the passage of time has generally made much more difficult, more time-consuming, and more error-prone than it was during the period shortly after the generation of the fallout. In particular, the standard autoradiographic techniques do not apply anymore: The principal fission-product activities remaining after 10 or 20 years are the strontium-90--yttrium 90 and cesium-137--barium-137 activities which comprise over 90% of the residual activity. A few percent of the remaining activity is caused by promethium-147, These activities are insufficient for adequate registration, especially since fractionation of strontium-90 and cesium-137 is quite severe, such that fallout from surface and near-surface bursts ts usually much depleted in these nuclides relative to zirconium-95 or promethium-147, or even transuranics. The fallout itself is, of course, depleted in the smallest particles. In fallout from the more deeply buried cratering shots, the fractionation pattern appears to be reversed, however. This fallout also contains little or no fused material. REFERENCES The references listed below constitute only a small portion of the available literature. They have been chosen primarily to support and to illustrate some of the statements made in the text. 1. Adams, C. E., N. H. Farlow, and W. R. Schell. 1958. "The Composition, Structures, and Origins of Radioactive Fallout Particles." U.S. Naval Radiological Defense Laboratory. Report USNRDL-TR-209. Anspaugh, L. R., P. L. J. R. Reichman, and J. Progress Report." In: Nevada Applied Ecology (Eds,). NVO-142, pp. A few methods that have been used for miscellaneous purpose are available to provide a concentration, if not a separation, of the desired particulates: density separations with or without size separations, alpha~track and/or fission-track radiography with particle isolation. These methods would be useful to provide at least a partial characterization of the contaminatio n as it exists today. There is some evidence that the transuranics were mostly concentrated in a small fraction of the fallout particulates, and although some changes in the distribution of these nuclides may have taken place as a result of weathering, this conclusion is probably still valid. Thus, a combination of data correlation and well-planned sample analysis will provide answers to most or many of the questions that are now being posed. Phelps, N. C. Kennedy, H. G. Booth, R. W. Goluba, S. Koval. 1974. "Resuspension of Plutonium: A The Dynamics of Plutonium in Desert Envtronmente. Group Report. P. B. Dunaway and M. G. White 221-310. Benson, P. A., and L. Leventhal. Fallout From Nuclear Weapons Test. Maryland. Bjornerstedt, R., and K. Edvarson. CONCLUSIONS 1s possible, the effort would be hampered by differences Prediction System." . Proc. Cont. Radioactive A. W. Klement, Jr. (Ed.). 1963. Germantown, "Physics, Chemistry, and 1966. “Department of Defense Land Fallout Defense Atomic Support Agency Reports. DASA-1800. Heft, R. A., and W. A. Steele. 1968. "Procedures for the Systematic " Separation and Analysis of Radioactive Particles From Nuclear Detonations. Lawrence Livermore Laboratory Report. UCRL-50428. Institute of Paper Chemtstry. 1960. “A Study of the Filtration and Permeability Characteristics of IPC-1478 Paper.” Defense Atomic Support Agency Report. DASA-1168. in Larson, K. H., J. W. Neel, and Associates. 1960. "Summary Statement of Findings Related to the Distribution, Characteristics, and Biological Availability of Fallout Debris Originating From Testing Programs at the Nevada Test Site." University of California at Los Angeles, School of Medicine, Report. UCLA-438. 10. Mamuro, T., T. Seiyama, T. Matsunami, A. Fujita, and K. Yoshikawa. 1962. “Electron Microscope Examination of Highly Radioactive Fallout Particles." Annual Report. Radiation Center of Osaka Prefecture 3:11. There is a significant lack of useful data on biological availabilit y. The solubility experiments that were conducted should be very critically reviewed, not only with regard to their applicability to biological avatlability, but also with regard to their validity. 244 In: Annual Reviews of Nuclear Science 13:505-534. Defense Atomic Support Agency. There exists a rather large body of data describing physical, chemical, and radiochemical properties of debris from a number of tests of different types and of interest for the characterization of the contamination of the test sites. Most of these data remain uncorrelated. Although a great deal of data correlation "Physical Characteristics of Benson, P. A., M. W. Nathans, A. Amos, and L. Leventhal. 1967. "The Density of Fallout Particles From Airbursts." Health Physics 13:1331~1335. Meteorology of Faliout." methods used, in some cases by the subjectivity of the observers/re porters. Furthermore, the objectives of the programs under which data were acquired usually did not bear much relation to each other. After correlations have been made, some inferences can be made that will be very useful for understanding the characteristics of the transuranics-containing particulates. A more definitive experimental characterization of these particulates has become rather difficult because the identification of Particles of interest by relatively simple techniques is virtually impossible as a result of radioactive decay and the partial failure by morphological and color criterta. However, the application of special methods that focus on alpha~emitters still makes far-reaching identification possible. 1964. Single Particles From High-Yield Airburst." 245