A radiation dosimeter is a device that measures dose uptake of external ionizing radiation. 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 dosimeters 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 Health physics, also referred to as the science of radiation protection, is the profession devoted to protecting people and their environment from potential radiation hazards, while making it possible to enjoy the beneficial uses of radiation. H ...

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 The sievert (symbol: SvNot be confused with the sverdrup or the svedberg, two non-SI units that sometimes use the same symbol.) is a unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizing rad ...

Radiographer Radiographers, also known as radiologic technologists, diagnostic radiographers and medical radiation technologists are healthcare professionals who specialize in the imaging of human anatomy for the diagnosis and treatment of pathology. Radi ...

s, nuclear power plant workers, doctors using radiotherapy,

HAZMAT Dangerous goods, abbreviated DG, are substances that when transported are a risk to health, safety, property or the environment. Certain dangerous goods that pose risks even when not being transported are known as hazardous materials ( syllabi ...

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 dose 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 organ In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...

s 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.

Modern types

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 The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...

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 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 The gate oxide is the dielectric layer that separates the gate terminal of a MOSFET (metal-oxide-semiconductor field-effect transistor) from the underlying source and drain terminals as well as the conductive channel that connects source and drain ...

of MOSFET which is conventionally

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

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 The threshold voltage, commonly abbreviated as Vth or VGS(th), of a field-effect transistor (FET) is the minimum gate-to-source voltage (VGS) that is needed to create a conducting path between the source and drain terminals. It is an important s ...

of the MOSFET. This change in

is proportional to radiation dose. Alternate high-k gate dielectrics like hafnium dioxide and aluminum oxides are also proposed as a radiation dosimeters.

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 type

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 Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...

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-Muller tube typically a ZP1301 or similar energy compensated tube requiring between 600 and 700V and pulse detection components. The display on most was a bubble or miniature LCD type with 4 digits and a discrete counter IC such as 74C925/6, LED units usually have a button to enable the display for long 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 which though expensive 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

becquerel The becquerel (; symbol: Bq) is the unit of radioactivity in the International System of Units (SI). One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. For applications relatin ...

or microsievert count is volatile and vanishes if the power supply gets disconnected though there can be a low leakage capacitor to prevent short term battery disconnection from impact disrupting the memory. The fix is to use a long life battery, knurled high quality contacts and security screws to hold the typically glass front panel in place, though more recent units log counts versus time to a high capacity non-volatile memory such as 24C256 so it can 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 The International Commission on Radiological Protection (ICRP) is an independent, international, non-governmental organization, with the mission to protect people, animals, and the environment from the harmful effects of ionising radiation. Its r ...

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 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. The dosimeter plays an important role within the international radiation protection system developed by the International Commission on Radiological Protection and the

International Commission on Radiation Units and Measurements The International Commission on Radiation Units and Measurements (ICRU) is a standardization body set up in 1925 by the International Congress of Radiology, originally as the X-Ray Unit Committee until 1950. Its objective "is to develop concepts, de ...

. 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 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 Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed o ...

(Gy). The dosimeter is located on or adjacent to the items being irradiated during the process as a validation of dose levels received.

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

References

External links

A photographic list of radiation dosimeters

Space Radiation Dosimetry: Lessons Learned and Recommendations
{{Authority control Dosimeters Ionising radiation detectors Radiation protection