Use
As with other types of personal radiation dosimeter, it is worn by workers who are occupationally exposed to radiation, so their employers can keep a record of their exposure, to verify that it is below legally prescribed limits. It works by measuring the decrease in electrostatic charge on a metal conductor in an ionization chamber, due to ionization of the air in the chamber by radiation. It was invented in 1937 by Charles Lauritsen.
The dosimeter must be periodically recharged. It is usually read before it is charged, and the dose is logged, to chart one's exposure. In many organizations, possession of the recharger is limited to health physicists to prevent falsification of exposures. Magnifying lenses (a low-power microscope) and an illumination lens allow one to directly read the dose at any time by aiming the illumination lens at a light source and looking into the device.
The device is mainly sensitive to gamma and x-rays, but it also detects beta radiation above 1 MeV. Neutron sensitive versions have been made.
Quartz fiber dosimeters are made in different ranges. Peace-time occupational exposure ranges usually measure up to 500 mrem (5 mSv), which exceeds the normal US yearly dose of 360 mrem (3.6 mSv). War-time fallout meters measure up to 500 rem (5 Sv), roughly the lethal dose.
The quartz fiber device is an older dosimeter design. It suffers from these disadvantages:
- Low accuracy: Because of the analog mechanical design, accuracy is around 15%, less than other dosimeters.
- Reading errors: Since it can only be read manually it is prone to human reading errors.
- Small dynamic range: The range of the device is limited by the charge on the electrode. Once the charge is gone the device stops recording exposure. So unexpected large radiation doses can quickly saturate devices designed to monitor the more usual low level exposures.
- Susceptibility to moisture: the charging terminal is sealed with a cap, but if this should be removed during use dampness can accelerate the leakage of the charge, imitating the effect of radiation exposure. Deliberate falsification is possible, by breathing onto the exposed terminal.
Read more about this topic: Quartz Fiber Dosimeter
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