CHAPTER 17 interaction of the gamma rays with particles in any medium (including air) results in diversion of the radiation from its initial path and in loss of energy (Compton effect). The amount of attermation is de- pendent on both the energy of the incident rays and the density of the material traversed. The higher the gamma-ray energy, the less the attenuation for a given density; conversely, the higher the density of the medium, the greater is the attenuation for @ given gamma-ray energy, particularly for the energies of F.P.C. gamma reys and ship materials. The effect of decreasing the density of material (where the material is air) between the source and target is illustrated in the enhancement of fission-product gamma radiation noted for megeton-yield bursts. F.P.C. gamma radiation at a particular distance scales linearly with yield for land surface bursts up to about 100 KT; however, progressively greater-than-linear scaling with increasing yield is noted for megaton- yield bursts. This enhancement is partially due to the greater amount of gamma rediation resulting from inelastic scattering and nitrogen capture of the neutrons produced in a fusion detonation, and partially to the "hydrodynamic effect," in which the shock wave produces rarefaction of the atmosphere, eliminating much of the air attenuation for the fission product gamma rays. The velocity of the shock front for highyield bursts is sufficiently higher than that for low-kiloton-yleld bursts to producg ,a significant enhancement of the F.P.C. fission-product gamma radiation. The source-to-target distance, the angle of incidence of the radiation, and to an extent the ship orientation to the burst are of significance in calculations where source-shield geometries must be considered, such as for locations within a ship where the hull and decks act as attenuating shields for the radiation. The greater the sourceto-target distance, the more the radiation will be scattered. Scattered radiation is more greatly attenuated by a shield than is direct radiation, because its energy has been reduced by scattering. The angle of incidence of the rediation is significant because radiation incident on the "shield" at moreoblique anglé@s traverses greater thicknesses, hence is more atten- uated than radiation following the shortest path. In addition, the ~ radiation will have to traverse greater thicknesses of the ship's structure to reach interior locations if the ship is bow-on or stern-on to the burst than if it is beam-on. 17.4.3 Field-Test Fireball-Plume-Cloud Radiation Data and Estimates of Free-Field Fireball—Plume=—Cloud Radiation Dose (1) F.P.C. Neutron Radiation. Little neutron radiation data from water-surface bursts is available, and most of the estimates have been based on data from land-surface, tower, and air bursts. At Operation Hardtack, neutron flux measurements were made at two of the barge shots. Examination of the neutron flux curv energy ranges) for shots Yellowwood that the slopes of the flux-vs-dist e various de (various and Walmt‘ie: curves are not e. However , the differences may have been due to the positioning of the BEST AVAILABLE COPY 17-23