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A radiation dosimeter is a device that measures exposure to ionizing radiation. It has two main uses: for human radiation protection and for measurement of dose in both medical and industrial processes.[1][2][3]

Personal dosimeters[4][edit]

The personal ionising radiation dosimeter is of fundamental importance in the disciplines of radiation dosimetry and radiation health physics and is primarily used to estimate the radiation dose deposited in an individual wearing the device.

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. Workers exposed to radiation, such as radiographers, nuclear power plant workers, doctors using radiotherapy, those in laboratories using radionuclides, and HAZMAT teams are required to wear dosimeters so a record of occupational exposure can be made. Such devices are known as "legal dosimeters" if they have been approved for use in recording personnel dose for regulatory purposes.

Dosimeters can be worn to obtain a whole body dose and there are also specialist types that can be worn on the fingers or clipped to headgear, to measure the localised body irradiation for specific activities.

Types[edit]

Common types of personal dosimeters for ionizing radiation include:

Electronic personal dosimeter (EPD)[edit]

The electronic personal dosimeter (EPD) is an electronic device that has a number of sophisticated functions, such as continual monitoring which allows alarm warnings at preset levels and live readout of dose accumulated. These are especially useful in high dose areas where residence time of the wearer is limited due to dose constraints. The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times.

MOSFET dosimeter[edit]

MOSFET dosimeters [5] are now used as clinical dosimeters for radiotherapy radiation beams. The main advantages of MOSFET devices are:

1. The MOSFET dosimeter is direct reading with a very thin active area (less than 2 μm).

2. The physical size of the MOSFET when packaged is less than 4 mm.

3. The post radiation signal is permanently stored and is dose rate independent.

Gate oxide of MOSFET which is conventionally silicon dioxide is an active sensing material in MOSFET dosimeters. Radiation creates defects (acts like electron-hole pairs) in oxide, which in turn affects the threshold voltage of the MOSFET. This change in threshold voltage is proportional to radiation dose. Alternate high-k gate dielectrics like Hafnium dioxide[6] and Aluminum oxides are also proposed as a radiation dosimeters.

Film badge dosimeter[edit]

Main article: Film badge dosimeter

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.

Quartz fiber dosimeter[edit]

Quartz fiber dosimeters are charged to a high voltage. As the gas in the dosimeter chamber becomes ionized by radiation the charge leaks away, causing the fiber indicator to change against a graduated scale.[7]

Thermoluminescent dosimeter (TLD)[edit]

A thermoluminescent dosimeter measures ionizing radiation exposure by measuring the intensity of visible light emitted from a crystal in the detector when heated. The intensity of light emitted is dependent upon the radiation exposure.

Both the quartz fiber and film badge types are being superseded by the TLD and the EPD.


Radiation protection dose quantities[edit]

Main article: sievert
External radiation dose quantities used in radiological protection - based on ICRU report 57

The dosimeter plays an important role within the international radiation protection system developed by the International Commission on Radiological Protection (ICRP) and the International Commission on Radiation Units and Measurements (ICRU). This is shown in the accompanying diagram.

Protection quantities[edit]

The protection quantities are used as "limiting quantities" to specify exposure limits to ensure that the occurrence of stochastic health effects is kept below unacceptable levels and that tissue reactions are avoided.[8][9][10] These quantities cannot be practically measured and are a calculated value of irradiation of organs of the human body, which is arrived at by using an anthropomorphic phantom. This is a 3D computational model of the human body which attempts to take into account a number of complex effects such as body self-shielding and internal scattering of radiation.[11]

As protection quantities cannot practically be measured, operational quantities are used to relate them to practical radiation instrument and dosimeter responses.[12]

Operational quantities[edit]

Operational quantities are aimed at providing an estimate or upper limit for the value of the protection quantities related to an exposure. They are used in practical regulations or guidance. These relate real-life operational instrument measurements and responses to the calculated protection quantities.[13]

Personal dose equivalent, Hp(d), is defined by the ICRP as the dose equivalent in soft tissue at an appropriate depth, d, below a specified point on the human body. The specified point is usually given by the position where the individual’s dosimeter is worn.[14]

Instrument and dosimeter response[edit]

This is an actual reading obtained from such as an ambient dose gamma monitor, or a personal dosimeter. The dosimeter is calibrated in a known radiation field to ensure display of accurate operational quantities and allow a relationship to known health effect. The personal dose equivalent is used to assess dose uptake, and allow regulatory limits to be met. It is the figure usually entered into the records of external dose for occupational radiation workers.

Dosimeter calibration[edit]

The "slab" phantom is used to represent the human torso for calibration of whole body dosimeters. The IAEA states "The slab phantom is 300 mm × 300 mm × 150 mm depth to represent the human torso".[15]

Process irradiation verification[edit]

Manufacturing processes that treat products with ionizing radiation, such as food irradiation, use dosimeters to calibrate doses deposited in the matter being irradiated. These usually must have a greater dose range than personal dosimeters, and doses are normally measured in the unit of absorbed dose: the gray (Gy). The dosimeter is located on or adjacent to the items being irradiated during the process as a validation of dose levels received.


Gallery[edit]

See also[edit]

References[edit]

  1. ^ http://iopscience.iop.org/0031-9155/59/20/R303/article
  2. ^ Advances in kilovoltage x-ray beam dosimetry in http://dx.doi.org/10.1088/0031-9155/59/6/R183
  3. ^ Polymer gel dosimetry review in http://dx.doi.org/10.1088/0031-9155/55/5/R01
  4. ^ phd1
  5. ^ http://www.mosfet.ca/global/pdf/technotes/te_4.pdf
  6. ^ V. S. Senthil Srinivasan and Arun Pandya, ″Dosimetry aspects of hafnium oxide metal-oxide-semiconductor (MOS) capacitor″, [1] Thin Solid Films Volume 520, Issue 1, 31 October 2011, Pages 574–577
  7. ^ Frame, Paul (2007-07-25). "Pocket Chambers and Pocket Dosimeters". Health physics historical instrument museum collection. Oak Ridge Associated Universities. Retrieved 2008-11-08. 
  8. ^ ICRP publication 103, paragraph 112
  9. ^ ICRP publication 103, paragraph B50
  10. ^ "In 1991, the International Commission on Radiological Protection (ICRP) [7] recommended a revised system of dose limitation, including specification of primary limiting quantities for radiation protection purposes. These protection quantities are essentially unmeasurable" - IAEA Safety report 16
  11. ^ ICRP publication 103, paragraph B64
  12. ^ ICRP publication 103, paragraph B146
  13. ^ ICRP publication 103, paragraph B147
  14. ^ ICRP pub 103 glossary
  15. ^ IAEA safety report 16

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Dosimeter — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.

3838 news items

Medgadget.com (blog)

Medgadget.com (blog)
Tue, 26 Apr 2016 09:30:00 -0700

Global Personal Dosimeter Industry 2016 and analysis by 2020 analyzed the world's main region market size, share, trends, conditions, including the product price, profit, capacity, production, capacity utilization, supply, demand and industry growth ...

Safety+Health magazine

Safety+Health magazine
Sat, 23 Apr 2016 21:20:33 -0700

The Casella dBadge2, designed for use in explosive environments, is certified intrinsically safe – it will not ignite an explosion even under fault conditions. Equipped with Bluetooth 4.0 connectivity, the dBadge2 allows users to wirelessly control ...

Albuquerque Business First

Albuquerque Business First
Mon, 02 May 2016 13:37:30 -0700

The technology is expected to be a significant advancement over the current stock of dosimeter and radiation reader technology that was developed in the 1960s, which is considered outdated. Aquila Group president Judy Beckes Talcott said that the ...

Kölnische Rundschau

Kölnische Rundschau
Mon, 25 Apr 2016 01:48:45 -0700

„Es bleibt ein beklemmendes Gefühl zurück“, stellte eine Zuschauerin fest und wollte von den Machern des gerade gesehenen Films wissen, ob sie mit Idealismus darauf hoffen, mit ihrem Werk etwas zu bewegen. Ein Mann zog den Schluss, dass man jungen ...
 
Santa Fe New Mexican
Sat, 30 Apr 2016 22:21:08 -0700

Your Waste Isolation Pilot Plant site photos from Carlsbad (“Journey to the center of WIPP,” April 17) made my hair stand on end. Just because radiation is invisible, silent and hidden from view (without the help of a dosimeter), it doesn't mean it ...

Washington Post

Washington Post
Tue, 26 Apr 2016 04:05:49 -0700

Working in the highly restricted zone, which involves using a dosimeter and suiting up in masks and respirators, is an “emotionally polarizing experience,” Beasley said. Wildlife or evidence of it is “everywhere,” he said, making it feel like a ...

The Columbian

The Columbian
Thu, 28 Apr 2016 05:56:15 -0700

Working in the highly restricted zone, which involves using a dosimeter and suiting up in masks and respirators, is an “emotionally polarizing experience,” Beasley said. Wildlife or evidence of it is “everywhere,” he said, making it feel like a ...

Fox News

Fox News
Tue, 26 Apr 2016 12:34:36 -0700

At one point we ventured within four miles of the mangled energy plant and our cell phone-sized dosimeter soared to indicate dangerous radiation levels—10 times higher than what is considered safe. I can still hear the haunting creak of dilapidated ...
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