Dosimeter

Fiber dosimeter (see gallery below for view through dosimeter)

Dosimeters measure an individual's or an object's exposure to something in the environment — particularly to a hazard inflicting cumulative impact over long periods of time, or over a lifetime. This article concentrates on the radiation dosimeter, which measures exposure to ionizing radiation. 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.

Applications

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 this, and in some cases give an alarm when a preset level is exceeded. Ionising radiation damage to the 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.

Types

Common types of wearable dosimeters for ionizing radiation include:

• Quartz fiber dosimeter
• Film badge dosimeter
• Thermoluminescent dosimeter
• Solid state (MOSFET or silicon diode) dosimeter

The quartz fiber dosimeters have to be prepared, usually daily, with a positive charge from either a hand-wound or battery-powered charging unit. 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 Both the quartz and film badge type are being superseded by the TLD and electronic semiconductor type, which can have a number of sophisticated functions such as alarming at preset levels and live readout of dose accumulated.

Industrial process use

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). One can also carry out the dosimetry of neutron radiation with a few specialised devices such as superheated drop detectors.

Gallery

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  Russian dosimeter

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  View through the above fiber dosimeter showing a reading

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  Russian Sosna radiometer-dosimeter (Front view)

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  Russian Sosna radiometer-dosimeter (Rear view)

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  Russian Radex RD1503

See also

• Comparison of dosimeters
• Geiger counter
• Scintillation counter
• Richard R. Rosenthal
• Royal Observer Corps
• Operational instruments of the Royal Observer Corps

External links

• A photographic list of radiation dosimeters
• Space Radiation Dosimetry: Lessons Learned and Recommendations