June 28, 1951 A. C. Graves 26 The model, matched to Trinity's 25-mile hot spot, predicts higher levels at greater distances than were actually recorded at those distances and may ve considered conservative. Calculations for Greenhouse, though less convincing because of the lack of complete dose-rate contours and therefore of the exact numbers to be used, also give answers which are correct in order of magnitude, but are again conservative. Tables I and II.) 36 he. (See Surface winds are very difficult to predict over a period of hours. ‘hey are furthermore strongly affected by local terrain features, At greater altitudes, wind velocities and directions are steedier end more predictable. The path of an active cloud can be predicted with some accuracy if the cloud reaches the higher altitudes. Experience from Ranger stems indicates that a low cloud will most likely follow the valle;s. In that case the cloud would probably not disperse the 1 mile in 6 assumed in the calculations and would probably not follow a path based on local wind directions at the site except in a general sense, Mountain ridges and passes would not be effective in containing the small particles if the wind velocitywere low, With higher winds the greater local tur~ bulence would very likely increase local deposition, particularly on reverse slopes. Trapping of fission fragments in the crater is very largely off- set by the increase in neutron induced activity. There is, therefore, little to choose between one shot and another so far as total activity in the cloud is concerned. The trajectories of particles small enough to be retained in the lungs are not predictable under actual conditions. Natural air turbulence will keep such particles suspended indefinitely until they are rained out or reach the earth by some other special mechanism. At ground level, in the absence of rainout, the concentration of such particles will be dilute. Still, it is better that these particles come from a higher altitude than a lower, since the numbers of such particles at ground level and at moderate distances will depend very little on the initial cloud height while the activity contained in those from a low cloud will’ be greater. The problem of small particles is, in- cidentally, little more significant for the JANGLE shots than for any other shots already fired or to be fired in the future. For all practical purposes, the time of descent of these particles to ground level is fortuitous md beyond the range of prediction,