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Chapter Six

ALARA As low as reasonably achievable. Adopted as a culture and attitude of professionals who work with ionizing radiation to minimize radiation exposure and risks.
Collimation The restriction of the useful beam to an appropriate size. Intraoral beam diameter is collimated to 2 3/4 in. (7 cm) at the skin surface.
Half-Value Layer Thickness of a specified material that, when introduced into the path of a given beam of radiation, reduces the exposure rate by half.
Filtration The use of absorbers for selectively absorbing or screening out low-energy x-rays from the primary beam. See Added filtration, Inherent filtration, and Total filtration.
Total Filtration The combination of inherent and added filtration in an x-ray machine. Many states require a total filtration of 2.5 mm of aluminum equivalent for x-ray machines operating at or above 70 kVp.
Inherent Filtration Filtration built into the x-ray machine by the manufacturer. This includes the glass x-ray tube envelope, the insulating materials of the tube head, and the materials that seal the port.
Added Filtration Added to the inherent filtration built into the x-ray machine. In the form of thin disks, pure aluminum, which is inserted between the x-ray tube and lead collimator when the inherent filtration does not meet modern radiation safety requirements.
Lead Apron Protective barrier made of lead or lead-equivalent materials. Shields patients' gonadal areas from radiation during dental x-ray exposures.
Maximum Permissible Dose (MPD) The maximum accumulated dose that persons who are occupationally exposed may have at any given time of their life. Is not expected to cause detectable body damage. Currently established at 0.05 Sv per year (5 rem/year) whole body.
PID See Position indicating device.
Primary Beam The original undeflected useful beam of radiation that emanates at the focal spot of the x-ray tube and emerges through the aperture of the tube head.
Radiation Worker Professional who works with or around ionizing radiation or equipment that produces ionizing radiation.
Scatter Radiation Radiation that has been deflected from its path by impact during its passage through matter. This form of secondary radiation is scattered in all directions by the tissues of the patient's head.
Thermoluminescent Dosimeter (TLD) Monitoring device containing certain crystalline compounds (usually lithium fluoride) that store energy when struck by x-rays. When heated, the crystals give off light in proportion to the amount of radiation exposure.
Thyroid Collar An attached or detachable supplement to the lead apron. Contains 0.25 mm lead or lead-equivalent materials to protect the radiosensitive thyroid gland in the neck region during the exposure of intraoral radiographs.
Created by: daisenmurray