Long term radiation exposure results from residing in a fallout contaminated area for an extended period (external exposure), consuming food produced in a contaminated area (internal exposure), or both. We encourage you to read our updated PRIVACY POLICY and COOKIE POLICY. Sr-89 is an important hazard for a year or two after an explosion, but Sr-90 remains a hazard for centuries. These reactive chemical species then damage DNA and disrupt cellular chemistry in other ways - producing immediate effects on active metabolic and replication processes, and long-term effects by latent damage to the genetic structure. There are also risk coefficient for specific tissue exposures. These radicals are produced when the energetic radiation strikes a molecule in the living issue, and breaks it into ionized (electrically charged) fragments. Read Our Story. In general, higher total doses are required to produce a given level of acute sickness for longer exposure times. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories:[1]. Fallout is a complex mixture of different radioactive isotopes, the composition of which continually changes as each isotope decays into other isotopes. I will discuss such combined effects wherever appropriate. [37] As a result of numerous inelastic collisions, part of the kinetic energy of the fission fragments is converted into internal and radiation energy. Semiconductors, especially integrated circuits, are extremely susceptible to the effects of EMP due to the close proximity of the PN junctions, but this is not the case with thermionic tubes (or valves) which are relatively immune to EMP. This occurs only with tinder-like, or dark, easily flammable materials: dry leaves, grass, old newspaper, thin dark flammable fabrics, tar paper, etc. This makes cataract risk the most important tissue dose criterion for establishing safety standards. At the limit of the range for 3rd degree burns, the time lapse between suffering burns and being hit by the blast wave varies from a few seconds for low kiloton explosions to a minute of so for high megaton yields. When thermal radiation strikes an object, part will be reflected, part transmitted, and the rest absorbed. Contamination of 2 curies of Sr-90 per km^2 is the U.S. limit for food cultivation. When exposure occurred during the first trimester a significant increase in mentally impaired children were noted. Iodine-131 typically enters the body through the consumption of contaminated milk, which in turn results from milk cows consuming contaminated fodder. For example there is a 50% chance of permanent female sterility if ovaries are exposed to 200 rems, but this internal exposure is only encountered with whole body doses of 400-600 rems. Thus a 1000 rem lifetime whole body radiation exposure would bring about a 80% chance of contracting fatal cancer, in addition to the normal incidence of cancer (about 20%). Large doses of potassium iodide saturate the body with iodine and prevent any subsequent retention of radioiodine that is consumed. Sufficient tissue remains intact however to regenerate and heal the burned area quickly, usually without scarring. Convulsions occur which may be controlled with sedation. This causes vaporization of the surrounding material, resulting in its rapid expansion. [35] The second reason for this cluster bomb, or ‘layering’[36] (using repeated hits by accurate low yield weapons), is that this tactic along with limiting the risk of failure, also reduces individual bomb yields, and therefore reduces the possibility of any serious collateral damage to non-targeted nearby civilian areas, including that of neighboring countries. The shock wave initially moves at some 30 km/sec, a hundred times the speed of sound in normal air. Since the latent effects of radiation exposure are cumulative, and there does not appear to be any threshold exposure below which no risk is incurred, radiation safety standards have been set to minimize radiation exposure over time. 35:38. The scaling laws that were used to produce the table below, assume among other things, a perfectly level target area, no attenuating effects from urban terrain masking, e.g. Some rough guidelines are that by 300 milliseconds for a 20 kt bomb (1.8 seconds for a 1 Mt) 50% of the total thermal radiation has been emitted, and the rate has dropped to 40% of the second peak. The blast wind at sea level may exceed one thousand km/h, or ~300 m/s, approaching the speed of sound in air.