Neutron-induced activity in the soil has been a subject of considerable study. In sandy soil, radiosilicon may be formed with a 170- minute half-life, emitting a 1.8 mev beta but no gamma, decaying to stable phosphorous. In clay soil, radioaluminum may be formed with a 2.4 minute half-life, emitting 2.7 to 3.3 mev betas and a 1.8 mev gamma, and decaying to stable silicon. In the coral sand of the Pacific Proving Ground a considerable quantity of calcium-45 may be formed. Its relatively long half-life of 180 days, a 0.26 mev beta with no gamma, and its position of importance in the biological system, make it interesting. However, the quantity formed by detonation of a weapon over average soil would not result in a sufficient amount of calcium-45 to constitute a hazard. Radiosodium may be formed in areas where the concentration of sodium is high, and this may become importent in detonations over and in sea water. It is the considered opinion of most investigators that forornear-surface bursts, induced radioactivity in elements of th 1dwater is of minor importance ee to the over-all fall-out hazard, particularly so after the first day following the detonation. The area where ground induced activity may importantto the area around ground zero. The amount of activity formed depends upon the type of bomb, height of burst, and type of soil over which the detonation occurred. Neutron-induced activity in the ground is apt to be of greatest importance when the weapon is burst in such a position that the fireball is just clear of the ground. In this case, there would be very little fission product activity deposited locally, as will be discussed later; however, the induced activity at ground zero might be as much as 2000 r/hrat one hour after burst time for certain high neutron flux weapons such as " "Tt 4s important to note that the t~/°= redioactive decay ‘factor discussed previously would not be applicable in this case. The early decay would be apt to be slower but the later decay would be faster then the t/°= formula would indicate. For example, high sodium ccutent in the soil would probably give an effective half-life of about 10