© FOR OFFICIAL USE ONLY fall-out in the United States Following nuclear detonations, radioactive debris is distribute? by normal air currents over large areas, and with sufficiently sensitive instruments may be found to encirele the globe. ‘Small ammunts were deposited widely over the United States during the Pacifico tests and in sone areas resulted intramsitory rises of the normal background radiation levels. Transportation of the radioactive materials to the United States took only several daya. Thus some of the shorter half-life radioisotopes, such as Iodine 131 (8-day half life), were still present in the fall-ovt. the amounts were biologically insignificant, it was Although ypesslble, by spacial techniques, to demonstrate radioiodine in the thyrald glands and in the urine of grazing animals. Extremely minute quantities of Indine 131 vere also datectable in the urine of some humans for a short tims. The radioactive isotopes to be found normally in the body are potasaium 40, carbon 1, and radium 226. The radiopotassium and radiocarbon are distri- buted throughout the tissues while the radium is almest entirely lecated in the skeleton. In addition to this internal irradiation, man is subjected to cosmic rays from without and to the gamma reys fram radium in the soil. this natural exposure, tha radiation from bemb products is added. To The point of interest in terms of health lies not in the mere presence of radio- isotopes, but 3m the amounts and more specifically in the quantity of rad4ation deeee delivered by these radioisotopes. The levols of activity from fall-out, outside the area surrounding the Pacific Freving Grounds, have been far less than amy required to produce detectable injury either from the radinisotopes within the body or from external radiation. FOR _OFFICI4L USE ONLY 8 i i i : 4 . ee B. r eB g 4 ‘ é * ~ a oie ee