STATEMENT ON RADIOACTIVE FALLOUT* 1 THE PROBLEM The testing of nuclear weapons has injected into the atmosphere large amounts of radio- active materials in the form of dust of different particle sizes. These particles descendto the surface of the earth at different rates and constitute what is known as (radioactive) “fallout.” Measurements of samples collected in different localities indicate that this radioactive material is widely distributed over the surface of the earth but with notable differences in surface concentrations. The world-wide fallout is due almost entirely to the explosion of megaton weapons which deliver fine radioactive dust into the stratosphere from which it descends slowly over a period of many years. Thus, in this case, fallout continues for a long time after the weapon has been exploded. Because of this long retention time, only radioactive substances of long half life, such as Sr*° and Cs'*", need be considered in connection with the problem of world-wide fallout in peacetime. Ionizing radiation, in sufficient amounts, is known to produce deleterious effects in living organisms including man. Radioactive fallout on the surface of the earth can deliver radiation to animals and man in two ways: (1) by the external route, in which case the penetrating gamma radiation is of chief importance; and (2) by the internal route when the material is taken into the body with food, water, and air, in which case the radiation of low penetrating power can also reach the internal organs and, in fact, is of chief concern. Therefore, the problem is to estimate what harm may possibly result to man from the general increase in background radiation and from radioactive substances introduced into the body. This requires quantitative data on the accumulation of radioactive material on the ground andin the body. Through many projects sponsored by the Atomic Energy Commission and from other sources, a great deal of information is available as to existing levels and the rates at which they are increasing. Assumptions have been made by different authorities to permit extrapolation to future levels on the basis that weapons testing will continue at the average rate of the past five years. Numerical values are constantly being revised as more information accumulates. The figures given below have been chosen by this Committee as typical ones but may not be the latest ones. It will be seen later that the general conclusions would not be altered by doubling or halving the numerical values used. 2 INCREASE IN GAMMA RAY BACKGROUND ATTRIBUTABLE TO FALLOUT Radioactive fallout began in 1945 when the first atomic bombs were exploded in New Mexico and Japan. Subsequent tests of “conventional” atomic bombs in the Pacific and Nevada also pro- duced fallout. However, in all these cases it was small in amount and more orless localized in extent. Fallout became a problem of world-wide interest after the firing of the first hydrogen * Submitted to the U. S. Atomic Energy Commission by the Advisory Committee on Biology and Medicine: John C. Bugher, Charles H. Burnett, Simeon T. Cantril, H. Bentley Glass, Shields Warren, and G. Failla, Chairman. 269