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The radiation dosimeter is of fundamental importance in the disciplines of radiation dosimetry and health physics. Other types of dosimeters are sound dosimeters, ultraviolet dosimeters and electromagnetic field dosimeters.
Ionizing radiation, such as X-rays, alpha rays, beta rays, and gamma rays, are undetectable by the human senses, therefore a measuring device is used to detect, measure and record these, and in some cases give an alarm when a preset level is exceeded.
Ionising radiation damage to the human body is cumulative, and is related to the total dose received, for which the SI unit is the sievert. Therefore, workers exposed to radiation, such as radiographers, nuclear power plant workers, doctors using radiotherapy, those in laboratories using radionuclides, and some HAZMAT teams are required to wear dosimeters so their employers can keep a record of their exposure to verify that it is below legally prescribed limits. Such devices are known as "legal dosimeters", meaning that they have been approved for use in recording personnel dose for regulatory purposes.
Crew members aboard NASA Space Shuttle missions had access to four types of active dosimeters should a radiation contingency occur. Crew members were required to wear passive dosimeters at all times throughout the mission.
Common types of wearable dosimeters for ionizing radiation include:
Quartz fiber dosimeters have to be prepared, usually daily, with a high voltage positive charge. As the gas in the dosimeter chamber becomes ionized by nuclear radiation the charge leaks away, causing the fiber indicator to rise up the graduated scale.
Film badge dosimeters are for one-time use only. The level of radiation absorption is indicated by a change to the film emulsion, which is shown when the film is developed.
Both the quartz and film badge types are being superseded by the TLD and Electronic Personal Dosimeter. The latter has a number of sophisticated functions such as alarming at preset levels and live readout of dose accumulated.
Manufacturing processes that treat products with ionizing radiation, such as food irradiation, use dosimeters to calibrate doses. These are different from personal dosimeters because they usually must have a greater range. They often consist of small blocks of material such as perspex (acrylic).
The dosimetry of neutron radiation uses specialised devices, such as superheated drop detectors.
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