contribution of other exposure pathways, such as inhalation of contaminated air and consumption of contaminated water and food, to the total radiation dose received by humans.

Radiation has both acute and latent health effects. Acute effects include radiation sickness or death resulting from high doses of radiation (greater than 1 sievert [Sv], or 100 rems) delivered over a few days. The principal latent effect is cancer. Estimates of latent cancer fatalities are based largely on results of the long-term follow-up of the survivors of the atomic bombings in Japan. The results of these studies have been interpreted by the International Commission on Radiological Protection (ICRP)1 in terms of a lifetime risk coefficient of 0.05 per sievert (5 × 10−4 per rem), with no threshold.2 For the present study, acute radiation effects were estimated by both DTRA and LLNL; latent cancer deaths were estimated only by LLNL.

The computer models used by DTRA and LLNL were developed primarily to estimate effects on military personnel rather than for civilian populations. Thus, there is no consideration of the presumed greater sensitivity to radiation of the very young and the elderly. Also, there is no consideration of the sensitivity of the fetus. From the experience in Japan, it is known that substantial effects on the fetus can occur, and these effects depend on the age (stage of organogenesis) of the fetus.3 One such effect is mental retardation. The transfer of radio nuclides to the fetus resulting from their intake by the mother is another pathway of concern. Radiation dose coefficients for this pathway have been published by the ICRP.4

Another long-term health effect that is not considered here is the induction of eye cataracts. This effect has been noted in the Japanese studies and also in a study of the Chernobyl cleanup workers.5

Compared to the fatalities from prompt, acute fallout and latent cancer fatalities, the absolute number of effects on the fetus is small and is captured within the bounds of the uncertainty. The number of eye cataracts, based on the experience of the Chernobyl workers, is not small. The occurrence of eye cataracts in the now aging Japanese population is several tens of percent among those more heavily exposed.

Finally, there has been a recently confirmed finding that the Japanese survivors are experiencing a statistically significant increase in the occurrence of a number of noncancer diseases,6 including hypertension, myocardial infarction, thyroid disease, cataracts, chronic liver disease and cirrhosis, and, in females, uterine myoma. There has been a negative response in the occurrence of glaucoma. A nominal risk coefficient for the seven categories of disease is about 0.9 Sv−1 (0.009 rem−1). The largest fraction of the risk is due to thyroid disease.

Thermal Radiation from Underground Bursts

Thermal radiation may make fire a collateral effect of the use of surface burst, airburst, or shallow-penetrating nuclear weapons. The potential for fire damage depends on the nature of the burst and the surroundings. If there is a fireball, fires will be a direct result of the absorption of thermal radiation. Fires can also result as an indirect effect of the destruction caused by a blast wave, which can, for example, upset stoves and furnaces, rupture gas lines, and so on. A shallow-penetrating nuclear weapon of, say, 100 to 300 kilotons at a 3 to 5 meter depth of burst will generate a substantial fireball that will not fade as fast as the air blast.

Detonation of a nuclear weapon in a forested area virtually guarantees fire damage at ranges greater than the range of air-blast damage. If the burst is in a city environment where buildings are closely spaced, say less than 10 to 15 meters, fires will spread from burning buildings to adjacent ones. In Germany and Japan in World War II, safe separation distance ranged from about 30 to 50 feet (for a 50 percent probability of spread), but for modern urban areas this distance could be larger. This type of damage is less likely to occur in suburban areas where buildings are more widely separated.



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