When a nuclear detonation occurs close to the ground surface, soil mixes with the highly radioactive fission products from the weapon. The debris is carried by the wind and falls back to Earth over a period of minutes to hours.
Essay on Radiation: Types, Effects and Protection | Environment
By contrast, the radiation dose from fallout is delivered over an extended period, as described in Chapter 5. Most of the dose from fallout is due to external exposure to gamma radiation from radionuclides deposited on the ground, and this is the only exposure pathway considered by the computer models that the Defense Threat Reduction Agency DTRA and Lawrence Livermore National Laboratory LLNL used to estimate health effects for this study. Below is a discussion of the possible. 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 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. 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. 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. 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.
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.
Examples of Radiation
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. The largest fraction of the risk is due to thyroid disease. Thermal radiation may make fire a collateral effect of the use of surface burst, airburst, or shallow-penetrating nuclear weapons.
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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, to 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.
Once started, fire spread continues until the fire runs out of fuel or until the distance to the next source of fuel is too great. Thus, fire caused directly by thermal ignitions, fire caused indirectly by disruptive blast waves, and spread of fire are all potential, but uncertain, effects. The area over which casualties would occur as a result of the various weapon effects outlined above depends primarily on the explosive yield of the weapon and the height or depth of the burst.
The areas affected by initial nuclear radiation and fallout also depend on the design of the weapon in particular, the fraction of the yield that is derived from fission reactions , and, in the case of fallout, on weather conditions during and after the explosion notably wind speed and direction, atmospheric stability, precipitation, and so on , terrain, and geology in the area of the explosion.
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The following calculations assume that the entire population is static and in the open. As an illustrative example, 7 Figure 6. As discussed in Chapter 5 , both of these weapons would produce a ground shock of about 1 kilobar at a depth of 70 meters. Figure 6.
Under these conditions and assumptions, the 10 kiloton EPW is estimated to result in about , casualties, compared with , casualties for the. Thus, in this example the use of an EPW would reduce casualties by about a factor of eight compared with a surface burst with equal destructive capacity against a buried target. Fallout is responsible for about 75 percent of the casualties from the 10 kiloton explosion compared with about 60 percent of the casualties from the kiloton explosion.
The hazard to people entering the area after the explosion in these scenarios would be due largely to external gamma radiation from fallout. This hazard decreases rapidly with time: the dose rate after 1 week is 10 times less than the dose rate 1 day after the explosion, and after 2 months it is reduced by an additional factor of Figures 6. Depending on the risk that is judged acceptable by commanders,. For example, a soldier entering the 10 millisieverts per hour 1, millirems per hour contour 1 day after the explosion would accumulate a total dose of about 0.
Army guidance for situations in which troops might receive as much as 0.
Fear of radiation is more dangerous than radiation itself
The estimates shown in Figures 6. The number of civilian casualties that would result from an attack depends on many variables, including the following: the distribution of the population around the point of detonation and the degree of sheltering that they have against blast, thermal, and radiation effects; weapon yield and design; height or depth of burst; and weather conditions during and after the explosion. As shown below, the estimated number of casualties ranges over four orders of magnitude—from hundreds to over a million—depending on the combination of assumptions used.
To explore in a parametric way the range of possibilities, the committee selected three notional targets:. Target A: an underground command-and-control facility in a densely populated area 3 kilometers from the center of a city with a population of about 3 million;. Target B: an underground chemical warfare facility 60 kilometers from the nearest city and 13 kilometers from a small town; and.
Target C: a large, underground nuclear weapons storage facility 20 kilometers from a small town. In each case, the committee asked DTRA to estimate the mean number of casualties deaths and serious injuries from prompt effects, and acute effects of fallout from external gamma radiation resulting from attacks with earth-penetrating weapons with yields ranging from 1 kiloton to 1 megaton, for populations completely in the open and completely indoors.
The means are averages over annual wind patterns, but they ignore precipitation. DTRA also estimated the mean number of casualties resulting from surface bursts with yields from 25 kilotons to 7. For selected cases, the committee asked the Lawrence Livermore National Laboratory to estimate the number of deaths from prompt effects and fallout, and to quantify the variability in acute and latent deaths from fallout owing to wind patterns.
For Figures 6. Note that for a given yield there is little or no difference between the effects of surface bursts and the EPWs. The curves for Targets B and C are steeper a. The number of casualties is similar for surface bursts of the same yield.
The Radiation And Its Health Effects
Note that for yields of less than kilotons, fallout is responsible for more casualties than are prompt effects. This is particularly true for Targets B and C, for which fallout is the only effect of low-yield explosions that can reach population centers. It is always useful to compare model predictions against relevant experience.
Fortunately, the relevant experience is very limited. In the case of the 15 kiloton device detonated over Hiroshima, an estimated 68, persons died and 76, persons were injured out of a total population of , For the 21 kiloton device detonated over Nagasaki, it is estimated that 38, persons died and 21, persons were injured out of a total population of , The Hiroshima and Nagasaki weapons were detonated at a fallout-free height of about meters and therefore produced no local fallout.
As mentioned, the results shown in Figures 6. Assuming that the entire population remains indoors and is thereby shielded from radiation reduces mean total casualties by a factor of up to 4 for Target A, and by a factor of 2 to 8 for Targets B and C. Not accounted for are post attack movement or evacuation of the population, but it is unlikely that individuals could, by fleeing the area of an attack, reduce their exposure to fallout significantly more than by remaining indoors.
Indeed, some people might greatly increase their exposure to fallout if they were to move through highly contaminated areas, as might occur if a major road out of the city were directly under the path of the cloud. Thus, in a population that has received no warning of an attack, the actual effects of sheltering and evacuation are likely to lie between the two extremes for a population that is assumed to be entirely indoors and one that is assumed to be entirely outdoors.
The use of an EPW instead of a surface-burst weapon generally will result in fewer casualties, because the yield of the EPW can be 15 to 25 times smaller than the yield of a surface-burst weapon for a given level of damage against a hard and deeply buried target HDBT. For Target A, casualties are reduced by a factor of 7 at low yields appropriate for target depths of less than meters and by a factor of 2 at high yields and deeper targets. For Target B, casualties are reduced by a factor of 10 to 30, and for Target C, by a factor of 15 to 60, depending on the yield and assumptions about shielding.
In general, the reduction factor is larger for targets in rural or remote areas. The DTRA results presented above do not include latent cancer deaths from fallout.