1.3 THEORY The gammaradiation emitted from a nuclear detonation may be divided into two portions: initial radiation and residual radiation. fallout and neutron-induced activity. The residual radiation may include radiation both from In this report, the radiation emitted during the first 30 seconds is termedinitial radiation, and that received after 30 seconds is called residual radia- tion. 1.3.1 Initial-Gamma Radiation. For a fission-type device the initial radiations are divided approximately as shown in Table 1.1 (from Reference 8). The major contributionsto initial- gamma radiation are from the fission-product gammas and from the neutron-capture gammas resulting from the N* (n, y) N® reaction between device neutrons and atmospheric nitrogen. The prompt gammas are nearly all absorbed in the deviceitself and are of little significance TABLE 1.1 ENERGY PARTITIONIN FISSION Reference 8s Mechanism Percent of Total Total Energy Fission Energy per Fission pet Kinetic Energy of Fission Fragments Prompt Neutrons Prompt Gammas * Fission-Product Gammas Mev 81 162 4 4 2.7 Fission-Product Betas Fission-Product : ] 8 8 5.4 2.7 5.5 5.4 11 0.1 0.2 100.0 200.0 Neutrinos Delayed Neutrons Totals eal * Mostly absorbedin the device outside the device. The fission-product gammas predominate at close distances (Reference 8). The N“ (n, y) N° gammas become increasingly important at greater distances and eventually become the major contributor. This applies only to devices with yields of less than 100 kt, in which the hydrodynamic effect is small. Figure 1.1 shows the contribution from fission-product gammas and nit (n, y) N' for a 1-kt surface burst. Therefore, the fission products become a more important source of initial-gamma exposure from high-yield fission-fusion devices at greater distances. For thermonuclear devices, in addition to gamma radiation from fission-product gammas, it is necessary to consider the interaction of neutrons fromthe fusion process with N‘*, The radiation caused by the fusion process may vary over wide limits, depending on the design of the device, For a given yield, the number of neutrons available may be 10 times as great for fusion as for fission, and therefore a large number of gamma photons are contributed by the ni‘ (n, y) N® reactions (Reference 9). However, because of the short half life, this gammaradiation decays before it can be enhanced by the hydrodynamic effect. Gammas from the longer-lived fission products are greatly enhanced by this effect. Therefore, fission products are the most important source of initial-gamma exposure resulting from high-yield fission~fusion devices. The preceding discussion is also in essential agreement with the expanded treatment given in Refcrence 10. 1.3.2 Residual-Gamma Radiation. Residual-gammaradiation consists of fission-product radiation from fallout and radiation from neutron-induced activity. 10 The decay rate of the resid-