ever, dirt is an exceedingly poor scavenger for small radioactive particles which would be found in the mushroom cloud of an air burst, so that even though soil particles and the cloud intermingle, it does not follow that significant radioactivity due to fission products will be present in the immediate fall-out. As noted in a previous section, however, neutron induce’ activity in the soil near ground zero can result in dangerous gemma ray intensities for certain high neutron flux weapons burst over certain soils. On the other hand, a different radiological situation will be found for surface or near-surface detonations with the fireball on the ground or near enough to the ground so that soil particles will be swept up and reach a temperature that will allow radioactive fission products to be fused into or adhere to the particle. Inasmuch as the isodose rate contours resulting from such bursts have been discussed, only the influence of induced activity in bomb debris will be mentioned. The primary effect is the introduction of small perturbations in the ete decay curve from about H+10 hours to H+10 days. The radioactive decay of soil samples collected at Cperation CASTLE at the Pacific Proving Ground is shown in Figure 10. The influence of the neptunium formed from the capture of neutrons by uranium-236 is noted by the slight curve on what would otherwise be a straight line. The beta energy of neptunium-2359 is slightly higher than for many fission product mixtures so that high concentrations of the element in a sample will change the average beta energy for the sample. There is a marked effect by terrain on actual radiation intensities received. The radiation intensity above a completely smooth con- taminated plane is easy to calculate. However, a rough terrain permits the radioactive particles of fall-out to be more highly concentrated in some spots than others, as well as affording some degree of shielding. Many of the particles could fail where very little radiation effect would be seen but at the same time hot spots could occur in certain de- pressions in the terrain. This could be more hazardous than indicated 4h,