June 28, 1951 A. C. Graves predicts that there will be more particles of 1-h size than of leu siss is offset vy the assumption that the activity carricd by @ particle is sroportional to its area. The resulting curve of activity (rceticr than number of particlcas) as a function of pore ticle diameter scems sonsible enough. (One mishit point out thet the effcet of making the activity proportional to the area rathcr than the volume of a varticle is largcly washed out by the high power of the varticle diameter introduced by the height function mentioned in the preceding paragraph). Normalization of the activity function shows that one-half of the total activity is concentratcd in particles of diameter icss than 1.1 a, where "a" is a mcan particle Size. The form in which the calevlated results are presented consists of a family of curves in which the parameter is n/a; the maximum cloud height divided by the square of the mean particle diamcter. The abscissae are reciprocals of the times at which the fall-out be- Bins, wind velocity divided by distance to the noint undcr.consideration, while the ordinates are given by the distance squarcd muitiplied into the integrated dose. Since fission fragments alonc are considered in the calculations and the t-1l+¢ decay law is assumed, one m2y find the initial dose rate by dividing the total dose obtained from the curves by 5t where "t" is the time at which the fall-out began. Some typical results are given in the tables below: Table fT Radiation ratcs at Trinity for a fit at the 2b-mile hot spot, | (Predicted mcan narticle size a= 75 p } | [ Roentgens/hour Distance Measured (Mites) | 120 0.1 | 180 0.01 j , Predicted ! 0.5 | 0,09 | ; | | 4 | | i ' : ee Table if | Greenhouse Item (Bascd on a = Op calculated from Dog fall-out on Parry) Time of Fall-out Effective (hours) | Distance | 5 10 (Miles 100 : 200 | | Roentgens/hour Moasured 0,05 + Predicted t 0.26 0.07 0.23 "| DOR ARCHIVES \ .