SECTION I. RADIATIONS A. GENERAL BACKGROUND INFORMATION 1. Natural Background and Medical Exposures As far as is known, man alwayshas and always will live in an environment filled with nuclear radiation. There are radioactive materials present naturally in the ground, the sea, and in the air. Cosmic rays bombard us from outer space. Naturally occurring radioactive materials in our food supply irradiate us from within. To these levels of radiation exposures are now added those from fallout—but these radiations (gamma rays and beta par- ticles) are no different in kind from those emanating from natural sources. Nor is there any evidence that they produce any fundamentally different biological effects. The radiations from natural sources and from medical, industrial, and scientific uses of radioisotopes and X-ray machines, and their biological effects, have been studied intensively for many years. To repeat, radiation exposures from fallout are in addition to those from natural sources but they are just that — additions of more of the sametype of radiation. Fallout has not introduced a new and strange agent into our environment with completely unpredictable results. Indeed, a Committee of the National Academy of Sciences-National Research Council has stated: ‘““... Despite the existing gaps in our knowledge, it is abun- dantly clear that radiation is by far the best understood environmental hazard .. .”? TABLE 1.-— Radiation Exposures from Natural Background and Medicai Sources Natural Background (annual exposures) Total... cece cece cece ec ee eee cen cee peepee eg ease een teeneneenseesen sens Gamma rays(from terrestrial sources) andcosmicrays... Potassium 40 (internal).....000 0c eee ee ence nceneeneeeeees Carbon 14.0... ccc cece ccc een eee cece saeaeeaeeseeeeesenteeseaeeeeens Medical Exposures Chest X-ray (per ExpoSure)........0....ccccceese ence eee teeter nee eee econ Back X-ray (per EXpoOSure)......0 6... ccc cee eer erence teens tenner es Photofluorogram (per exposure)............:ccceeeeeeeneeee about... Roentgens 0.085-0.20 0.1 (varies). 0.018 (varies). 0.001 0.2 0.4 0.5-2.0 Gastro-intestinal S@rieS.......0.0..0. ccc cece eee ceeceee eee ee eet eenees about... 30.