Where: D t average dose rate, r/hr time after detonation, minutes This equation yields 3,700 r/hr and 1,000 r/hr as the average dose rate to be expected at 7 minutes and 15 minutes from a 100 percent-fission yield device. A vehicle, capable of carrying a radiation detector and telemetering equipment to at least the top of the highest cloud expected, was required to explore the spatial distribution of gammaactivity in clouds resulting from multimegaton detonations, It was desirable that the vehicle be able to pass well out of the top or side of the cloud, so that an indication of the contamination of the vehicle could be obtained. Because of the altitudes involved and turbulent conditicns existing at early times, manned or unmanned aircraft could not be used to measure activity within the higher regions of the cloud resulting from a megaton range device. The above, along with considerations of expense and logistic problems, indicated that a single-stage, rocket-prapelled ballistic missile would serve best to carry the detector and telemetering equipment. To serve as a basis of comparison for the activity distributions as determined by the rocket flights, theoretical estimates were prepared of the number of photons per second presentat 7 TABLE 1.1 Time THEORETICAL ESTIMATES OF CLOUD ACTIVITY Contributor Cherokee Activity, photons,’sec Zuni Navajo min 1 FP uae 29.3 «x 107 4.7% 1972 7.69x 10% r.o7x 10% 3.69 = 10” 9,13 x 10% 15 FP U8 14.8 x 107 a.7« 197 3.92% 10% 0.84107 1.89 = 10% 9,12 x 10% and 15 minutes after detonation (times at which the rocket measurements were made). The contribution to the total activity of the device components only was considered. The fission product activity, based on the slow neutron fission of U™5, at 7 and 15 minutes was found to be respectively (Reference 5). At these early times, the induced activity contribution of U"* was considered. Other induced activities with gamma energies in the range that can be measured by the rocket transducer could possibly add around 5 percent to the activities tabulated in Table 1.1 depending upon materials used in the construction of the de- vice and nearby structures. The other induced nuclides of Np** U2, Np?and U5! represented less than 1 percent of the activity due to the fission products. For capture-to-fission ratio of 1.0, the calculated activities of U7"? at 7 and 15 minutes were 4.0 d/s/10‘ fissions and 3.2 d/s/10 fissions, respectively. Applying directly the capture-to-fission ratios 0.500, 0.427 and 0.125 as determined from actual samples obtained during Shots Cherokee, Zuni, and Navajo, the contri- bution of U*"* to the total activity for the various events was then determined. The use of theoretical estimates (personal communication from C.F. Miller and N.E, Ballou, USNRDL)for the number of photons per disintegration for the fission products, 1.19, and U**, 0.83, and the num- ber of fissions per kiloton of fission yield, 1.45 x 1074 together with the d/s/10‘ fissions values for the fission products and U?"* then yielded the activity per event in photons/second at specified times. The data obtained are presented in Table 1.1. 12