Radiation Dosimetry

An electronic personal dosimeter is modern dosimeter, which can give a continuous readout of cumulative dose and current dose rate, and can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded. EPDs are especially useful in high dose areas where residence time of the wearer is limited due to dose constraints.

Advantages and Disadvantages of Electronic Personal Dosimeters

Advantages of Electronic Personal Dosimeters

• EPDs are able to display a direct reading of the detected dose and dose rate in real time.
• EPDs have a dose rate alarm, and a dose alarm, which can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded.
• The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times.
• EPDs are capable of measuring a wide radiation dose range from routine (μSv) levels to emergency levels (hundreds mSv or units of Sieverts) with high precision

Disadvantages of Electronic Personal Dosimeters

• EPDs are generally the most expensive dosimeters.
• EPDs are generally large in size.
• EPDs are used to measure and record radiation exposure due to gamma rays, X-rays, sometimes beta particles. For neutrons, TLDs are more capable.

See also:

EPD

An electronic personal dosimeter is modern dosimeter, which can give a continuous readout of cumulative dose and current dose rate, and can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded. EPDs are especially useful in high dose areas where residence time of the wearer is limited due to dose constraints.

MOSFET Dosimeter

MOSFET dosimeter is a small portable device for monitoring and direct reading of radiation dose rate. Since it is based on the MOSFET transistor, the metal-oxide-semiconductor field-effect transistor (MOSFET), the principle of operation is similar as for semiconductor detectors.  MOSFET dosimeters are now used as clinical dosimeters for radiotherapy radiation beams. Their main advantage is their physical size, which is less than 4 mm². In radiation therapy dosimetry, MOSFET dosimeters often replace TLD dosimeters, since they offer immediate read out.

Principle of Operation of MOSFET Detectors  

The operation of MOSFET detectors is summarized in the following points:

• Ionizing radiation enters the sensitive volume of the detector and interacts with the semiconductor material.
• Particle passing through the detector ionizes the atoms of semiconductor, producing the electron-hole pairs. Electron-hole pairs are generated within the silicon dioxide by the incident radiation. Electrons, whose mobility in SiO₂ at room temperature is about 4 orders of magnitude greater than holes, quickly move out of the gate electrode while holes move in a stochastic fashion towards the Si/SiO₂ interface where they become trapped in long term sites, causing a negative threshold voltage shift (∆V_TH), which can persist for years.
• The difference in voltage shift before and after exposure can be measured, and is proportional to dose.

Advantages and Disadvantages of Electronic Personal Dosimeters

Advantages

• EPDs are able to display a direct reading of the detected dose and dose rate in real time.
• EPDs have a dose rate alarm, and a dose alarm, which can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded.
• The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times.
• EPDs are capable of measuring a wide radiation dose range from routine (μSv) levels to emergency levels (hundreds mSv or units of Sieverts) with high precision

Disadvantages

• EPDs are generally the most expensive dosimeters.
• EPDs are generally large in size.
• EPDs are used to measure and record radiation exposure due to gamma rays, X-rays, sometimes beta particles. For neutrons, TLDs are more capable.

See also:

Radiation Dosimeter

MOSFET dosimeter is a small portable device for monitoring and direct reading of radiation dose rate. Since it is based on the MOSFET transistor, the metal-oxide-semiconductor field-effect transistor (MOSFET), the principle of operation is similar as for semiconductor detectors.  MOSFET dosimeters are now used as clinical dosimeters for radiotherapy radiation beams. Their main advantage is their physical size, which is less than 4 mm². In radiation therapy dosimetry, MOSFET dosimeters often replace TLD dosimeters, since they offer immediate read out.

Principle of Operation of MOSFET Detectors  

The operation of MOSFET detectors is summarized in the following points:

• Ionizing radiation enters the sensitive volume of the detector and interacts with the semiconductor material.
• Particle passing through the detector ionizes the atoms of semiconductor, producing the electron-hole pairs. Electron-hole pairs are generated within the silicon dioxide by the incident radiation. Electrons, whose mobility in SiO₂ at room temperature is about 4 orders of magnitude greater than holes, quickly move out of the gate electrode while holes move in a stochastic fashion towards the Si/SiO₂ interface where they become trapped in long term sites, causing a negative threshold voltage shift (∆V_TH), which can persist for years.
• The difference in voltage shift before and after exposure can be measured, and is proportional to dose.

See also:

MOSFET

Self-reading dosimeters are field-readable devices worn on the body to measure accumulated dose. These are unpowered devices that do not contain a battery. Devices in this group include:

• Quartz fiber dosimeter. A quartz fiber dosimeter, sometimes called a self indicating pocket dosimeter (SIPD), is a pen-like device that measures the cumulative dose of ionizing radiation received by the device, usually over one work period.
• Self-developing photochemical cards. Self-developing photochemical card is a credit card sized, instant color developing emergency dosimeter. It is designed for monitoring exposure in a radiological incident for medical treatment triage and to minimize worry and panic.

They display the dose to the wearer using an analog scale or color indicator; they do not have alarm capabilities. Self-reading dosimeters are less precise devices applicable to situations where real-time information may be needed to make tactical decisions but where electronic dosimeters are not practical.

Quartz Fiber Dosimeter – Self Indicating Pocket Dosimeters

A quartz fiber dosimeter, sometimes called a self indicating pocket dosimeter (SIPD), is a pen-like device that measures the cumulative dose of ionizing radiation received by the device, usually over one work period. As the name implies, they are commonly worn in the pocket. The self indicating pocket dosimeter consists of an ionization chamber, with a volume of approximately two milliliters, which is sensitive to a desired radiation, a quartz fiber electrometer to measure the charge, and a microscope to read the fiber image off a scale. Inside the ionization chamber is a central wire anode, and attached to this wire anode is a metal coated quartz fiber.

Quartz fiber dosimeters are charged to a high voltage, and are usually used for one work period only. Electrostatic repulsion deflects the quartz fiber, and the greater the charge, the greater the deflection of the quartz fiber. As the dosimeter is exposed to radiation, ionization occurs in the surrounding chamber decreasing the charge on the electrode in proportion to the exposure. The deflection of the moveable quartz fiber electrode is projected by a light source through an objective lens to a calibrated scale and read through a microscope eyepiece. Self indicating pocket dosimeters are now being superseded by more modern types, such as electronic personal dosimeters.

See also:

Radiation Dosimeter

A quartz fiber dosimeter, sometimes called a self indicating pocket dosimeter (SIPD), is a pen-like device that measures the cumulative dose of ionizing radiation received by the device, usually over one work period. As the name implies, they are commonly worn in the pocket. The self indicating pocket dosimeter consists of an ionization chamber, with a volume of approximately two milliliters, which is sensitive to a desired radiation, a quartz fiber electrometer to measure the charge, and a microscope to read the fiber image off a scale. Inside the ionization chamber is a central wire anode, and attached to this wire anode is a metal coated quartz fiber.

Quartz fiber dosimeters are charged to a high voltage, and are usually used for one work period only. Electrostatic repulsion deflects the quartz fiber, and the greater the charge, the greater the deflection of the quartz fiber. As the dosimeter is exposed to radiation, ionization occurs in the surrounding chamber decreasing the charge on the electrode in proportion to the exposure. The deflection of the moveable quartz fiber electrode is projected by a light source through an objective lens to a calibrated scale and read through a microscope eyepiece. Self indicating pocket dosimeters are now being superseded by more modern types, such as electronic personal dosimeters.

See also:

Self-reading Dosimeters

Personal dosimetry is a key part of radiation dosimetry. Personal dosimetry is used primarily (but not exclusively) to determine doses to individuals who are exposed to radiation related to their work activities. These doses are usually measured by devices known as personal dosimeters. Dosimeters usually record a dose, which is the absorbed radiation energy measured in grays (Gy) or the equivalent dose measured in sieverts (Sv). A personal dosimeter is dosimeter, that is worn at the surface of the body by the person being monitored, and it  records of the radiation dose received. Personal dosimetry techniques vary and depend partly on whether the source of radiation is outside the body (external) or taken into the body (internal). Personal dosimeters are used to measure external radiation exposures. Internal exposures are typically monitored by measuring the presence of nuclear substances in the body, or by measuring nuclear substances excreted by the body.

Commercially available dosimeters range from low-cost, passive devices that store personnel dose information for later readout, to more expensive, battery operated devices that display immediate dose and dose rate information (typically an electronic personal dosimeter). Readout method, dose measurement range, size, weight, and price are important selection factors.

There are two kinds of dosimeters:

• Passive Dosimeters. Commonly used passive dosimeters are the Thermo Luminescent Dosimeter (TLD) and the film badge. A passive dosimeter produces a radiation-induced signal, which is stored in the device. The dosimeter is then processed and the output is analyzed.
• Active Dosimeters. To get a real time value of your exposure you can instead use an active dosimeter, typically an electronic personal dosimeter (EPD). An active dosimeter produces a radiation-induced signal and displays a direct reading of the detected dose or dose rate in real time.

The passive and the active dosimeters are often used together to complement each other. To estimate effective doses, dosimeters must be worn on a position of the body representative of its exposure, typically between the waist and the neck, on the front of the torso, facing the radioactive source. Dosimeters are usually worn on the outside of clothing, around the chest or torso to represent dose to the “whole body”. Dosimeters may also be worn on the extremities or near the eye to measure equivalent dose to these tissues.

The personal dosimeters in use today are not absolute instruments, but reference instruments. That means , they must be periodically calibrated. When a reference dosimeter is calibrated, a calibration factor can be determined. This calibration factor relates the exposure quantity to the reported dose. Validity of the calibration is demonstrated by maintaining traceability of the source used to calibrate the dosimeter. The traceability is achieved by comparison of the source with a “primary standard” at a reference calibration centre. In monitoring of individuals, the values of these operational quantities are taken as a sufficiently precise assessment of effective dose and skin dose, respectively, in particular, if their values are below the protection limits.

Example – Electronic Personal Dosimeter

An electronic personal dosimeter is modern dosimeter, which can give a continuous readout of cumulative dose and current dose rate, and can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded. EPDs are especially useful in high dose areas where residence time of the wearer is limited due to dose constraints.

Types of EPDs

EPDs are battery powered and most use either a small Geiger-Mueller (GM) tube or a semiconductor in which ionizing radiation releases charges resulting in measurable electric current.

• G-M counter. A Geiger counter consists of a Geiger-Müller tube (the sensing element which detects the radiation) and the processing electronics, which displays the result. G-M counters are mainly used for portable instrumentation due to its sensitivity, simple counting circuit, and ability to detect low-level radiation. Because of the large avalanche induced by any ionization, a Geiger counter takes a long time (about 1 ms) to recover between successive pulses. Therefore, Geiger counters are not able to measure high radiation rates due to the “dead time” of the tube.
• Semiconductor Detector. Semiconductor detectors are based on ionization in a solid (e.g. silicon) and include different types of solid-state devices with two terminals called diodes. For example a silicon diode, which has a p-i-n structure in which the intrinsic (i) region is sensitive to ionizing radiation, particularly X rays and gamma rays. Under reverse bias, an electric field extends across the intrinsic or depleted region. In this case, negative voltage is applied to the p-side and positive to the second one. Holes in the p-region are attracted from the junction towards the p contact and similarly for electrons and the n contact.
• Scintillation Detector. Some EPDs use a scintillating crystal such as sodium iodide (NaI) or cesium iodide (CsI) with a photodiode or photomultiplier tube to measure photons released by radiation.

Characteristics of EPDs

The electronic personal dosimeter, EPD, is able to display a direct reading of the detected dose or dose rate in real time. Electronic dosimeters may be used as a supplemental dosimeter as well a primary dosimeter. The passive dosimeters and the electronic personal dosimeters are often used together to complement each other. To estimate effective doses, dosimeters must be worn on a position of the body representative of its exposure, typically between the waist and the neck, on the front of the torso, facing the radioactive source. Dosimeters are usually worn on the outside of clothing, around the chest or torso to represent dose to the “whole body”. Dosimeters may also be worn on the extremities or near the eye to measure equivalent dose to these tissues.

The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times. The EPDs have a top mounted display to make them easy to read when they are clipped to your breast pocket. The digital display gives both dose and dose rate information usually in mSv and mSv/h. The EPD has a dose rate alarm, and a dose alarm. These alarms are programmable. Different alarms can be set for different activities.

For example:

• dose rate alarm at 100 μSv/h,
• dose alarm: 100 μSv.

If an alarm set point is reached, the relevant display flashes along with a red light, and quite a piercing noise is generated. You can clear the dose rate alarm by retreating to a lower radiation field, but you cannot clear the dose alarm until you get to a EPD reader. EPDs can also give a bleep for every 1 or 10 μSv they register. This gives you an audible indication of the radiation fields. Some EPDs have wireless communication capabilities. EPDs are capable of measuring a wide radiation dose range from routine (μSv) levels to emergency levels (hundreds mSv or units of Sieverts) with high precision, and may display the exposure rate as well as accumulated exposure values. Of the dosimeter technologies, electronic personal dosimeters are generally the most expensive, largest in size, and the most versatile.

DMC 3000 – Mirion Technologies Inc.

The DMC 3000 is an electronic radiation dosimeter, EPD, that provides dose and ambient dose rate readings for deep dose equivalent H_p(10). It is one of the most used EPDs on the market. It uses a Si chip detector with gamma sensitivity of 180 cps/R/h. This electronic personal dosimeter has the following characteristics:

• Energy response (X-ray and gamma) from 15 keV to 7 Mev.
• Dose measurement display range: between 1 μSv and 10 Sv.
• Rate measurement display range: between 10 μSv/hr and 10 Sv/h.

The device measures 3.3 x 1.9 x 0.7 inches and has options for being clipped to a pocket, belt, or lanyard. It is powered with rechargeable or AAA batteries with a battery life of up to 2,500 hours of continuous use. Audible and visual indicators signal a low battery condition. The device has a backlit, eight-digit LCD display; two-button navigation; and visual LED, audible, and vibrating alarm indicators. Calibration is expected to last 9 months under routine use and 2 years in storage. Data is stored in nonvolatile memory. The operating range for the dosimeter is from 14°F to 122°F and up to 90 percent relative humidity. It is drop tested to 1.5 meters. The DMC 3000 has optional external modules that expand the device’s detection and communication capabilities. These include a beta module that provides H_p(0,07) for beta radiation measurement; a neutron module that provides H_p(10) neutron radiation measurement; and a telemetry module that allows transmission of data to an external station.

See also: The Radiation Dosimeters for Response and Recovery Market Survey Report. National Urban Security Technology Laboratory. SAVER-T-MSR-4. <available from: https://www.dhs.gov/sites/default/files/publications/Radiation-Dosimeters-Response-Recovery-MSR_0616-508_0.pdf>.

Example – Neutron TLD

A thermoluminescent dosimeter, abbreviated as TLD,  is a passive radiation dosimeter, that measures ionizing radiation exposure by measuring the intensity of visible light emitted from a sensitive crystal in the detector when the crystal is heated. The intensity of light emitted is measure by TLD reader and it is dependent upon the radiation exposure. Thermoluminescent dosimeters was invented in 1954 by Professor Farrington Daniels of the University of Wisconsin-Madison. TLD dosimeters are applicable to situations where real-time information is not needed, but precise accumulated dose monitoring records are desired for comparison to field measurements or for assessing the potential for long term health effects. In dosimetry, both the quartz fiber and film badge types are being superseded by TLDs and EPDs (Electronic Personal Dosimeter).

Neutron Thermoluminescent Dosimeter – Neutron TLD

The personnel neutron dosimetry continues to be one of the problems in the field of radiation protection, as no single method provides the combination of energy response, sensitivity, orientation dependence characteristics and accuracy necessary to meet the needs of a personnel dosimeter.

The most commonly used personnel neutron dosimeters for radiation protection purposes are thermoluminescent dosimeters and albedo dosimeters. Both are based on this phenomenon – thermoluminescence. For this purpose, lithium fluoride (LiF) as sensitive material (chip) is widely used. Lithium fluoride TLD is used for gamma and neutron exposure (indirectly, using the Li-6 (n,alpha)) nuclear reaction. Small crystals of LiF (lithium fluoride) are the most common TLD dosimeters since they have the same absorption properties as soft tissue. Lithium has two stable isotopes, lithium-6 (7.4 %) and lithium-7 (92.6 %). Li-6 is the isotope sensitive to neutrons. In order to record neutrons, LiF crystal dosimeters may be enriched in lithium-6 to enhance the lithium-6 (n,alpha) nuclear reaction. The efficiency of the detector depends on the energy of the neutrons. Because the interaction of neutrons with any element is highly dependent on energy, making a dosimeter independent of the energy of neutrons is very difficult. In order to separate thermal neutrons and photons, LiF dosimeters are mostly utilized, containing different percentage of lithium-6. LiF chip enriched in lithium-6, which is very sensitive to thermal neutrons and LiF chip containing very little of lithium-6, which has a negligible neutron response.

The principle of neutron TLDs is then similar as for gamma radiation TLDs. In the LiF chip, there are impurities (e.g. manganese or magnesium), which produce trap states for energetic electrons. The impurity causes traps in the crystalline lattice where, following irradiation (to alpha radiation), electrons are held. When the crystal is warmed, the trapped electrons are released and light is emitted. The amount of light is related to the dose of radiation received by the crystal.

Thermoluminiscent Albedo Neutron Dosimeter

Albedo neutron dosimetry is based on the effect of moderation and backscattering of neutrons by the human body. Albedo, the latin word for “whiteness”, was defined by Lambert as the fraction of the incident light reflected diffusely by a surface. Moderation and backscattering of neutrons by the human body creates a neutron flux at the body surface in the thermal and intermediate energy range. These backscattered neutrons called albedo neutrons, can be detected by a dosimeter (usually a LiF TLD chip), placed on the body which is designed to detect thermal neutrons. Albedo dosimeters have been found to be the only dosimeters which can measure doses due to neutrons over the whole range of energies. Usually, two types of lithium fluoride are used to separate doses contributed by gamma-rays and neutrons. LiF chip enriched in lithium-6, which is very sensitive to thermal neutrons and LiF chip containing very little of lithium-6, which has a negligible neutron response.

Radiation Dose Measuring and Monitoring

In previous chapters, we described the equivalent dose and the effective dose. But these doses are not directly measurable. For this purpose, the ICRP  has introduced and defined a set of operational quantities, which can be measured and which are intended to provide a reasonable estimate for the protection quantities. These quantities aim to provide a conservative estimate for the value of the protection quantities related to an exposure avoiding both underestimation and too much overestimation.

Numerical links between these quantities is represented by conversion coefficients, which are defined for a reference person. It is very important that an internationally agreed set of conversion coefficients is available for general use in radiological protection practice for occupational exposures and exposures of the public. For the calculation of conversion coefficients for external exposure, computational phantoms are used for dose assessment in various radiation fields. For the calculation of dose coefficients from intakes of radionuclides, biokinetic models for radionuclides, reference physiological data, and computational phantoms are used.

A set of evaluated data of conversion coefficients for protection, and operational quantities for external exposure to mono-energetic photon, neutron, and electron radiation under specific irradiation conditions is published in reports  (ICRP, 1996b, ICRU, 1997).

In general, the ICRP defines operational quantities for area and individual monitoring of external exposures. The operational quantities for area monitoring are:

• Ambient dose equivalent, H*(10). The ambient dose equivalent is an operational quantity for area monitoring of strongly penetrating radiation.
• Directional dose equivalent, H’ (d,Ω). The directional dose equivalent is an operational quantity for area monitoring of weakly penetrating radiation.

The operational quantities for individual monitoring are:

• Personal dose equivalent, H_p(0.07). The H_p(0.07) dose equivalent is an operational quantity for individual monitoring for the assessment of the dose to the skin and to the hands and feet.
• Personal dose equivalent, H_p(10). The H_p(10) dose equivalent is an operational quantity for individual monitoring for the assessment of effective dose.

Special Reference: ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).

Dose Limits

See also: Dose Limits

Dose limits are split into two groups, the public, and occupationally exposed workers. According to ICRP, occupational exposure refers to all exposure incurred by workers in the course of their work, with the exception of

1. excluded exposures and exposures from exempt activities involving radiation or exempt sources
2. any medical exposure
3. the normal local natural background radiation.

The following table summarizes dose limits for occupationally exposed workers and for the public:

According to the recommendation of the ICRP in its statement on tissue reactions of 21. April 2011, the equivalent dose limit for the lens of the eye for occupational exposure in planned exposure situations was reduced from 150 mSv/year to 20 mSv/year, averaged over defined periods of 5 years, with no annual dose in a single year exceeding 50 mSv.

Limits on effective dose are for the sum of the relevant effective doses from external exposure in the specified time period and the committed effective dose from intakes of radionuclides in the same period. For adults, the committed effective dose is computed for a 50-year period after intake, whereas for children it is computed for the period up to age 70 years. The effective whole-body dose limit of 20 mSv is an average value over five years. The real limit is 100 mSv in 5 years, with not more than 50 mSv in any one year.

See also:

Radiation Dosimetry

EPD – Electronic Personal Dosimeter

An electronic personal dosimeter is modern dosimeter, which can give a continuous readout of cumulative dose and current dose rate, and can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded. EPDs are especially useful in high dose areas where residence time of the wearer is limited due to dose constraints.

Characteristics of EPDs

The electronic personal dosimeter, EPD, is able to display a direct reading of the detected dose or dose rate in real time. Electronic dosimeters may be used as a supplemental dosimeter as well a primary dosimeter. The passive dosimeters and the electronic personal dosimeters are often used together to complement each other. To estimate effective doses, dosimeters must be worn on a position of the body representative of its exposure, typically between the waist and the neck, on the front of the torso, facing the radioactive source. Dosimeters are usually worn on the outside of clothing, around the chest or torso to represent dose to the “whole body”. Dosimeters may also be worn on the extremities or near the eye to measure equivalent dose to these tissues.

The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times. The EPDs have a top mounted display to make them easy to read when they are clipped to your breast pocket. The digital display gives both dose and dose rate information usually in mSv and mSv/h. The EPD has a dose rate alarm, and a dose alarm. These alarms are programmable. Different alarms can be set for different activities.

For example:

• dose rate alarm at 100 μSv/h,
• dose alarm: 100 μSv.

Advantages and Disadvantages of Electronic Personal Dosimeters

Advantages of Electronic Personal Dosimeters

• EPDs are able to display a direct reading of the detected dose and dose rate in real time.
• EPDs have a dose rate alarm, and a dose alarm, which can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded.
• The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times.
• EPDs are capable of measuring a wide radiation dose range from routine (μSv) levels to emergency levels (hundreds mSv or units of Sieverts) with high precision

Disadvantages of Electronic Personal Dosimeters

• EPDs are generally the most expensive dosimeters.
• EPDs are generally large in size.
• EPDs are used to measure and record radiation exposure due to gamma rays, X-rays, sometimes beta particles. For neutrons, TLDs are more capable.

Film Badge Dosimeter

Film badges, film badge dosimeters, are small portable devices for monitoring cumulative radiation dose due to ionizing radiation. Principle of operation is similar as for X-ray pictures. The badge consists of two parts: photographic film, and a holder. The film is contained inside a badge. The piece of photographic film that is the sensitive material and it must be removed monthly and developed. The more radiation exposure, the more blackening of the film. The blackening of the film is linear to the dose, and doses up to about 10 Gy can be measured.

Film badge dosimeters are for one-time use only, they cannot be reused. A film badge dosimeter is dosimeter, that is worn at the surface of the body by the person being monitored, and it records of the radiation dose received. The film badge is used to measure and record radiation exposure due to gamma rays, X-rays and beta particles. The badge incorporates a series of filters (lead, tin, cadmium and plastic) to determine the quality of the radiation. To monitor beta particle emission, the filters use various densities of plastic or even label material. It is typical for a single badge to contain a series of filters of different thicknesses and of different materials; the precise choice may be determined by the environment to be monitored.

Examples of filters:

• There is an open window that makes it possible for weaker radiations to reach the film.
• A thin plastic filter which attenuates beta radiation but passes all other radiations
• A thick plastic filter which passes all but the lowest energy photon radiation and absorbs all but the highest beta radiation.
• A dural filter which progressively absorbs photon radiation at energies below 65 keV as well as beta radiation.
• A tin/lead filter of a thickness which allows an energy independent dose response of the film over the photon energy range 75 keV to 2 MeV.
• A cadmium lead filter can be used for thermal neutrons detection. The capture of neutrons ((n,gamma) reactions) by cadmium produces gamma rays which blacken the film thus enabling assessment of exposure to neutrons.

Advantages and Disadvantages of Film Dosimeters

Advantages of Film Dosimeters

• A film badge as a personnel monitoring device are very simple and therefore they are not expensive.
• A film badge provides a permanent record.
• Film badge dosimeters are very reliable.
• A film badge is used to measure and record radiation exposure due to gamma rays, X-rays and beta particles.

Disadvantages of Film Dosimeters

• Film dosimeters usually cannot be read on site instead of they have to be sent away for developing.
• Film dosimeters are for one-time use only, they cannot be reused.
• Exposures of less than 0.2 mSv (20 millirem) of gamma radiation cannot be accurately measured.

See also:

EPD

EPD – Electronic Personal Dosimeter

An electronic personal dosimeter is modern dosimeter, which can give a continuous readout of cumulative dose and current dose rate, and can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded. EPDs are especially useful in high dose areas where residence time of the wearer is limited due to dose constraints.

Characteristics of EPDs

The electronic personal dosimeter, EPD, is able to display a direct reading of the detected dose or dose rate in real time. Electronic dosimeters may be used as a supplemental dosimeter as well a primary dosimeter. The passive dosimeters and the electronic personal dosimeters are often used together to complement each other. To estimate effective doses, dosimeters must be worn on a position of the body representative of its exposure, typically between the waist and the neck, on the front of the torso, facing the radioactive source. Dosimeters are usually worn on the outside of clothing, around the chest or torso to represent dose to the “whole body”. Dosimeters may also be worn on the extremities or near the eye to measure equivalent dose to these tissues.

The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times. The EPDs have a top mounted display to make them easy to read when they are clipped to your breast pocket. The digital display gives both dose and dose rate information usually in mSv and mSv/h. The EPD has a dose rate alarm, and a dose alarm. These alarms are programmable. Different alarms can be set for different activities.

For example:

• dose rate alarm at 100 μSv/h,
• dose alarm: 100 μSv.

Advantages and Disadvantages of Electronic Personal Dosimeters

Advantages of Electronic Personal Dosimeters

• EPDs are able to display a direct reading of the detected dose and dose rate in real time.
• EPDs have a dose rate alarm, and a dose alarm, which can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded.
• The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times.
• EPDs are capable of measuring a wide radiation dose range from routine (μSv) levels to emergency levels (hundreds mSv or units of Sieverts) with high precision

Disadvantages of Electronic Personal Dosimeters

• EPDs are generally the most expensive dosimeters.
• EPDs are generally large in size.
• EPDs are used to measure and record radiation exposure due to gamma rays, X-rays, sometimes beta particles. For neutrons, TLDs are more capable.

TLD – Thermoluminescent Dosimeter

A thermoluminescent dosimeter, abbreviated as TLD,  is a passive radiation dosimeter, that measures ionizing radiation exposure by measuring the intensity of visible light emitted from a sensitive crystal in the detector when the crystal is heated. The intensity of light emitted is measure by TLD reader and it is dependent upon the radiation exposure. Thermoluminescent dosimeters was invented in 1954 by Professor Farrington Daniels of the University of Wisconsin-Madison. TLD dosimeters are applicable to situations where real-time information is not needed, but precise accumulated dose monitoring records are desired for comparison to field measurements or for assessing the potential for long term health effects. In dosimetry, both the quartz fiber and film badge types are being superseded by TLDs and EPDs (Electronic Personal Dosimeter).

Advantages and Disadvantages of TLDs

Advantages of TLDs

• TLDs are able to measure a greater range of doses in comparison with film badges.
• Doses from TLDs may be easily obtained.
• TLDs can be read on site instead of being sent away for developing.
• TLDs are easily reusable.

Disadvantages of TLDs

• Each dose cannot be read out more than once.
• The readout process effectively “zeroes” the TLD.

See also:

EPD

TLD – Thermoluminescent Dosimeter

A thermoluminescent dosimeter, abbreviated as TLD,  is a passive radiation dosimeter, that measures ionizing radiation exposure by measuring the intensity of visible light emitted from a sensitive crystal in the detector when the crystal is heated. The intensity of light emitted is measure by TLD reader and it is dependent upon the radiation exposure. Thermoluminescent dosimeters was invented in 1954 by Professor Farrington Daniels of the University of Wisconsin-Madison. TLD dosimeters are applicable to situations where real-time information is not needed, but precise accumulated dose monitoring records are desired for comparison to field measurements or for assessing the potential for long term health effects. In dosimetry, both the quartz fiber and film badge types are being superseded by TLDs and EPDs (Electronic Personal Dosimeter).

Advantages and Disadvantages of TLDs

Advantages of TLDs

• TLDs are able to measure a greater range of doses in comparison with film badges.
• Doses from TLDs may be easily obtained.
• TLDs can be read on site instead of being sent away for developing.
• TLDs are easily reusable.

Disadvantages of TLDs

• Each dose cannot be read out more than once.
• The readout process effectively “zeroes” the TLD.

OSL Dosimeter

The OSL dosimetry (Optically Stimulated Luminescence) is a method that has established itself in the whole-body dosimetry. As can be deduced, this method is based on optically stimulated luminescence. The OSL dosimeter provides a very high degree of sensitivity by giving an accurate reading as low as 1 mrem for x-ray and gamma ray photons with energies ranging from 5 keV to greater than 40 MeV. OSL dosimeters are designed to provide X, gamma, beta and neutron radiation monitoring using OSL technology. OSL dosimeters are applicable to situations where real-time information is not needed, but precise accumulated dose monitoring records are desired for comparison to field measurements or for assessing the potential for long term health effects. In diagnostic imaging the increased sensitivity of the OSL dosimeter makes it ideal for monitoring employees working in low-radiation environments and for pregnant workers. OSL dosimeters offer advantages that include the ability to be re-read and a high sensitivity (low minimum measurable dose), and they have become popular because of these favourable properties.

OSL materials (e.g. beryllium oxide ceramic) contain defects in their crystal structure that trap electrons released by exposure to radiation. In TLDs, the trapped electrons are subsequently freed by stimulation with heat, while OSL uses stimulation with light. After stimulation by light, the detector releases the stored energy in the form of light, i.e., it is stimulated to emit light. The light output measured with photomultipliers is a measure unit for the dose. In comparison with TLDs, their major difference is that luminescence is produced by a light beam, rather than by heat.

See also:

TLD

EPD – Electronic Personal Dosimeter

An electronic personal dosimeter is modern dosimeter, which can give a continuous readout of cumulative dose and current dose rate, and can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded. EPDs are especially useful in high dose areas where residence time of the wearer is limited due to dose constraints.

Characteristics of EPDs

The electronic personal dosimeter, EPD, is able to display a direct reading of the detected dose or dose rate in real time. Electronic dosimeters may be used as a supplemental dosimeter as well a primary dosimeter. The passive dosimeters and the electronic personal dosimeters are often used together to complement each other. To estimate effective doses, dosimeters must be worn on a position of the body representative of its exposure, typically between the waist and the neck, on the front of the torso, facing the radioactive source. Dosimeters are usually worn on the outside of clothing, around the chest or torso to represent dose to the “whole body”. Dosimeters may also be worn on the extremities or near the eye to measure equivalent dose to these tissues.

The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times. The EPDs have a top mounted display to make them easy to read when they are clipped to your breast pocket. The digital display gives both dose and dose rate information usually in mSv and mSv/h. The EPD has a dose rate alarm, and a dose alarm. These alarms are programmable. Different alarms can be set for different activities.

For example:

• dose rate alarm at 100 μSv/h,
• dose alarm: 100 μSv.

Advantages and Disadvantages of Electronic Personal Dosimeters

Advantages of Electronic Personal Dosimeters

• EPDs are able to display a direct reading of the detected dose and dose rate in real time.
• EPDs have a dose rate alarm, and a dose alarm, which can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded.
• The dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times.
• EPDs are capable of measuring a wide radiation dose range from routine (μSv) levels to emergency levels (hundreds mSv or units of Sieverts) with high precision

Disadvantages of Electronic Personal Dosimeters

• EPDs are generally the most expensive dosimeters.
• EPDs are generally large in size.
• EPDs are used to measure and record radiation exposure due to gamma rays, X-rays, sometimes beta particles. For neutrons, TLDs are more capable.

DIS Dosimeter

Direct-ion storage dosimeter, DIS, is an electronic dosimeter, from which the dose information for both Hp(10) and Hp(0.07) can be obtained instantly at the workplace by using an electronic reader unit. The DIS dosimeter is based on the combination of an ion chamber and a non-volatile electronic charge storage element.

DIS dosimeter use an analog memory cell inside a small, gas-filled, ionization chamber. Incident radiation causes ionizations in the chamber wall and in the gas, and the charge is stored for subsequent readout. The DIS dosimeter is read at the user’s site through connection to an electronic reader unit. The DIS dosimeter is designed to clip to a breast pocket. The DIS series of personal electronic radiation dosimeters can operate at high dose rates and inside pulsed fields. It’s lightweight, but rugged. The DIS dosimeter represents a potential alternative for replacing the existing film and thermoluminescence dosimeters (TLDs) used in occupational monitoring due to its ease of use and low operating costs.

See also:

EPD