Other aircraft flying at 1000 feet were scheduled to collect fallout samples te be used for the determination of the effect of particle size on fractionation and for corroboration SAN BRONO rR