Ionising radiation protection
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Radiation protection, sometimes known as radiological protection, is the science of protecting people and the environment from the harmful effects of both particle radiation and ionizing radiation.
It includes occupational radiation protection, which is the protection of workpeople; medical radiation protection, which is the protection of patients; and public radiation protection, which is about protection of individual members of the public, and of the population as a whole.
There are mainly three principles to radiation protection: those of time, distance and shielding. Radiation exposure can be managed by one or more of these:
- Reducing the time of an exposure reduces the effective dose proportionally.
- *An example of reducing radiation doses by reducing the time of exposures might be improving operator training to reduce the time they take to handle a source.
- Increasing distance reduces dose due to the inverse square law.
- *Distance can be as simple as handling a source with forceps rather than fingers.
- Adding shielding can also reduce radiation doses.
- *In x-ray facilities, the plaster on the rooms with the x-ray generator contains barium sulfate and the operators stay behind a leaded glass screen and wear lead aprons.
- *Almost any material can shield from gamma or x-rays in sufficient amounts (see below).
In some cases, improper shielding can actually make the situation worse, when the radiation interacts with the shielding material and creates secondary radiation that absorbs in the organisms more readily.
Different types of radiation behave in a different way, so different shielding techniques are being used.
- Particle radiation consists of a stream of charged or neutral particles, both charged ions and subatomic elementary particles. This includes solar wind, cosmic radiation, and neutron flux in nuclear reactors.
- * Alpha radiation (helium nuclei) is the easiest to shield, because the very massive alpha particles can be stopped even with a leaf of paper.
- * Beta radiation (electrons) is more difficult, but still a relatively thin layer of aluminum can usually do the job. However, in cases where high energy beta particles are emitted (e.g. 32P), the Bremsstrahlung produced by shielding this radiation with the normally used materials is itself dangerous; in such cases, shielding must be accomplished with low density materials, e.g. Plexiglas, acrylic, Lucite, plastic, wood, or water [link].
- * In case of Beta+ radiation (positrons) the gamma radiation from the annihilation reaction poses additional concern.
- * Neutron radiation is not as readily absorbed as charged particle radiation. Neutrons are absorbed by nuclei of atoms in a nuclear reaction (which often leads to emission of gamma photons, causing additional shielding concerns), but fast neutrons have first to be slowed down (moderated) to slower speeds, by inelastic collisions with heavy nuclei or by elastic collisions with light ones. Large mass of hydrogen-rich material, eg. water (or concrete, which contain a lot of chemically-bound water), polyethylene, or paraffin wax is commonly used. It can be further combined with boron for more efficient absorption of the thermal neutrons.
- * Cosmic radiation is not a common concern, as the Earth's atmosphere absorbs it and the magnetosphere acts as a shield, but it poses a problem for satellites and astronauts. While satellite electronics can be radiation hardened, astronauts can't, so they have to be shielded. Because weight is a premium on space technology, methods alternative to absorption are being proposed, eg. shielding using superconductor electromagnets.[link][link] Aircrews and frequent flyers are at a slight risk too.
- Electromagnetic radiation consists of emissions of electromagnetic waves, the properties of which depend on the wavelength.
- * X-ray and gamma radiation are best absorbed by atoms with heavy nuclei; the heavier the nucleus, the better the absorption. In some special applications, depleted uranium is used, but lead is much more common. Barium sulfate is used in some applications too. When cheapness is important, almost any material can be used, but it must be far thicker. One standard design practice is to measure the halving thickness of a material, the thickness that reduces gamma or x-ray radiation by half. When multiple thicknesses are built, the shielding multiplies. For example, a practical shield in a fallout shelter is ten halving-thicknesses of packed dirt. This reduces gamma rays by a factor of 1/1024, which is 1/2 multiplied by itself ten times. This multiplies out to 90 cm (3 ft) of dirt. Shields that reduce gamma ray intensity by 50% (1/2) include (see Kearney, ref):
- **9 cm (3.6 inches) of packed dirt or
- **6 cm (2.4 inches) of concrete,
- **1 cm (0.4 inches) of lead,
- **0.2 cm (0.08 inches) of depleted uranium,
- **150 m (500 ft) of air.
- * Ultraviolet radiation is absorbed in organic molecules of certain structures, being the active ingredients of sunscreens. Anything that stops ordinary low-energetic radiation will do the job too. The ozone layer absorbs UV radiation, but its depletion considerably lowers its effectivity especially in northern and southern areas of the globe.
See also
External links
- [Oregon Institute of Science and Medicine]This website offers the entire online version of Nuclear War Survival Skills with full graphics and web navigation, created with the permission of the author Cresson Kearny. This manual has proven technical info on expedient fallout shelter, shelter habitation, and assorted shelter system needs that can be created from common household items. OISM also offers free downloads of other civil defense and shelter information as well.
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