Ionizing radiation is used in medicine for both imaging and therapeutics. When a radioactive isotope decays, a particles (two protons and two neutrons) or b particles (electrons) may be released. In addition, g radiation may be emitted. X-rays, like g-rays, are high-frequency electromagnetic radiation; however, they are produced differently, being emitted when a beam of electrons is accelerated from a cathode to strike an anode, which is usually made of tungsten. The energy from these sources of ionizing radiation is initially dissipated in tissues by the displacement of electrons, thus producing chemically reactive ions. Therefore they may all cause tissue damage and chromosome changes, particularly in dividing cells. Exposure to all forms of radiation should be kept to a minimum.
Distance from the source is the most important factor. Alpha particles can only travel a few centimeters in air, and so the only precautions involve containment and the avoidance of ingestion or inhalation. Beta particles can be shielded by Perspex, which decelerates the particles slowly, thus preventing release of their energy as X-rays. A lead containment of thickness 7 cm will absorb 90 per cent of g-rays, and much less is needed for protection against X-rays.
Scintillation counters can be used to monitor levels of g irradiation. In units where high doses of X-ray exposure may be encountered, individuals need to wear photographic film badges to record the total dose absorbed.
Non-ionizing radiation from the lower-frequency range of the electromagnetic spectrum includes ultraviolet (UV) light (wavelength, 10-400 nm). Wavelengths below 200 nm do not pose a hazard as they are absorbed by air, and atmospheric ozone provides protection from wavelengths below 290 nm. Wavelengths of 280 to 320 nm (UV-B) have been associated with skin cancer (these effects are enhanced by UV-A which has wavelengths of 320-400 nm). Although minimal levels are observed from fluorescent lighting or from units where UV is used to limit bacterial contamination, care must be taken in neonatal units where such lights are used in the treatment of jaundice.
There is no evidence that video display unit operators are exposed to electric, magnetic, or radiation levels significantly above ambient levels. Clip-on UV screens are available and may reduce exposure. There is no conclusive evidence of increased eyesight deficits, epilepsy, or facial dermatitis. However, such equipment should be well positioned to avoid muscloskeletal injury.
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