factors are operative in determining the total exposure received from ee nna cae ie ae eee fallout. One example of weathering effects was after the March 1, 1954 fallout on the Marshall Islands in the Pacific. Figure 4 shows| the gamma dose rates on the Island of Rongelap over '# period of about two years. In the first ten days when the winds were light and there was no rainfall, the decrease in activity was roughly consistent with known radiological decay rate. The break between the tenth and twenty~ fifth day undoubtedly represents the effects of rain which was known to have occurred in that period. Figure 4 suggests, however, that any further reduction in contamination by rainfall was slight. An example of the effects of winds, occurred after one of the nuclear detonations at the Nevada Test Site in 1953. Strong winds blew almost at right angles across a narrow band fallout field on the 2nd and 3rd day after the detonation. The gamma dose rates at three feet above the ground on the 4th day were less than predicted by the relationship of (time)-l-2 by factors ranging from three to six, while the activity of the soil samples collected on the first day and taken into the laboratory did decrease approximately as (time)-1.2, This effect of winds would not be expected to be as great for large contaminated areas of non-sandy soils. | Calculations of shielding and attenuation factors for different types of materials and theoretical calculations for various structures are plentiful references through 11 (Table 1), but more information based on actual field experience is needed. Limited . t.