A radiation dosimeter is a device that measures the dose uptake of external

ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...

. It is worn by the person being monitored when used as a personal dosimeter, and is a record of the radiation dose received. Modern

electronic personal dosimeter The electronic personal dosimeter (EPD) is a modern electronic dosimeter for estimating uptake of ionising radiation equivalent dose, dose of the individual wearing it for radiation protection purposes. The electronic personal dosimeter has the a ...

s can give a continuous readout of cumulative dose and current dose rate, and can warn the wearer with an audible alarm when a specified dose rate or a cumulative dose is exceeded. Other dosimeters, such as thermoluminescent or film types, require processing after use to reveal the cumulative dose received, and cannot give a current indication of dose while being worn.

Personal dosimeters

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 related to the total dose received, for which the SI unit is the sievert.

Radiographer Radiographers, also known as radiology technologists, radiologic technologists, diagnostic radiographers and medical radiation technologists, are healthcare professionals who specialise in the imaging of human anatomy for the diagnosis and tr ...

nuclear power plant A nuclear power plant (NPP), also known as a nuclear power station (NPS), nuclear generating station (NGS) or atomic power station (APS) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power st ...

workers, doctors using

radiotherapy Radiation therapy or radiotherapy (RT, RTx, or XRT) is a treatment using ionizing radiation, generally provided as part of cancer therapy to either kill or control the growth of malignant cells. It is normally delivered by a linear particle ...

, HAZMAT workers, and other people in situations that involve handling radionuclides are often 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 doses for regulatory purposes. Dosimeters are typically worn on the outside of clothing, a "whole body" dosimeter is worn on the chest or torso to represent dose to the whole body. This location monitors exposure of most vital organs and represents the bulk of body mass. Additional dosimeters can be worn to assess dose to extremities or in radiation fields that vary considerably depending on orientation of the body to the source.

Electronic personal dosimeters

The electronic personal dosimeter, the most commonly used type, 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

Metal–oxide–semiconductor field-effect transistor dosimeters 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 2μm ). 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

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which is conventionally

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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 and aluminum oxides are also proposed as a radiation dosimeters.

PIN dosimeters

PIN diodes are often used by military personnel for measuring radiation dosage.

Scintillation counter

A scintillation counter detects ionizing radiation by measuring the light emitted from a scintillator, giving a measurement of radiation levels almost instantly. Like thermoluminescent crystals, scintillation materials begin to glow when exposed to radiation. Unlike thermoluminescent crystals, which store absorbed radiation to measure accumulated doses over a period of time, scintillation materials release light immediately, and do not need to be heated.

Thermoluminescent dosimeter

A thermoluminescent dosimeter measures ionizing radiation exposure by measuring the intensity of light emitted from a Dy or B doped crystal in the detector when heated. The intensity of light emitted is dependent upon the radiation exposure. These were once sold surplus and one format once used by submariners and nuclear workers resembled a dark green wristwatch containing the active components and a highly sensitive IR wire ended diode mounted to the doped LiF2 glass chip that when the assembly is precisely heated (hence thermoluminescent) emits the stored radiation as narrow band infrared light until it is depleted The main advantage is that the chip records dosage passively until exposed to light or heat so even a used sample kept in darkness can provide valuable scientific data.

Legacy types of dosimeters

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. They are now mostly superseded by electronic personal dosimeters and thermoluminescent dosimeters.

Quartz fiber dosimeter

These use the property of a quartz fiber to measure the static electricity held on the fiber. Before use by the wearer a dosimeter is charged to a high voltage, causing the fiber to deflect due to electrostatic repulsion. As the gas in the dosimeter chamber becomes ionized by radiation the charge leaks away, causing the fiber to straighten and thereby indicate the amount of dose received against a graduated scale, which is viewed by a small in-built microscope. They are only used for short durations, such as a day or a shift, as they can suffer from charge leakage, which gives a false high reading. However they are immune to EMP so were used during the Cold War as a failsafe method of determining radiation exposure. They are now largely superseded by electronic personal dosimeters for short term monitoring.

Geiger tube dosimeter

These use a conventional Geiger–Müller tube, typically a ZP1301 or similar energy-compensated tube, requiring between 600 and 700V and pulse detection components. The display on most is a bubble or miniature LCD type with 4 digits and a discrete counter integrated chip such as 74C925/6. LED units usually have a button to turn the display on and off for longer battery life, and an infrared emitter for count verification and calibration. The voltage is derived from a separate pinned or wire-ended module that often uses a unijunction transistor driving a small step-up coil and multiplier stage. While expensive, it is reliable over time and especially in high-radiation environments, sharing this trait with tunnel diodes, though the encapsulants, inductors and capacitors have been known to break down internally over time. These have the disadvantage that the stored dose in becquerels or microsieverts is volatile and vanishes if the power supply is disconnected, though there can be a low-leakage capacitor to preserve the memory for short periods without a battery. Because of this, most units use long-life batteries and high-quality contacts. Recently-designed units log dose over time to non-volatile memory, such as a 24C256 chip so it may be read out via a serial port.

Dosimetry dose quantities

The operational quantity for personal dosimetry is the personal dose equivalent, which is defined by the International Commission on Radiological Protection as the dose equivalent in soft tissue at an appropriate depth, below a specified point on the human body. The specified point is usually given by the position where the individual’s dosimeter is worn.

Instrument and dosimeter response

This is an actual reading obtained from such as an ambient dose

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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. The dosimeter plays an important role within the international

radiation protection Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposu ...

system developed by the International Commission on Radiological Protection and the International Commission on Radiation Units and Measurements. This is shown in the accompanying diagram.

Dosimeter calibration

The "slab" phantom is used to represent the human torso for calibration of whole body dosimeters. This replicates the radiation scattering and absorption effects of the human torso. The

International Atomic Energy Agency The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear technology, nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was ...

states "The slab phantom is 300 mm × 300 mm × 150 mm depth to represent the human torso".International Atomic Energy Agency safety report 16

Radiation related measurement quantities

Process irradiation verification

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.

Dosimeters as a tracking device

A Soviet KGB spy "Raduga" (Rainbow) dosimeter, radiation tracking device was used by deliberately contaminating items such as money, artworks, documents, propaganda literature etc. with a nuclear radiation signature which can then be tracked using this device which would vibrate when in proximity to the radiation. The process was utilized as a way of catching thieves and corrupt officials and locating hidden stashes.

Gallery

File:Direct-reading dosimeter.jpg, Quartz-fiber dosimeter – now largely superseded File:Dosimeter ablesung.jpg, View of quartz fiber dosimeter reading File:Chromoradiometer science museum.jpg, ''Chromoradiometer'' or colour dosimeter by Guido Holzknecht (1902) File:dosimeter sosna front.jpg, Russian Sosna radiometer-dosimeter (Front view), File:dosimeter sosna back.jpg, Russian Sosna radiometer-dosimeter (Rear view) File:Chernobyl and Pripyat (4854347168).jpg, Ukrainian Terra-P dosimeter File:rd1503.jpg, Russian Radex RD1503 File:Soeks.jpg, Soeks 01M File:Geiger Counter Survey Meter "White Cat" Edition SA-05A.jpg, Swiss dosimeter SA-05A File:POLIMASTER-PM1603B.jpg, Polimaster PM1603B

References

External links

A photographic list of radiation dosimeters

Space Radiation Dosimetry: Lessons Learned and Recommendations

Polimaster PM1603B

Gamma Watch PM1208M - Geigerzähler Uhr von Polimaster

So Rad! Virtual Training Facilitates Faster Fielding of Personal Radiation Detection Tool to the Joint Force
{{Authority control Dosimeters Ionising radiation detectors Radiation protection