Radiation injury and effects of early fallout.

This is the second of four articles on the medical aspects of nuclear explosions. Last week described the blast and heat effects and explained that with modern large bombs significant radiation injury was likely to be due to fallout rather than to the radiation emitted by the explosion itself because most people subjected to the extremely short-lived initial radiation would be killed or fatally injured by blast or fire. Fallout has acquired a sinister reputation as a long-lived poison. In fact, the earth's surface is exposed to natural radiation from cosmic rays (with a higher dose the higher the altitude, since the atmosphere acts as a shield), from radioactive materials in the soil and air, and from fallout from past nuclear explosions -and this fallout now forms under 100' of total natural background radiation. In any future conflict one or more nuclear explosions will expose people in the target zone to an immediate surge of nuclear radiation and, if bombs of several megatons have been detonated close to the earth's surface, will threaten people up to 200 miles or more downwind of the explosion with radiation emitted from particles that descend as local fallout. Radioactivity in these particles will decay according to the t 1.2 formula (see last week's article). In addition the explosions will deposit some fission products in the atmosphere and residual radiation from this source will add to background radioactivity. It is the radiation emitted at the point of explosion and from local fallout that is important in producing potentially lethal radiation damage to man in the short term; and acute radiation sickness will be discussed here. The long-term effects of radiation in those who survive the acute phase and the effects of the residual radiation deposited world wide will be discussed next week.