- EPD – Electronic Personal Dosimeter
- Characteristics of EPDs
- Advantages and Disadvantages of Electronic Personal Dosimeters
- Film Badge Dosimeter
- Advantages and Disadvantages of Film Dosimeters
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.
- 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.