EPD – Electronic Personal Dosimeter
An electronic personal dosimeter is a modern dosimeter that can give a continuous readout of cumulative dose and current dose rate and 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 the residence time of the wearer is limited due to dose constraints.
Characteristics of EPDs
The electronic personal dosimeter, EPD, can display a direct reading of the detected dose or dose rate in real-time. Electronic dosimeters may be used as a supplemental dosimeters as well as a primary dosimeters. The passive and electronic personal dosimeters are often used together to complement each other. Dosimeters must be worn on a position of the body representative of its exposure to estimate effective doses, typically between the waist and the neck, on the front of the torso, facing the radioactive source. Dosimeters are usually worn outside 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 doses 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 easily read when 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, and 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 can 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 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 can measure 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.
- EPDs measure and record radiation exposure due to gamma rays, X-rays, and 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 measured by the TLD reader, depending on the radiation exposure. Thermoluminescent dosimeters were invented in 1954 by Professor Farrington Daniels of the University of Wisconsin-Madison. TLD dosimeters apply to situations where real-time information is not needed. Still, precise accumulated dose monitoring records are desired for comparison to field measurements or for assessing the potential for long-term health effects. In dosimetry, the quartz fiber and film badge types are superseded by TLDs and EPDs (Electronic Personal Dosimeter).
Advantages and Disadvantages of TLDs
Advantages of TLDs
- TLDs can 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 development.
- TLDs are easily reusable.
Disadvantages of TLDs
- Each dose cannot be read out more than once.
- The readout process effectively “zeroes” the TLD.