The Effects of Nuclear War
Chapter 2
GENERAL DESCRIPTION OF EFFECTS
Fallout
While any nuclear explosion in the atmosphere produces some fallout, the fallout is far greater if the burst is on the surface, or at least low enough for the fireball to touch the ground. As chapter V shows in some detail, the fallout from air bursts alone poses long-term health hazards, but they are trivial compared to the other consequences of a nuclear attack. The significant hazards come from particles scooped up from the ground and irradiated by the nuclear explosion.
The radioactive particles that rise only a short distance (those in the “stem” of the familiar mushroom cloud) will fall back to earth within a matter of minutes, landing close to the center of the explosion. Such particles are unlikely to cause many deaths, because they will fall in areas where most people have already been killed. However, the radioactivity will complicate efforts at rescue or eventual reconstruction.
The radioactive particles that rise higher will be carried some distance by the wind before returning to Earth, and hence the area and intensity of the fallout is strongly influenced by local weather conditions. Much of the material is simply blown downwind in a long plume./p>
The map shown in figure 2 illustrates the plume expected from a 1-Mt surface burst in Detroit if winds were blowing toward Canada. The illustrated plume assumed that the winds were blowing at a uniform speed of 15 mph [24 km] over the entire region, The plume would be longer and thinner if the winds were more intense and shorter and somewhat more broad if the winds were slower. If the winds were from a different direction, the plume would cover a different area. For example, a wind from the northwest would deposit enough fallout on Cleveland to inflict acute radiation sickness on those who did not evacuate or use effective fallout shelters (figure 3). Thus wind direction can make an enormous difference. Rainfall can also have a significant influence on the ways in which radiation from smaller weapons is deposited, since rain will carry contaminated particles to the ground. The areas receiving such contaminated rainfall would become “hot spots,” with greater radiation intensity than their surroundings, When the radiation intensity from fallout is great enough to pose an immediate threat to health, fallout will generally be visible as a thin layer of dust.
The amount of radiation produced by fallout materials will decrease with time as the radioactive materials “decay.” Each material decays at a different rate, Materials that decay rapidly give off intense radiation for a short period of time while long-lived materials radiate less intensely but for longer periods, Immediately after the fallout is deposited in regions surrounding the blast site, radiation intensities will be very high as the short-lived materials decay. These intense radiations will decrease relatively quickly. The intensity will have fallen by a factor of 10 after 7 hours, a factor of 100 after 49 hours and a factor of 1,000 after 2 weeks. The areas in the plume illustrated in figures 2 and 3 would become “safe” (by peacetime standards) in 2 to 3 years for the outer ellipse, and in 10 years or so for the inner ellipse.
Some radioactive particles will be thrust into the stratosphere, and may not return to Earth for some years. In this case only the particularly long-lived particles pose a threat, and they are dispersed around the world over a range of latitudes, some fallout from U.S. and Soviet weapons tests in the 1950’s and early 1960’s can still be detected. There are also some particles in the immediate fallout (notably Strontium 90 and Cesium 137) that remain radioactive for years. Chapter V discusses the likely hazards from these long-lived particles.
The biological effects of fallout radiation are substantially the same as those from direct radiation, discussed above, people exposed to enough fallout radiation will die, and those exposed to lesser amounts may become ill. Chapter III discusses the theory of fallout sheltering, and Chapter IV some of the practical difficulties of escaping fallout from a large counterforce attack.
There is some public interest in the question of the consequences if a nuclear weapon destroyed a nuclear powerplant. The core of a power reactor contains large quantities of radioactive material, which tends to decay more slowly (and hence less intensely) than the fallout particles from a nuclear weapon explosion, Consequently, fallout from a destroyed nuclear reactor (whose destruction would, incidentally, require a high-accuracy surface burst) would not be much more intense (during the first day) or widespread than “ordinary” fallout, but would stay radioactive for a considerably longer time. Areas receiving such fallout would have to be evacuated or decontaminated; otherwise survivors would have to stay in shelters for months.