How does nuclear radiation after an atomic blast work?
I always believe that after a nuclear explosion that there is this nuclear fallout, but isn’t there a way to get rid of it? or is it going to be around for a long time. I remember hearing a weapons expert on talk radio say that U.S. Nuclear weapons now are more advanced to the point where during a nuclear explosion, all the radioactive materials burn up, thus almost reducing the Nuclear Fallout to none. Plus, I remember him saying that after a Nuclear blast, the way to get rid of the radiation is to get out a Geiger Counter with some protective gear and pick up all the radioactive materials left over. I mean how is Nagasaki and Hiroshima habitable now?
August 3rd, 2010 at 3:49 am
eventually the mount of radiation will dissipate on its own, giga counter will work but extremely slow. protection from fallout is a lead case and a closed air supply. it wont save you from the blast but it will help you after wards.
August 3rd, 2010 at 4:02 am
well, this a complicated one…
http://en.wikipedia.org/wiki/Nuclear_fallout
the reason hiroshima had so little deadly nuclear fallout is that the bomb was detinated 1000ft above the ground…. To destroy underground bunkers and chemical or biological agents, nuclear weapons must be detonated at or below the earth’s surface. Their radioactive products attach to bits of earth and rock, falling back to the ground within minutes or hours, before their radioactivity has had time to decay. For all their physical destructiveness, the nuclear weapons that exploded 1,000 feet over Hiroshima and Nagasaki produced little lingering fallout; people entering the cities immediately after the attacks were unharmed. In contrast, radioactive fallout from a Hiroshima-sized bomb detonated at ground level would kill civilians as far as 30 kilometers downwind; for our nine-megaton bomb, that distance would be increased more than tenfold. That bomb, if dropped in western Iraq, could contaminate cities as far away as Tel Aviv. American troops would have to avoid contaminated zones, complicating battlefield strategy and tactics.
When uranium-235 undergoes fission, the average of the fragment mass is about 118, but very few fragments near that average are found. It is much more probable to break up into unequal fragments, and the most probable fragment masses are around mass 95 and 137. Most of these fission fragments are highly unstable (radioactive), and some of them such as cesium-137 and strontium-90 are extremely dangerous when released to the environment.
Cesium-137 and strontium-90 are the most dangerous radioisotopes to the environment in terms of their long-term effects. Their intermediate half-lives of about 30 years suggests that they are not only highly radioactive but that they have a long enough halflife to be around for hundreds of years. Iodine-131 may give a higher initial dose, but its short halflife of 8 days ensures that it will soon be gone. Besides its persistence and high activity, cesium-137 has the further insidious property of being mistaken for potassium by living organisms and taken up as part of the fluid electrolytes. This means that it is passed on up the food chain and reconcentrated from the environment by that process.
August 3rd, 2010 at 4:35 am
A geiger counter is only a device for measuring alpha and beta particles,it wont get rid of the radiation,especially not at the level a nuclear blast produces. The level of radiation at New Mexico (where the first bomb was tested before Hiroshima) is still to this day 50 times higher than normal background radiation levels
August 3rd, 2010 at 5:34 am
Fallout is the residual radiation hazard from a nuclear explosion and is named from the fact that it “falls out” of the atmosphere into which it is spread during the explosion. It commonly refers to the radioactive dust created when a nuclear weapon explodes. This radioactive dust, consisting of hot particles, is a kind of radioactive contamination.Fallout can also refer to nuclear accidents, although a nuclear reactor cannot explode exactly like a nuclear weapon. It is important to note that the isotopic signature of bomb fallout is so very different to the fallout from a serious power reactor accident (such as Chernobyl). The key differences are due to volitility and half life.
Volitility
The boiling point of an element (or its compounds) is able to control the percentage of that elements which is released by a power reactor accident. In addition the ability of an element to form a solid controls the rate at which it is deposited on the ground after it has been injected into the atomsphere by a nuclear detonationThere will be large amounts of particles of less than 100 nm to several millimeters in diameter generated in a surface burst in addition to the very fine particles which contribute to worldwide fallout. The larger particles spill out of the stem and cascade down the outside of the fireball in a downdraft even while the cloud rises, so fallout begins to arrive near ground zero within an hour and more than half the total bomb debris is deposited on the ground within about 24 hours as local fallout.
It is important to note that the chemical properties of the different elements in the fall out will control the rate at which they are deposited on the ground. The more involitile elements will deposit first. T. Imanaka, S. Fukutani, M. Yamamoto, A. Sakaguchi and M. Hoshi, J. Radiation Research, 2006, 47, Suppl A121-A127 give a table of the degree of the relative tendancy of elements to form solids.
Per capita thyroid doses in the continental United States resulting from all exposure routes from all atmospheric nuclear tests conducted at the Nevada Test Site from 1951-1962.Severe local fallout contamination can extend far beyond the blast and thermal effects, particularly in the case of high yield surface detonations. The ground track of fallout from an explosion depends on the weather situation from the time of detonation onwards. In stronger winds, fallout travels faster but takes the same time to descend, so although it covers a larger path, it is more spread out or diluted. So the width of the fallout pattern for any given dose rate is reduced, where the downwind distance is increased by higher winds. The total amount of activity deposited up to any given time is the same irrespective of the wind pattern, so the overall casualty figures from fallout will generally be independent of the winds. But thunderstorms can bring down activity as rain more rapidly than dry fallout, particularly if the mushroom cloud is low enough to be below, or mixed with, the thunderstorm.
Whenever individuals remain in a radiologically contaminated area, such contamination will lead to an immediate external radiation exposure as well as a possible later internal hazard due to inhalation and ingestion of radiocontaminants, such as the rather short-lived iodine-131, which is accumulated in the thyroid.
Half life
In bomb fallout a large amount of short lived isotopes such as 97Zr are present, this isotope and the other shortlived isotopes are being constantly generated in a power reactor but because the criticality occurs over a long length of time the majority of these short lived isotopes decay before they can be released.
.A nuclear explosion vaporizes any material within the fireball, including the ground if it is nearby and this is combined with residual ionizing radiation to produce fallout. The sources of this residual ionizing radiation are:
Fission products. These are intermediate weight isotopes which are formed when a heavy uranium or plutonium nucleus is split in a fission reaction. There are over 300 different fission products that may result from a fission reaction. Many of these are radioactive with widely differing half-lives. Some are very short, that is, fractions of a second, while a few are long enough that the materials can be a hazard for months or years. Their principal mode of decay is by the emission of beta radiation, usually accompanied with gamma radiation. Approximately 60 g of fission products are formed per kiloton of yield. The estimated activity of this quantity of fission products 1 minute after detonation is 1.1 ZBq, equal to that of 30 Gg of radium, in equilibrium with its decay products. The mixture of fission product radioisotopes is very complex. Unfissioned nuclear material. Nuclear weapons are relatively inefficient in their use of fissionable material, usually only 2%-40% of the fissionable material undergoes fission and much of the uranium and plutonium is dispersed by the explosion without undergoing fission. Such unfissioned nuclear material decays by the emission of alpha particles and is of relatively minor importance.
Neutron-induced activity. If atomic nuclei capture neutrons when exposed to a flux of neutron radiation, they will, as a rule, become radioactive (neutron-induced activity) and then decay by emission of beta and gamma radiation over an extended period of time. Neutrons emitted as part of the initial nuclear radiation will cause activation of the weapon residues. In addition, atoms of environmental material, such as soil, air, and water, may be activated, depending on their composition and distance from the burst. For example, a small area around ground zero may become hazardous as a result of exposure of the minerals in the soil to initial neutron radiation. This is due principally to neutron capture by sodium (Na), manganese, aluminum, and silicon in the soil. This is a relatively negligible hazard because of the limited area involved.
Higher actinides are formed during a nuclear detonation. The neutron flux is very high so too little time exists between each neutron capture for beta decay. Hence a different group of isotopes is formed to those which are formed in a normal low flux power reactor (S-Process). This is an example of the R-Process which is also seen in exploding stars. These higher actinides are known as minor actinides in the context of used power reactor fuel. Some of the higher actindies were first found in the fall out from bomb tests, for instance einsteinium (element 99) was first found in the fallout from a hydrogen bomb test.There are many types of fallout, ranging from the global type to the more area-restricted types.
Worldwide fallout
After an air burst the fission products, unfissioned nuclear material, and weapon residues which have been vaporized by the heat of the fireball will condense into a fine suspension of very small particles 10 nm to 20 µm in diameter. These particles may be quickly drawn up into the stratosphere, particularly if the explosive yield exceeds 10 kt. They will then be dispersed by atmospheric winds and will gradually settle to the earth’s surface after weeks, months, and even years as worldwide fallout.
The radiobiological hazard of worldwide fallout is essentially a long-term one due to the potential accumulation of long-lived radioisotopes, such as strontium-90 and caesium-137, in the body as a result of ingestion of foods incorporating these radioactive materials. This hazard is much less serious than those which are associated with local fallout and, therefore, is not discussed at length here. Local fallout is of much greater immediate operational concern.
This type of fallout is featured in the novels On the Beach by British author Nevil Shute and Do Androids Dream of Electric Sheep? by Philip K. Dick.
Local fallout
The roughly 280 mile long fallout plume from 15 Mt shot Castle Bravo, ca. 1954In a land or water surface burst, large amounts of earth or water will be vaporized by the heat of the fireball and drawn up into the radioactive cloud. This material will become radioactive when it condenses, with fission products and other radiocontaminants that have become neutron-activated. For a good paper about the isotropic signature of the local bomb fallout from a ground burst see T. Imanaka, S. Fukutani, M. Yamamoto, A. Sakaguchi and M. Hoshi, J. Radiation Research, 2006, 47, Suppl A121-A127. Note that many of the isotopes in the table below will decay into the isotopes that many people are more familar with.There are two main considerations for the location of an explosion: height and surface composition. A nuclear weapon detonated in the air, called an air burst, will produce less fallout than a comparable explosion near the ground. This is due to the fact that less particulate matter will be contaminated and kicked up by the explosion. Detonations at the surface, surface bursts, will tend to produce more fallout material.
In case of water surface bursts, the particles tend to be rather lighter and smaller and so produce less local fallout but will extend over a greater area. The particles contain mostly sea salts with some water; these can have a cloud seeding effect causing local rainout and areas of high local fallout. Fallout from a seawater burst is unusually difficult to remove once it has soaked into porous surfaces, because the fission products are present as metallic ions which become chemically bonded to many surfaces. Water and detergent will not remove more than about 50% of this activity from concrete or steel, which will require sandblasting or acidic treatment. After the Crossroads underwater test it was found that wet fallout needs to be immediately removed from ships by continuous water washdown (such as from the fire sprinkler system on the decks).
For subsurface bursts, there is an additional phenomenon present called “base surge”. The base surge is a cloud that rolls outward from the bottom of the subsiding column, due to an excessive density of dust or water droplets in the air. For underwater bursts the visible surge is, in effect, a cloud of liquid (usually water) droplets with the property of flowing almost as if it were a homogeneous fluid. After the water evaporates, an invisible base surge of small radioactive particles may persist.
For subsurface land bursts, the surge is made up of small solid particles, but it still behaves like a fluid. A soil earth medium favors base surge formation in an underground burst. Although the base surge typically contains only about 10% of the total bomb debris in a subsurface burst, it can create larger radiation doses than fallout near the detonation, because it arrives sooner than fallout, before so much radioactive decay has occurred.
Meteorological
Comparison of fallout gamma dose and dose rate contours for a 1 Mt fission land surface burst, based on DELFIC calculations. Due to radioactive decay, the dose rate contours contract after fallout has arrived, but dose contours continue to growMeteorological conditions will greatly influence fallout, particularly local fallout. Atmospheric winds are able to bring fallout over large areas. For example, as a result of a Castle Bravo surface burst of a 15 Mt thermonuclear device at Bikini Atoll on March 1, 1954, a roughly cigar-shaped area of the Pacific extending over 500 km downwind and varying in width to a maximum of 100 km was severely contaminated. There are three very different versions of the fallout pattern from this test, because the fallout was only measured on a small number of widely spaced Pacific Atolls. The two alternative versions both ascribe the high radiation levels at north Rongelap to a downwind hotspot caused by the large amount of radioactivity carried on fallout particles of about 50-100 micrometres size [1].
After Bravo it was discovered that fallout landing on the ocean disperses in the top water layer (above the thermocline at 100 m depth), and the land equivalent dose rate can be calculated by multiplying the ocean dose rate at two days after burst by a factor of about 530. In other 1954 tests, including Yankee and Nectar, hotspots were mapped out by ships with submersible probes, and similar hotspots occurred in 1956 tests such as Zuni and Tewa [2] However, the major U.S. ‘DELFIC’ (Defence Land Fallout Interpretive Code) computer calculations use the natural size distributions of particles in soil instead of the afterwind sweep-up spectrum, and this results in more straightforward fallout patterns lacking the downwind hotspot. For civil defence purposes it is simpler.
Snow and rain, especially if they come from considerable heights, will accelerate local fallout. Under special meteorological conditions, such as a local rain shower that originates above the radio-active cloud, limited areas of heavy contamination just downwind of a nuclear blast may be formed.
Effects of fallout
A wide range of biological changes may follow the irradiation of animals. These vary from rapid death following high doses of penetrating whole-body radiation, to essentially normal lives for a variable period of time until the development of delayed radiation effects, in a portion of the exposed population, following low dose exposures.
The unit of actual exposure is the Roentgen which is defined in ionisations per unit volume of air, and all ionisation based instruments (including geiger counters and ionisation chambers) measure exposure. However, effects depend on the energy per unit mass not the exposure measured in air. A deposit of 1 joule per kilogram has the unit of 1 gray. For 1 MeV energy gamma rays, an exposure of 1 roentgen in air will produce a dose of about 0.01 gray, i.e., 1 centigray (cGy) in water or surface tissue. Because of shielding by the tissue surrounding the bones, the bone marrow will only receive about 0.67 cGy when the air exposure is 1 roentgen and the surface skin dose is 1 cGy. Some of the lower values reported for the amount of radiation which would kill 50% of personnel (the ‘LD50’) refer to bone marrow dose, which is only 67% of the air dose.
Short term
Median lethal dose (LD50): When comparing the effects of various types or circumstances, that dose which is lethal to 50% of a given population is a very useful parameter. The term is usually defined for a specific time, being limited, generally, to studies of acute lethality. The common time periods used are 30 days or less for most small laboratory animals and to 60 days for large animals and humans. It should be understood that the LD50 figure assumes that the individuals did not receive other injuries or medical treatment.
It was estimated some years ago that with the best possible medical care, the LD50 for gamma rays is 3.5 Gy, while under more dire conditions of war (a bad diet, little medical care, poor nursing) that the LD50 will be 2.5 Gy (250 rad).
At 1 hour after burst the radiation from fallout in the crater region is 30 grays per hour (Gy/h) for a surface burst. A cumulative dose of 3.5 Gy is fatal to half of a population of humans (it has been estimated that the LD50 dose under the conditions of nuclear war {poor diet, poor medical care etc} would be 2.5 Gy). There have been few documented cases of survival beyond 6 Gy. One person at Chernobyl survived a dose of more than 10 Gy, but many of the persons exposed there were not uniformly exposed over their entire body. If a person is exposed in a non-homogeneous manner then a given dose (averaged over the entire body) is less likely to be of a lethal dose. For instance if a person gets a hand/low arm dose of 100 Gy which gives them an overall dose of 4 Gy then they are more likely to survive than a person who gets a 4 Gy dose uniformly over their entire body. A hand dose of 10 Gy or more will likely result in loss of the hand; a British industrial radiographer who got a lifetime hand dose of 100 Gy lost his hand because of radiation dermatitis. Most people become ill after an exposure to 1 Gy or more. The fetuses of pregnant women are often more vulnerable than the host body and may miscarry, especially in the first trimester. Though the human biology resists mutation from large radiation exposure; grossly mutated fetuses usually miscarry, and this often causes gene-faults. Civilian dose rates in peacetime range from 30 to 100 µGy/a.
Fallout radiation falls off (‘decays’) exponentially relatively quickly with time. Most areas become fairly safe for travel and decontamination after three to five weeks.
The most dangerously known emissions from fallout are gamma rays, which travel in straight lines, like ordinary light. The fallout particles emit gamma rays in the same way that a light bulb emits light. Gamma rays cannot be seen, smelled, or felt. Special equipment is required to detect and measure gamma rays (Such as geiger counters, dosimeters).
For yields of up to 10 kt of TNT, prompt radiation is the dominant producer of casualties on the battlefield. Humans receiving an acute incapacitating dose (30 Gy) will have their performance degraded almost immediately and become ineffective within several hours. However, they will not die until 5 to 6 days after exposure assuming they do not receive any other injuries.
Individuals receiving less than a total of 1.5 Gy will not be incapacitated. Between those two extremes, people receiving doses greater than 1.5 Gy will become disabled; some will eventually die.
A dose of 5.3 Gy to 8.3 Gy is considered lethal but not immediately incapacitating. Personnel exposed to this amount of radiation will have their performance degraded within 2 to 3 hours, depending on how physically demanding the tasks they must perform are, and will remain in this disabled state at least 2 days. However, at that point they will experience a recovery period and be effective at performing non-demanding tasks for about 6 days, after which they will relapse for about 4 weeks. At this time they will begin exhibiting symptoms of radiation poisoning of sufficient severity to render them totally ineffective. Death follows at approximately 6 weeks after exposure, although results may vary.
Long term
Late or delayed effects of radiation occur following a wide range of doses and dose rates. Delayed effects may appear months to years after irradiation and include a wide variety of effects involving almost all tissues or organs. Some of the possible delayed consequences of radiation injury are life shortening, carcinogenesis, cataract formation, chronic radiodermatitis, decreased fertility, and genetic mutations.
Tactical military considerations
Comparison of predicted fallout “hotline” with test results in the 3.53 Mt 15% fission Zuni test at Bikini in 1956. The predictions were made under simulated tactical nuclear war conditions aboard ship by Edward A. Schuert.Blast injuries and thermal burns, due to the use of nuclear weapons for military action, in many cases will far outnumber radiation injuries. However, radiation effects are considerably more complex and varied than are blast or thermal effects and are subject to considerable misunderstanding.
The closer to ground an atomic bomb is detonated, the more dust and debris is thrown into the air, resulting in greater amounts of local fallout. From a tactical standpoint, this has the disadvantage of hindering any occupation/invading efforts until the fallout clears, but more directly, the impact with the ground severely limits the destructive force of the bomb. For these reasons, ground bursts are not usually considered tactically advantageous, with the exception of hardened underground targets such as missile silos or command centers. “Salting” enemy territory with a fallout-heavy atomic burst could be used to deny enemy access to a contaminated area but such use is generally not considered an ethical military action by critics.[citation needed]
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