HiOR re mn city neces eRe Pan _ te ee ee 2 see ar Seetpn at * aeinen Nenana! ay ee a AS Vic spOid:.5, ocaldBat bemennretedee = werlows “mT a SscningtheTea aibility of tower shots at the swe health hagerd. . oe “Nada Proving Grounds. In the third place, the Tke maszin vody, af Sec, 2.6 conprises 2 report conctusions outlined in Sec. 2.6.11 were not ac, on fall-out that was completed just before Kem cepted as fully established by all interested shot. Certain observations on particle size of parties. The third point was discussed at a Item shot fall-out were added to this report in meeting, held several days after Dog shot, at 4, Sec. 2.6.18. There was nothing in these observa- which all professionally interested individuals tions to alter the earlier conclusions. were invited to present their views. It appeared that, at the root of the skepticism expressed 2.6.2 Summary Account about the large-particle conclusion, there lay the fact that no such large active particles had Before going into details, subsequent develbeen observed among those isolated from the opments are summarized under the following cloud samples drawn from previous shots. three subheadings. Considerable emphasis was also given to certain differences between the physical and chem2.6.2.1 Immediate Action Within a very short time, substantial evidence was brought forth that most of the activity was carried on large particles. A study of the wind soundings in the neighborhood of the shot time showed no westerly components below 20,000 ft. It was known that the fall-out started about 2 hr after the shot. The rate of fall of the particles must therefore have exceeded 10,000 ft/hr, and, by using Stokes’ law, the size was computed to be 100 microns or greater. Earth samples were collected from Parry and other islands of the Atoll; a considerable number of particles were isolated by nonselective methods; and the sizes were measured under a microscope. All particles were found to be large (details are given in Sec. 2.6.5). A record of the radiation intensity versus time was made. The general character of this record suggested the settling of a cloud oflarge particles rather than the blowing by of a cloud of small particles of which a small proportion would be expected to settle out. 2.6.2.2 Supporting Action Interest in the Dog shot fall-out was naturally widespread, and investigations were made both inside and outside the original scope of the TG 3.1 program by many individuals and projects. The following summary is confined to those investigations that were made by or at the request of CTU 3.1.5. Subject investigations were motivated by three primary considerations. In the first place, it was obviously desirable to support physical observations and calculations by biological investigations. Second, it was clear that more data were needed on the fall-out phenomenonto facilitate decisions con- ical properties of the particles isolated on Parry (Sec. 2.6.5) and the characteristics of particles isolated from previous cloud samples. The suggestion that such negative evidence was invalid, on account of the relatively smal] number of particles needed to account for Dog shot fall-out, was apparently too tenuous a counterargument to be convincing. Many other arguments were presented on both sides. It appeared desirable to seek, at subsequent shots, further evidence bearing on the presence or absence of heavy active particles in the cloud at high altitudes immediately after the shot. Direct cloud sampling with available equipment was inapplicable since it had provided no pertinent information in the past. It appeared that the best that could be done was to attempt to catch particles immedi- ately before they reached the surface. It was planned to attempt to do this where fall-out similar to the Dog shot fall-out on Parry was expected to occur, as predicted by the meteorologists. Particles so caught could not be suspected of having becomeattached to larger particles after contact with the soil. The findings of fall-out in the predicted area would, it was hoped, give convincing verification of the meteorological data and methodsof prediction. 2.6.2.3 Reconsideration of Past Information It is frankly admitted that the Dog shot fallout in the neighborhood of Parry came as a complete surprise, regarding both the early hour of arrival and the intensity of the radioactivity. It is necessary in assessing the state of current knowledge to inquire whether any earlier information had been neglected or mis-