RADIATION AND MAN External Exposure While mankind has lived for probably millions of years in a naturally radioactive environment, it has only been since the creation of artificial sources of radioactivity such as bombs that X-raymachines, atomic reactors, and nuclear man-made radioactivity has presented an increased danger individually or on amass basis to man. As discussed in this report, external exposure from nuclear devices or fallout from their explosion will be mainly considered, effects are the same whether from bombs, reactor accidents, although the or medical overexposures, As mentioned before, one peculiar quality of radiation is its ability to “ionize," that is, the ability of a particle to pass through material and disrupt the atom arrangements, Particularly dangerous in the area of external exposure are neutrons and gamma rays, and can actually pass through the human body, atoms. In effect, since they are very penetrating leaving in their path ionized the thousands of these particles which pass through the human body may disrupt hundreds or thousands of atoms comprising the molecules of the body's cells--its basic building blocks, In regard to low exposure to whole-body is known, (total body) radiation, little Most data about such exposure is limited to that of from 50 rads up to thousands of rads. From 50 to about 300 rads would be considered a sublethal dose within 30 days, although at the upper end-it approaches the LD-50 range. dependent upon available treatment. death to occur; This means that it is not likely for however, within this range a number of 13 em 500211 This is also “acute” or severe effects,