the fact that the broad / base of the radioactive cloud is generally stabilized at the altitude of the tropopause, which is about 55,000 feet in this area. - For the kiloton range of explosions, the lower cloud heights result in fallout coming to earth sooner and at closer distances to the point of the explosion. Although the overall area recieving fallout containation is less than for megaton explosions, this local concentration results in downwind radioactivities that can be of the same order of magnitude as the explosions in the magaton range (Glasstone, 1964, p. 457). The Test. Mike had unusually large yield and produced significant amounts of radioactivity, and so we review the early time radiation from this test (Klein, 1958). Figure 2 (labeled Fig 6 on the copy) shows the maximum activity was reached at about one hour after the explosion and that the peak activity recorded on Engebi was 100 R/hr (Roentgens per hour). The quantity of fallout at crosswind and downwind positions varied from over 20g/ft” at 4 miles to essentially zero at approximately15 miles (Heidt et al., 1953, p. 41).. Although measured at times past the peak of radioactivity, were measurements / recorded for the four-hour time after the nuclear explosion for seventeen of the most recent nuclear explosions, namely those in the Hardtack I series (Jacks and Zimmerman, 1958). 15 ee a ee aeneem