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Ionizing radiation is energetic Particles or Waves that have the potential to Ionize an Atom or Molecule through atomic interactions. It is a function of the energy of the individual particles or waves, and not a function of the number of particles or waves present. A large flood of particles or waves will not cause ionization if the individual particles or waves are not energetic enough. These ionizations, if enough occur, can be destructive to biological organisms, and can cause DNA Damage in individual cells. Extensive doses of ionizing radiation have been shown to have a Mutating effect to future generations of the individual receiving the dose. Examples of ionizing radiation are energetic Beta Particles , Neutrons , Alpha Particles and energetic Photon s (UV and above). The amount of energy required to ionize an atom or molecule may widely vary. X-ray s and Gamma Ray s will ionize almost any molecule or atom; Far Ultraviolet , near ultraviolet and Visible Light are ionizing to very few molecules; Microwave s and Radio Wave s are Non-ionizing Radiation . Visible Light is so ubiquitous that Molecules That Are Ionized By It will often react nearly spontaneously unless protected by materials that block the visible spectrum. Examples include photographic film and some molecules involved in Photosynthesis . Ionizing radiation has many practical uses in medicine, research, construction, etc. It also presents a health hazard to humans if used improperly. Both aspects are discussed below. TYPES OF RADIATION -4 nuclei and is stopped by a sheet of paper. Beta radiation, consisting of Electron s, is halted by an aluminium plate. Gamma radiation, consisting of energetic Photon s, is eventually absorbed as it penetrates a dense material.]] Ionizing radiation is produced by Radioactive Decay , Nuclear Fission and Nuclear Fusion , by extremely hot objects (the hot sun, e.g., produces ultraviolet), and by Particle Accelerator s that may produce, e.g., fast electrons or protons or Bremsstrahlung or Synchrotron Radiation . In order for radiation to be ionizing, the particles must both have a high enough energy and interact with the atom. Photons interact strongly with charged particles, so photons of sufficiently high energy are ionizing. The energy at which this begins to happen is in the Ultraviolet region; Sunburn is one of the effects of this ionization. Charged particles such as Electron s, Positron s, and Alpha Particle s also interact strongly with electrons. Neutron s, on the other hand, do not interact strongly with electrons, and so they cannot directly ionize atoms by this mechanism. However, fast neutrons will interact with the protons in hydrogen (in the manner of a billiard ball hitting another, sending it away with all of the first ball's energy of motion), and this mechanism produces proton radiation ( Fast Protons ). These are ionizing because of the strong interaction of the charged proton with the electrons in matter. Neutrons can also interact with atomic nuclei, depending on the nucleus and their velocity; these reactions happen with Fast Neutron s and Slow Neutron s, depending on the situation. Neutron interaction with nuclei in this manner often produces Radioactive nuclei, which produce ionizing radiation when they decay. In the picture at left, gamma quanta are represented by wavy lines, charged particles and neutrons by straight lines. The little circles show where ionization processes occur. An ionization event normally produces a positive atomic ion and an electron. High energy beta particles may produce Bremsstrahlung when passing through matter, or secondary electrons (δ-electrons); both can ionize in turn. Gamma quanta do not ionize all along their path like alpha or beta particles (see , Compton Effect , or Pair Production . By way of example, the figure shows Compton effect: two Compton scatterings that happen sequentially. In every scattering event, the gamma quantum transfers energy to an electron, and it continues on its path in a different direction with reduced energy. In the figure, the neutron collides with a proton of the material which then becomes a fast recoil proton that ionizes in turn. At the end of its path, the neutron is captured by some nucleus in an (n,γ)-reaction that leads to a Neutron Capture photon. The negatively charged electrons and positively charged Ion s created by ionizing radiation may cause damage in living tissue. If the dose is sufficient, the effect may be seen almost immediately, in the form of Radiation Poisoning . Lower doses may cause Cancer or other long-term problems. The effect of the very low doses encountered in normal circumstances (from both natural and artificial sources, like cosmic rays, medical X-rays and nuclear power plants) is a subject of current debate. A 2005 report released by the National Research Council (the BEIR VII report, summarized in {Link without Title} ) indicated that the overall cancer risk associated with background sources of radiation was relatively low. Radioactive materials usually release Alpha Particle s which are the nuclei of Helium , Beta Particle s, which are quickly moving Electron s or Positron s, or Gamma Ray s. Alpha and beta rays can often be shielded by a piece of Paper or a Sheet Of Aluminium , respectively. They cause most damage when they are emitted inside the human body. Gamma rays are less Ion izing than either alpha or beta rays, but protection against them requires thicker shielding. They produce damage similar to that caused by X-ray s such as burns, and Cancer through Mutation s. Human Biology resists Germline Mutation by either correcting the changes in the DNA or inducing Apoptosis in the mutated cell. Non-ionizing radiation is thought to be essentially harmless below the levels that cause heating. Ionizing radiation is dangerous in direct exposure, although the degree of danger is a subject of debate. Humans and animals can also be exposed to ionizing radiation internally: if radioactive isotopes are present in the environment, they may be taken into the body. For example, radioactive Iodine is treated as normal iodine by the body and used by the Thyroid ; its accumulation there often leads to thyroid Cancer . Some radioactive elements also Bioaccumulate . USES OF IONIZING RADIATION Ionizing radiation has many uses. An X-ray is ionizing radiation, and ionizing radiation can be used in medicine to kill cancerous cells. However, although ionizing radiation has many uses, the overuse of it can be hazardous to human health. Shop assistants in shoe shops used to use an X-ray machine to check a child's shoe size, but when it was discovered that ionizing radiation was dangerous these machines were promptly removed. Technical uses of ionizing radiation Since they are able to penetrate matter, ionizing radiations are used for a variety of measuring methods. ;Radiography by means of gamma or x rays :This is a method used in industrial production. The piece to be radiographed is placed between the source and a photographic film in a cassette. After a certain exposition time, the film is developed and it shows internal defects of the material if there are any. ;Gauges :Gauges use the exponential absorption law of gamma rays
;Applications using ionization of gases by radiation
Biological and medical applications of ionizing radiation In Biology , one uses mainly the fact that radiation Sterilizes , and that it enhances Mutation s. For example, mutations may be induced by radiation to produce new or improved species. A very promising field is the Sterile Insect Technique , where male insects are sterilized and liberated in the chosen field, so that they have no descendants, and the population is reduced. Radiation is also useful in sterilizing medical hardware or Food . The advantage for medical hardware is that the object may be sealed in plastic before sterilization. For food, there are strict regulations to prevent the occurrence of Induced Radioactivity . The growth of a seedling may be enhanced by radiation, but excessive radiation will hinder growth. Electrons, x rays, gamma rays or atomic Ion s may be used in Radiation Therapy to treat malignant tumors ( Cancer ). Tracer methods are used in Nuclear Medicine in a way analogous to the technical uses mentioned above. Natural background radiation Natural . Cosmic radiation The earth, and all living things on it, are constantly bombarded by radiation from outside our solar system of positively charged ions from Proton s to Iron Nuclei . The energy of this radiation can far exceed energies that humans can create even in the largest particle accelerators. This radiation interacts in the atmosphere to create secondary radiation that rains down, including X-rays , Muon s, protons, Alpha Particle s, Pion s, Electron s, and Neutron s. The Dose from cosmic radiation is largely from muons, neutrons, and electrons. The dose rate from cosmic radiation varies in different parts of the world based largely on the geomagnetic field, altitude, and solar cycle. The dose rate from cosmic radiation on aeroplanes is so high that, according to the United Nations UNSCEAR 2000 Report (see links at bottom), airline workers receive more dose on average than any other worker, including nuclear power plant workers. Solar radiation While most solar radiation is electromagnetic radiation, the sun also produces particle radiation, Solar Particles , which vary with the Solar Cycle . They are mostly Proton s; these are relatively low in energy (10-100 keV). The average composition is similar to that of the Sun itself. This represents significantly lower energy particles than come form cosmic rays. Solar particles vary widely in their intensity and spectrum, increasing in strength after some solar events such as Solar Flare s. Further, an increase in the intensity of solar cosmic rays is often followed by a ''decrease'' in the galactic cosmic rays, called a Forbush Decrease after their discoverer, the physicist Scott Forbush. These decreases are due to the Solar Wind which carries the sun's magnetic field out further to shield the earth more thoroughly from cosmic radiation. The ionizing component of solar radiation is negligible relative to other forms of radiation on Earth's surface. External terrestrial sources Most material on earth contains some radioactive atoms, if in small quantities. But most of terrestrial non-radon-dose one receives from these sources is from gamma-ray emitters in the walls and floors when inside the house or rocks and soil when outside. The major Radionuclide s of concern for terrestrial radiation are Potassium , Uranium and Thorium . Each of these sources has been decreasing in activity since the birth of the Earth so that our present dose from potassium-40 is about ½ what it would have been at the dawn of Life On Earth . Radon Radon -222 is produced by the decay of Radium -226 which is present wherever uranium is found. Since radon is a gas, it seeps out of uranium-containing soils found across most of the world and may concentrate in well-sealed homes. It is often the single largest contributor to an individual's background radiation dose and is certainly the most variable from location to location. Radon gas could be the second largest cause of lung cancer in America, after smoking. {Link without Title} Human-made radiation sources Natural and artificial radiation sources are identical in their nature and their effect. Above the background level of radiation exposure, the U.S. Nuclear Regulatory Commission (NRC) requires that its licensees limit human-made radiation exposure to individual members of the public to 100 Mrem (1 MSv ) per year, and limit occupational radiation exposure to adults working with radioactive material to 5,000 mrem (50 mSv) per year. The average exposure for Americans is about 360 mrem (3.6 mSv) per year, 81 percent of which comes from natural sources of radiation. The remaining 19 percent results from exposure to human-made radiation sources such as medical X-rays, most of which is deposited in people who have CAT Scans . This compares with the average dose received by people in the UK of about 2.2 mSv. One important source of natural radiation is Radon gas, which seeps continuously from bedrock but can, because of its high density, accumulate in poorly ventilated houses. The background rate varies considerably with location, being as low as 1.5 mSv/a in some areas and over 100 mSv/a in others. People in some areas of Ramsar , a city in northern Iran , receive an annual radiation absorbed dose from background radiation that is up to 260 mSv/a. Despite having lived for many generations in these high background areas, inhabitants of Ramsar show no significant cytogenetic differences compared to people in normal background areas; this has led to the suggestion that the body can sustain much higher steady levels of radiation than sudden bursts. Some human-made radiation sources affect the body through direct radiation, while others take the form of Radioactive Contamination and Irradiate the body from the inside. By far, the most significant source of human-made radiation exposure to the general public is from medical procedures, such as diagnostic X-ray s, Nuclear Medicine , and Radiation Therapy . Some of the major Radionuclide s used are I-131 , Tc-99 , Co-60 , Ir-192 , Cs-137 . These are rarely released into the environment. In addition, members of the public are exposed to radiation from consumer products, such as Tobacco ( Polonium -210), building materials, combustible fuels (gas, Coal , etc.), ophthalmic Glass , Television s, luminous Watch es and dials ( Tritium ), airport X-ray systems, Smoke Detector s ( Americium ), road construction materials, electron tubes, Fluorescent Lamp starters, Lantern mantles ( Thorium ), etc. Of lesser magnitude, members of the public are exposed to radiation from the Nuclear Fuel cycle, which includes the entire sequence from mining and milling of Uranium to the disposal of the spent fuel. The effects of such exposure have not been reliably measured. Estimates of exposure are low enough that proponents of nuclear power liken them to the mutagenic power of wearing trousers for two extra minutes per year (because heat causes mutation). Opponents use a cancer per dose model to prove that such activities cause several hundred cases of cancer per year. In a Nuclear War , Gamma Ray s from Fallout of Nuclear Weapon s would probably cause the largest number of casualties. Immediately downwind of targets, doses would exceed 300 Gy per hour. As a reference, 4.5 Gy (around 15,000 times the average annual background rate) is fatal to half of a normal population. Occupationally exposed individuals are exposed according to the sources with which they work. The radiation exposure of these individuals is carefully monitored with the use of pocket-pen-sized instruments called Dosimeter s. Some of the radionuclides of concern include Cobalt -60, Caesium -137, Americium -241 and Iodine -131. Examples of industries where occupational exposure is a concern include:
BIOLOGICAL EFFECTS OF IONIZING RADIATION The biological effects of radiation are thought of in terms of their effect on living Cells . For low levels of radiation exposure, the biological effects are so small they may not be detected in epidemiological studies. The body repairs many types of radiation and chemical damage. Biological effects of radiation on living cells may result in a variety of outcomes, including: #Cells experience DNA damage and are able to detect and repair the damage. #Cells experience DNA damage and are unable to repair the damage. These cells may go through the process of programmed cell death, or Apoptosis , thus eliminating the potential genetic damage from the larger tissue. #Cells experience a nonlethal DNA mutation that is passed on to subsequent cell divisions. This mutation may contribute to the formation of a cancer. Other observations at the tissue level are more complicated. These include: #In some cases, a small radiation dose reduces the impact of a subsequent, larger radiation dose. This has been termed an 'adaptive response' and is related to hypothetical mechanisms of Hormesis . Hormesis See Also: Radiation hormesis |
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