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Types of Personal Dosimeters

Personal dosimeters are devices that workers exposed to radioactive materials wear. Except for the self-reading type, dosimeters are intended to measure cumulative exposure. After workers wear a dosimeter for a specified time, they analyze it and report the cumulative exposure. Radiation exposure is not uniform, so workers may wear the dosimeter on their chest, their waist or on a finger depending on which is nearer the radiation source.

  1. Film Badges

    • Film badges use radiation sensitive film as detectors. The film is also sensitive to light, moisture, heat and certain chemicals; workers must seal it in a container, which prevents them from exposing it to any of these stimuli. Workers must place the film behind a series of filters, which makes it possible to determine the kind of radiation that the worker has been exposed to. Film badges are the least accurate of the dosimeters at low levels of radiation, and their sensitivity to heat makes them impractical for many applications.

    Optically Stimulated Luminescent

    • To be effective, workers must wear the dosimeter outside of their protective clothing.

      In optically stimulated luminescent (OSL) dosimeters, aluminum oxide crystals are the detectors, and their luminescent properties are altered by exposure to radiation. After workers wear them for a specified period, they can stimulate the crystals using a green light from a laser or LED; the intensity of blue light that the crystals emit is proportional to the amount of exposure. OSL dosimeters are much more accurate than film badges and can measure exposure at very low levels. OSL dosimeters are more environmentally stable than film badges.

    Thermoluminescent

    • The thermoluminescent dosimeter (TLD) uses a phosphor such as lithium fluoride as a detector. When exposed to radiation, free electrons are released and trapped in the crystal structure of the phosphor. When the phosphor is heated, the electrons are freed and give off energy in the form of light. The amount of light released is a measure of radiation exposure. TLDs are only slightly more accurate than film badges at low levels of radiation. TLDs are impervious to heat and moisture.

    Pocket

    • The pocket dosimeter, or self-reading dosimeter, is pen-shaped and indicates real-time radiation exposure. It contains a quartz fiber that the electric field around it can deflect. Exposure to radiation affects the strength of the field, and the amount of the fiber's deflection can determine the real-time level of radiation.

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