3. The Sr® activity from each test is added to the accumulated Sr® activity from previous tests. 4. For each sampling day the Sr®to total fission product activity ratio is calculated. 5. Each day’s measuredbeta activity is converted to Sr™ activity by use of this factor. This method of calculation would give high strontium values for locations near test sites on days of high fallout. This is caused by attributing the activity to the total accumulated pool of fission products rather than to the immediate burst that caused the fallout. This can be corrected by treating these few cases individually. The only practical evaluation of the new calculations technique is by comparison with radiochemical analyses of open samplers. During the period May 1956—June 1957, several locations had parallel sampling units for at least part of the time. These data are shown in the following table in which one finds that the gummed film system, together with the above method of computation, yields estimates of Sr® deposition which tend to be higher than the estimates derived by radiochemical analyses of pot samples. The mean ratio of Sr®® estimated from gummed film to pot analyses is 1.45 with a maximum ratio of 1.66 at Salt Lake City and a minimum of 0.90 in New York City. COMPARISON OF Sr® ESTIMATES FROM GUMMED FILM WITH RADIOCHEMICAL ANALYSES OF MONTHLY POT COLLECTIONS Total Periodof Location observation Sr", me/sq. mile Film/pot Monthly ratios iin/pot Film Pots ratio Low High mean New York City Pittsburgh Chicago Salt Lake City May May Dec. Dec. 1956—June 1957 1956—June 1957 1956-June 1957 1956—June 1957 12.3 12.1 6.3 15.1 13.7 10.6 4.6 9.1 0.90 1.14 1.37 1.66 0.32 0.62 1.0 1.1 2.2 2.5 1.9 3.3 1.1 1.2 1.4 1.8 Los Angeles Hiroshima Dec. 1956—June 1957 Oct. 1956—June 1957 3.5 5.6 3.1 3.7 1.13 1.51 0.78 0.82 2.4 3.7 1.4 1.7 Nagasaki Aug. 1956—June 1957 6.7 5.5 1.22 0.64 5.5 1.6 The calculation of external gamma doseis less sensitive to variations in the source of fallout. In addition, it appears that the important gamma dose from fission products is from internal Cs'*" rather than the external gamma from distributed fission products after suitable allowance for shielding and weathering. 11 cast os er