A dosimeter is a device used to detect the levels of exposure to ionizing radiation. Dosimeters range from large laboratory devices to small personal dosimeters worn on the body. Dosimeters are frequently used in environments where exposure to radiation may occur, such as nuclear power plants and medical imaging facilities. Emergency responders may also use dosimeters, particularly when responding to emergencies involving radioactive materials.
Quartz Fiber Dosimeter
A quartz fiber dosimeter, also known as a quartz fiber and electroscope, consists of a tiny ionization chamber that contains a small quartz fiber. The chamber and fiber are contained in a metal tube with a lens that allows the fiber to be viewed. When exposed to radiation, the quartz fiber is deflected. When viewed through the eyepiece lens, this deflection can be easily seen against a scale. A disadvantage of quartz fiber dosimeters is that they can be easily damaged if handled improperly or dropped.
Film Badge Dosimeter
An inexpensive form of personal dosimeter, film badge dosimeters use a highly sensitive form of silver halide photographic film, placed inside a small case that can be worn on the body. With an array of filters inside, these dosimeters can detect exposure to beta, gamma, X-ray and thermal radiation. To check the dosimeter, the film is first removed then developed and compared to a calibrated film to determine the level and type of exposure. The film, in turn, can be used as a permanent record of an individual's exposure. This type of dosimeter does require darkroom facilities and has a relatively short shelf life.
Thermoluminescent Dosimeter
Thermoluminescent dosimeters, or TLDs, use thermoluminescent materials to detect radiation. These materials trap electrons. To read the dosage, the TLD is heated, which causes it to generate light that can be read by electronic equipment to determine the level of dosage. Different types of TLDs are available. Lithium-based TLDs are used for personal dosimetry because of the exposure similarities to that of human tissue. Calcium-based TLDs are used for environmental monitoring because of their high level of sensitivity. Lithium borate TLDs are capable of detecting extremely high levels of exposure. A special device is required to heat and read the TLD, which can then be reused.
Electronic Dosimeter
Electronic dosimeters use silicon diodes, metal-oxide semiconductor field effect transistors, or even diamonds to detect levels of ionizing radiation. These devices are extremely sensitive and can cover the full spectrum of photons and electrons. These can range from large laboratory units to small hand-held units that can be used easily in the field. Electronic dosimeters provide real-time readouts of exposure.
SIRAD
SIRAD, an acronym for self-indicating instant radiation alert and dosimeter, is one of the latest types of dosimeters to be developed. Made of plastic and about the size of a credit card, a SIRAD can be easily worn and is relatively inexpensive, costing between $10 and $20. Upon exposure to ionizing radiation, the center section of the badge will change colors and can be compared to a color chart on the dosimeter.
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