Radiation Effects on Humans This topic is also discussed in nuclear safety but because it is relevant, here is an overview as well. Certain body parts are more specifically affected by exposure to different types of radiation sources. Several factors are involved in determining the potential health effects of exposure to radiation. These include:
The most important factor is the amount of the dose - the amount of energy actually deposited in your body. The more energy absorbed by cells, the greater the biological damage. Health physicists refer to the amount of energy absorbed by the body as the radiation dose. The absorbed dose, the amount of energy absorbed per gram of body tissue, is usually measured in units called rads. Another unit of radation is the rem, or roentgen equivalent in man. To convert rads to rems, the number of rads is multiplied by a number that reflects the potential for damage caused by a type of radiation. For beta, gamma and X-ray radiation, this number is generally one. For some neutrons, protons, or alpha particles, the number is twenty. Hair The losing of hair quickly and in clumps occurs with radiation exposure at 200 rems or higher. Brain Since brain cells do not reproduce, they won't be damaged directly unless the exposure is 5,000 rems or greater. Like the heart, radiation kills nerve cells and small blood vessels, and can cause seizures and immediate death. Thyroid The certain body parts are more specifically affected by exposure to different types of radiation sources. The thyroid gland is susceptible to radioactive iodine. In sufficient amounts, radioactive iodine can destroy all or part of the thyroid. By taking potassium iodide can reduce the effects of exposure. Blood System When a person is exposed to around 100 rems, the blood's lymphocyte cell count will be reduced, leaving the victim more susceptible to infection. This is often refered to as mild radiation sickness. Early symptoms of radiation sickness mimic those of flu and may go unnoticed unless a blood count is done.According to data from Hiroshima and Nagaski, show that symptoms may persist for up to 10 years and may also have an increased long-term risk for leukemia and lymphoma. Intense exposure to radioactive material at 1,000 to 5,000 rems would do immediate damage to small blood vessels and probably cause heart failure and death directly. Gastrointestinal Tract Radiation damage to the intestinal tract lining will cause nausea, bloody vomiting and diarrhea. This is occurs when the victim's exposure is 200 rems or more. The radiation will begin to destroy the cells in the body that divide rapidly. These including blood, GI tract, reproductive and hair cells, and harms their DNA and RNA of surviving cells. Reproductive Tract Because reproductive tract cells divide rapidly, these areas of the body can be damaged at rem levels as low as 200. Long-term, some radiation sickness victims will become sterile.
Nuclear Radiation Effects on Equipment Many military systems (and, increasingly, civilian systems such as communications and weather satellites) must be capable of operating in environments containing sources of both natural and man-made radiation. In this context “radiation” refers to particle-like effects caused by neutrons, photons, and charged particles. When energetic radiation passes through matter, many complex processes occur including Compton scattering, photoelectric excitation, Auger electron emission, and pair production caused by photons; ionization caused by charged particles; and various nuclear processes caused by neutrons. Neutron-induced reactions can stimulate the release of charged particles and photons. As the level of integration of modern electronics increases, and as the size of individual devices on chips shrinks, electronic systems become increasingly vulnerable to any unwanted charge deposition or atomic displacement within the silicon base of the semiconductors. Effects which are generally short-lived are classed as transient radiation effects in electronics (TREE). EMP generated within the system by the passage of radiation through cases, circuit boards, components, and devices is called systems-generated EMP or SGEMP. The quantification of both phenomena is critical to the design of optical and electronic packages which can survive these effects. Ideally, such subsystems should be produced without significant increases in either cost or weight. Because the radiation which causes TREE and SGEMP is relatively strongly absorbed in the atmosphere, both phenomena are of primary importance to space systems exposed to high-altitude, high-yield nuclear detonations. Survivability analysis of semiconductor electronics requires quantitative understanding of at least the following:
These effects depend not merely on total dose but also on dose rate. Naturally occurring effects include total dose from electrons and protons trapped in the Van Allen belts and single-event upset (SEU) or even single-event burnout. SEU results when enough ionization charge is deposited by a high-energy particle (natural or man-produced) in a device to change the state of the circuit—for example, flipping a bit from zero to one. The effect on a power transistor can be so severe that the device burns out permanently. Large x- and gamma-ray dose rates can cause transient upset and permanent failure. These dose rates are delivered over a 10–100 ns time period. Delayed gammas in a 1–10 microsecond period at the same dose rate can cause latchup and burnout of devices. Latch up is the initiation of a high-current, low-voltage path within the integrated circuit and causes the circuit to malfunction or burnout by joule heating. Neutron fluences of greater than 10 n/cm 2 can cause permanent damage. A nuclear weapon will typically deliver this dose in a period from 0.1 to 10 ms. Total ionization greater than 5,000 rads in silicon delivered over seconds to minutes will degrade semiconductors for long periods. As device sizes decrease, the threshold for damage may go down. Nuclear radiation may increase risk of child leukemia Scientists found that young children living near nuclear power plants have a significantly higher risk of developing leukemia and other forms of cancer. Researchers found that 37 children within a 5-kilometer radius of nuclear power plants had developed leukemia between 1980 and 2003, while the statistical average during this time period was 17.An unnamed radiation protection expert familiar with the study said its conclusions understated the problem. He said the data showed there was an increased cancer risk for children living within 50 kilometers of a reactor. Nuclear radiation detection Micro mechanical sensors that can be coated with various interactive materials detect electromagnetic and nuclear radiation. As the micro mechanical sensors absorb radiation, the sensors bend and/or undergo a shift in resonance characteristics. The bending and resonance changes are detected with high sensitivity by any of several detection methods including optical, capacitive, and piezoresistive methods. Wide bands of the electromagnetic spectrum can be imaged with Pico Joule sensitivity, and specific absorptive coatings can be used for selective sensitivity in specific wavelength bands. Micro cantilevers coated with optical cross-linking polymers are useful as integrating optical radiation dosimeters. Nuclear radiation dosimetry is possible by fabricating cantilevers from materials that are sensitive to various nuclear particles or radiation. Upon exposure to radiation, the cantilever bends due to stress and its resonance frequency shifts due to changes in elastic properties, based on cantilever shape and properties of the coating. Equipments to Detect Nuclear Radiation Geiger Counter Most people have heard of a "Geiger Counter" for measuring radioactivity. This is actually a Geiger-Muller tube with some form of counter attached, which usually tells us the number of particles detected per minute ("counts per minute"). GM tubes work using the ionizing effect of radioactivity. This means that they are best at detecting alpha particles, because a-particles ionise strongly. Different models of GM tubes are available for detecting a, b and g radiation. Photographic Film Uranium compounds would darken a photographic plate, even if the plate were wrapped up so that no light could get in. Radioactivity will darken ("fog") photographic film, and we can use this effect to measure how much radiation has struck the film. Workers in the nuclear industry wear "film badges" which are sent to a laboratory to be developed, just like your photographs. This allows us to measure the dose that each worker has received (usually each month). The badges have "windows" made of different materials, so that we can see how much of the radiation was a particles, or b particles, or g rays. The Gold Leaf Electroscope Dry air is normally a good insulator, thus a charged electroscope will stay that way, as the charge cannot escape. When an electroscope is charged, the gold leaf sticks out, because the charges on the gold repel the charges on the metal stalk. When a radioactive source comes near, the air is ionised, and starts to conduct electricity. This means that the charge can "leak" away, the electroscope discharges and the gold leaf falls. The Spark Counter An early form of detector, the Spark Counter is another instrument that uses the ionising effect of radioactivity, and for this reason it works best with a particles. A high voltage is applied between the gauze and the wire, and adjusted until it is just below the voltage required to produce sparks. When a radioactive source is brought near, the air between the gauze and the wire is ionised, and sparks jump where particles pass. The Cloud Chamber There are two types of cloud chamber: the "expansion" type and the "diffusion" type. In both types, a or b particles leave trails in the vapour in the chamber, rather like high-altitude aircraft leave trails in the sky. The chamber contains a supersaturated vapour (e.g. methylated spirits), which condenses into droplets when disturbed and ionised by the passage of a particle (alpha particles are best for this). You can clearly see the direction and energy of the particles (low energy particles only leave short trails). Occasionally, a particle collides with an air molecule and changes direction. Expansion cloud chambers use a vacuum pump to briefly produce the right conditions for trails to form, whilst the Diffusion type uses solid Carbon Dioxide to cool the bottom of the chamber and produce a temperature gradient in which trails can be seen. The Bubble Chamber A similar idea to an expansion cloud chamber, particles leave trails of tiny bubbles in a liquid. This used to be the main instrument for tracking the results of collisions in particle accelerators. Powerful magnets would surround the chamber, so any charged particles passing though the chamber would move in curved paths. The shapes of the curves tell us about the charge, mass and speed of each particle, so we can work out what they are - otherwise one line of bubbles looks pretty much like another. Modern Detectors Scintillation Detectors work by the radiation striking a suitable material (such as Sodium Iodide), and producing a tiny flash of light. This is amplified by a "photomultiplier tube" which results in a burst of electrons large enough to be detected. Scintillation detectors form the basis of the hand-held instruments used to monitor contamination in nuclear power stations. They can recognise the difference between a, b and g radiation, and make different noises (such as bleeps or clicks) accordingly. Solid-State Detectors are the most up-to-date instruments. They are used in particle-accelerator laboratories to show the results of high-energy collisions, with banks of them clustered around the collision site, feeding data into huge computers. Dangers of nuclear radiation The main danger from radioactivity is the damage it does to the cells in your body. Most of this damage is due to ionization when the radiation passes, although if levels of radiation are high there can be damage due to heating effects as your body absorbs the energy from the radiation, rather like heating food in a microwave oven. This is particularly true of gamma rays. Alpha Particles Alpha particles are slow, have a short range in air, and can be stopped by a sheet of paper. You might therefore assume that alpha particles are the least dangerous of the three types of radiation. But it is wrong. They cannot penetrate your skin; you could easily eat or drink something contaminated with and a source. This would put a source of particles inside your body, wreaking havoc by ionising atoms in nearby cells. If this happens to part of the DNA in one of your cells, then that cell's instructions about how to live and grow have been scrambled. The cell is then likely to do something very different to what it's supposed to do, for example, it may turn cancerous and start multiplying uncontrollably.Thus alpha particles, whilst they have a low penetrating power, can be the most dangerous because they ionise so strongly. Beta particles Beta particles are more penetrating than alpha particles. They therefore cause less localized damage. However they are still very dangerous. An outside the body source of beta particles would be able to penetrate the skin and a source inside the body would be able to penetrate about 1mm into tissue. All nuclear radiation carries the risk of causing mutations to DNA or tumours. In high doses there is an increased risk of cell death. Gamma Rays Gamma rays hardly ionise atoms at all, so they do not cause damage directly in this way. However, gamma rays are very difficult to stop, you require lead or concrete shielding to keep you safe from them. When they are absorbed by an atom, those atom gains quite a bit of energy And may then emit other particles. If that atom is in one of your cells, this is not good! Positrons Positrons do not penetrate through matter very far at all before they disintegrate on meeting up with a matter counterpart. They therefore cause very localized ionisation. However each positron only causes a single ionisation so the damage it causes is very small in comparison to that an alpha particle causes. The gamma rays that result from the annihilation is very penetrating therefore they do not contribute to massive localized damage either. They are therefore safe to use in medical scanning (PET scanning). All nuclear radiation carries the risk of causing mutations to DNA or tumours. In high doses there is an increased risk of cell death. |
