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Ionising Radiation Protection
Radiation protection, sometimes known as radiological protection, is the science of protecting people and the environment from the harmful effects of both particle radiationand 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 main 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 doseproportionally.
- 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 sulfateand 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).
Practical radiation protection tends to be a job of juggling the three factors to identify the most cost effectivesolution.
In some cases, improper shielding can actually make the situation worse, when the radiation interacts with the shielding material and creates secondary radiationthat absorbs in the organisms more readily.
Different types of radiationbehave in a different way, so different shielding techniques are being used.
- Particle radiationconsists 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(heliumnuclei) is the easiest to shield, because the very massive alpha particlescan be stopped even with a leaf of paper.
- Beta radiation(electrons) is more difficult, but still a relatively thin layer of aluminumcan usually do the job. However, in cases where high energy beta particles are emitted (e.g. 32P), the Bremsstrahlungproduced 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[1].
- In case of Beta+ radiation (positrons) the gamma radiation from the annihilation reaction poses additional concern.
- Neutron radiationis not as readily absorbed as charged particle radiation. Neutrons are absorbed by nucleiof atoms in a nuclear reaction(which often leads to emission of gamma photons, causing additional shielding concerns), but fast neutronshave first to be slowed down (moderated) to slower speeds, by inelastic collisionswith heavy nuclei or by elastic collisionswith light ones. Large mass of hydrogen-rich material, eg. water(or concrete, which contain a lot of chemically-bound water), polyethylene, or paraffin waxis commonly used. It can be further combined with boronfor more efficient absorption of the thermal neutrons.
- Cosmic radiationis not a common concern, as the Earth's atmosphereabsorbs it and the magnetosphereacts as a shield, but it poses a problem for satellitesand 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 superconductorelectromagnets.[2][3]Aircrewsand frequent flyers are at a slight risk too.
- Electromagnetic radiationconsists of emissions of electromagnetic waves, the properties of which depend on the wavelength.
- X-rayand gamma radiationare best absorbed by atomswith heavy nuclei; the heavier the nucleus, the better the absorption. In some special applications, depleted uraniumis used, but leadis much more common. Barium sulfateis 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 shelteris 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,
- 150 m (500 ft) of air.
- Ultraviolet radiationis 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 layerabsorbs UV radiation, but its depletionconsiderably lowers its effectivity especially in northern and southern areas of the globe.
See also
- ALARA
- Fallout shelter
- List of nuclear accidents
External links
- Oregon Institute of Science and MedicineThis 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.de:Strahlenschutz
es:Protección radiológica
fr:Radioprotection
pl:Ochrona radiologiczna
This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Ionising+Radiation+Protection Wikipedia article Ionising Radiation Protection.
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