70 MILLER AND SARTOR value of C for the larger fallout pattern could then be calculated if the yield were known. A commonly used value of K} in Eq. 7 for estimating the fraction of a devicein the fallout pattern, especially when experimental values of Dq are not directly available, is 2000 r/hr at 1 hr per kiloton per square mile. If this value is used with the Jp value, 1460 r/hr at 1 hr per square mile, for the Small Boy fallout pattern, the estimated value of Fp could be compared to that obtained through use of the radiochemical analysis of the fallout material and the methods outlined in this report. COMMENTS AND CONCLUSIONS The computed l tp values appear to be somewhat low, especially for the median particle diameters between about 200 and 800 yu. Further examination of the radiochemical data with respect to the fractionation of individual nuclides and to the fission yield of *Zr, as a measure of the number of fissions, could provide further information on the ry, values. The major factors in determining the Vip values, if the data from ion-chamber measurements are accepted as being by far the most accurate, are the fission content of the samples and the decay factors from 100 to 1 hr after detonation for the ion-chamber data. The absolute value of i) for the unfractionated mixture of radionuclides from thermal-neutron fission of **U rather than for fission by fission neutrons would result in a relatively small error in the r,, estimates. It should be expected that the decay factors for the samples would approach those for iy as the r;, (100) values approach unity, indicating a relatively unfractionated mixture of radionuclides. The Dq values derived from the data are consistent with other previously derived values of q for the Nevada Test Site terrain.’ These values generally would not be influenced by possible future changes in the r,, values since any change in r,, would result in an equivalent change in the values of the K). The example analysis of some of the Small Boy shot data applica- ble to evaluation of the intensity—activity ratio shows that the ratio is not a constant for a given fallout pattern but varies over the pattern depending on the particle sizes in the deposited fallout. However, when gross activity—size distribution data are evaluated, an average value of the ratio can be derived for the fallout pattern. On the other hand, the average value of the intensity—activity ratio is not required for estimating the fraction of the device within a fallout pattern. A value for this ratio for the fallout deposited uniformly over an ideal plane, an average terrain attenuation factor, and an instrument response factor, however, are needed for estimating the fraction of device in the pattern.