+ —e- ae a mereear main seam < ee et teeta OH whe interpreiec, nm tbe past, tests were conducted under somewhat similar conditions at Alamogordo and at Eniwetok. About 4 hr after the Alamogordo test there appeared a “hot” region of about 15 r/hr at about 25 miles from ground zero. In the early discussions of the feasibility of the Nevada Proving Grounds, this phenomenon wasattrib- uted by someauthorities to ‘‘rain-out.’’ Al- ticles are formed by the sticking of small active particles onto pieces of dirt, then it seems that some special condition or material is needed to facilitate this process, since the inactive large particles appear to be much more numerous. Without more knowledge of the way in which the large active particles are formed, it appears to be very risky to use the Greenhouse fall-out to predict the intensity of fall-out under other conditions. though others who had been present at the test persistently questioned this explanation, the rain-out theory was accepted rather widely. A 2.6.3 Surveys Subsequent to Dog Shot review of available information shows that the The effort to obtain, from subsequent shots, evidence against rain-out was in fact so strong data on fall-out comparable to that which had as to be practically conclusive. occurred on Parry after Dog shot was pushed The Alamogordo bomb was detonated on a along two lines. More equipment was put to 100-ft tower over unstabilized soil. At Operawork on selected islands of the Atoll, and protion Sandstone, the bombs were detonated from vision was made for measurements outto sea. 200-ft towers over a very different type of soil, The scope of the effort along both lines was stabilized to different degrees for the different severely limited by many factors, including shots. No comparable radioactive fall-out was shortage of time, personnel, and logistic supobserved. A review of the wind data showsthat port. the regions where fall-out might have been exInsofar as air sampling onatoll islands is pected lay outside the Atoll to the northward for concerned, no positive results were obtained. each of the three shots. No surface observaLocations had to be chosen and the equipment tions were made in this region. set up long before any reliable forecasts could For a long time there has been available be made. No significant fall-out occurred at enough information on rate of rise of the firethe locations chosen. The regularatoll intensity ball to calculate that large particles could be survey showedthat, after Easy shot, the heavicarried up to very great heights. This does not est fall-out from the upper air levels occurred prove that any specified quantity of material is in the vicinity of Kirinian. According to the in fact carried up. Even if the calculation were wind soundings, this fall-out must have ocquantitative in this respect, the degree of accurred from above 30,000 ft. Intensities were tivity of the particles, which is just as important about 1,000 mr/‘ar at H+1 hr. The fall-out as the number and size, would be very uncerfactors were similar to those of the Dog shot tain. It is understood that large particles have fall-out on Parry, and, although there were been found in cloud samples, but not large radiocertain differences that would have made one active particles. This absence of large radioexpect a moreintense fall-out, the fall-out was active particles was probably the strongest the same as that observed after Dog shot. As single factor in building up a false sense of shown in Sec. 2.6.6, the fall-out observed from security. That this negative evidence may be Runit to Bogallua was in good agreement with no better than the negative Sandstone evidence the wind soundings taken at about shot time, is indicated in Sec. 2.6.9. and many good island air sampling locations It is quite possible, however, that there was would have been available if they could have no significant amount of radioactive dirt carbeen set up a few hours before the shot. The ried to high altitudes in Sandstone clouds. The particle size distribution at 40,000 ft, as calheavy-particle fall-out observed at Greenhouse culated from the intensity survey, gave an avermay be due to the presence of some new factor. age value of about 160 microns. Following It is possible that the materials and methods George shot there was no significant fall-out on used for the stabilization of the soil around any of the islands of the Atoll. ground zero may have had a very large effect For Easy shot the survey at sea took the on the quantity of large radioactive particles which were airborne. If the large active par* ‘form of a surface survey, with air sampling ~_- a ~wee >“SPCR | ON a iy