Effects of Nuclear Explosions

Factors like terrain, weather, the point of explosion in relation to Earths surface, and the weapons yield determine the effects of a nuclear explosion. The three effects of nuclear explosions are the blast effect; the thermal effect; and the nuclear radiation effect. Blast and thermal effects are associated with both chemical explosions and nuclear explosions, but only nuclear explosions produce nuclear radiation. The relative strength of each type of effect produced by the explosion of a nuclear weapon in the atmosphere depends on the weapon's construction. On the average, the energy of such an explosion is 50 per cent blast, 35 per cent thermal, and 15 per cent nuclear radiation. Cumulative data from United States atmospheric explosions are given in the table titled Effects of Atmospheric Nuclear Explosions.

In the event of a large-scale nuclear war, the explosions produced by the detonation of hundreds or thousands of nuclear weapons would blast a large amount of soil into the air. The explosions would also start wide-spread fires that would send a large amount of smoke high into the atmosphere with the formation of a fireball formed due to cloud of dust and hot gases under high pressure. The gases begin to expand forming a blast wave, or a shock wave, which is like a wall of highly compressed air moving rapidly away from the fireball. The blast wave created by a 1-megaton explosion travels about 12 miles from ground zero in only 50 seconds; ground zero is the point on the ground that lies directly below the explosion. As the wave moves forward, it creates overpressure because a 1-megaton explosion produces an overpressure that can destroy all buildings within 1 mile of ground zero. Moderate to severe damage can also be caused by this overpressure, within 6 miles of ground zero which are accompanied by strong winds reaching speeds of 400 miles per hour at 2 miles from ground zero. This blast wave along with the wind probably would kill majority of people within 3 miles of ground zero and some people between 3 and 6 miles from ground zero. Several other people within 6 miles of ground zero would face injury as well. Some scientific studies indicate that such a war could result in a phenomenon commonly referred to as nuclear winter. According to the studies, the dust and smoke might block out the sun for weeks or months, causing temperatures at the earth's surface to fall well below normal. Reduced temperatures, together with the lack of sunlight, could kill much of the plant life that animals need for food.

The ultraviolet, visible, and infrared radiation given off by the fireball forms the thermal radiation. The ultraviolet radiation gets rapidly absorbed by the particles in the air, thus causing little harm. However, the visible infrared radiation causes eye injuries as well as skin burns called flash burns, which caused 20 to 30 per cent of the deaths at Hiroshima and Nagasaki.

Thermal radiations can also ignite newspapers and dry leaves, causing huge fires. Scientists are also of the opinion that the smoke from such fire absorbs so much sunlight that it lowers the surface temperature of the earth for several months or years which could result in crop failure and famine. However, these effects can vary considerably, depending on several conditions. In clean air it could even be only one-hundredth as strong as in fog.

A person can be protected from the flash burns of thermal radiation by walls, buildings, trees, and rocks. Light-colored clothing also reflects heat, and so can help protect a person. However, thermal radiation from a 1-megaton explosion can produce second-degree burns up to 11 miles from ground zero. As the thermal radiation last only about 10 seconds, it would not completely burn, but only char heavy fabrics and thick pieces of wood or plastic.

The nuclear radiation resulting from a nuclear explosion is divided into two categories: (1) initial, or prompt, radiation; and (2) residual, or fallout, radiation. Prompt radiation is radiation that is emitted within one minute of the explosion. All subsequent radiation is termed fallout radiation.

Prompt Radiation

consists primarily of gamma rays (radiant energy of the same nature as light but of much higher frequency) and neutrons, which are a form of radiation similar to X rays. Some of the gamma rays and neutrons are emitted immediately, and the rest come out as a massive mushroom-shaped cloud of radioactive material.

Effects of Atmospheric Nuclear Explosions
The data for blast damage are based on the explosion height that gives maximum blast effect, and the ranges are measured from ground zero, the point on the ground directly below the burst. Ranges for the last two columns are measured from the explosion center.
Range within which Stated Effects Will Occur
Blast EffectThermal EffectNuclear Radiation Effect
EXPLOSION YIELDDeath to 50 per cent of exposed persons Severe damage to wooden-frame structures Second-degree burns to all exposed persons; ignition of combustible materials Death to 50 per cent of exposed persons
1 kiloton 0.3 mi 0.5 km 0.6 mi 1.0 km 0.5 mi 0.8 km 0.5 mi 0.8 km
10 kilotons 0.8 1.3 1.4 2.3 1.4 2.3 0.8 1.3
100 kilotons 1.9 3.1 2.8 4.5 2.5 4.0 1.1 1.8
1 megaton 4.8 7.7 6.4 10.3 10.0 16.1 1.5 2.4
10 megatons 12.0 19.3 13.7 22.0 23.0 37.0 2.3 3.7

By destroying cells or parts of cells of the body, gamma rays and neutrons can cause severe illness; in large doses they render a person helpless and cause death within hours or days. The cells that carry the factors governing heredity are especially susceptible to radiation damage. Thus, a person may become sterile as the result of radiation, or the heredity factors may be so altered that children may be born with serious birth defects.

A neutron bomb is a low-yield fusion bomb that produces a proportionately large amount of prompt radiation (primarily in the form of neutrons). The bomb is designed as a tactical weapon; the prompt radiation would incapacitate or kill most soldiers within the limited area of a battlefield, yet there would be relatively little fallout or destruction of buildings or other property.

Fallout Radiation

comes from the radioactive atomic nuclei formed from the materials inside the bomb and the bomb casing. Residual nuclear radiation is given off later than one minute after the explosion. Residual radiation created by fission consists of gamma rays and beta particles or electrons. Residual radiation produced by fusion consists mainly of neutrons. It strikes rock, soil and water particles and other materials that make up the mushroom-shaped cloud. Thus, these particles become radioactive, fall back to earth and are known as fallout. The closer an explosion occurs to Earths surface, the more is the fallout produced. Fallout radiations are of two types: early fallout and delayed fallout. When a nuclear explosion occurs on or near the ground, most of the radioactive debris attaches itself to particles of dirt carried into the air and falls to earth within a few days, killing or severely injuring living things as it reaches the ground within 24 hours of the explosion with heavy and highly radioactive particles. This is called early fallout. Some of the radioactive debris rises high into the atmosphere and can remain aloft for months or years, causing long-term radiation damage to living things as it reaches the ground from 24 hours to many years after the explosion has taken place. It has tiny, invisible, particles that fall in small amounts over large areas. This is called delayed fallout.

The principal hazards from fallout are gamma radiation from local fallout (fallout that reaches the earth within 24 hours of the explosion) and radiation from strontium 90, a radioactive isotope of the element strontium.

Strontium 90 is one of the more than 200 different isotopes that are formed during the fissioning of uranium or plutonium. Strontium is chemically similar to the element calcium, which is a major constituent of bone. For this reason strontium 90 will become permanently fixed in the bones of growing children when taken internally (in dairy products or vegetables, for example). Strontium 90 gives off beta particles (electrons emitted from the nucleus), which can cause bone cancer and leukemia. It takes 28 years, on the average, for half of the strontium 90 assimilated to become stable, or nonradioactive.

The isotope cesium 137, which emits gamma rays, can also be assimilated internally. The amount of cesium 137 is carefully checked in fallout measurements, along with the amount of strontium 90. Cesium 137 passes from the body after a few months.

The casing of a so-called “clean” bomb contains little or no material that can be made radioactive. A “dirty” bomb, on the other hand, has a container composed of one or more metals that can be made to emit nuclear radiation. A thick casing of cobalt, for example, around a fusion bomb (a combination called a “cobalt bomb”) could result in the creation of huge quantities of radioactive cobalt 60 that theoretically could make large areas of the earth uninhabitable for years.

A properly designed fallout shelter, or even a modified basement in a home, will provide good protection against all airborne nuclear radiations. A fallout shelter offers no protection, however, against internally assimilated fallout, such as that contained in radioactive food and drink.