The Three (3) Personnel Monitoring Devices
- Refers to procedures instituted to estimate the amount of radiation received by individuals who work in a radiation environment
- Personnel monitoring device simply measures the quantity of radiation to which the monitor was exposed and therefore is used as an indicator of the exposure of the wearer
1. Film Badges
- Film badges came into general use during the mid 1940’s
- Film badges are specially designed devices in which a small piece of film similar to dental radiographic film is sandwiched between metal filters inside a plastic holder
- The film incorporated into a film badge is special radiation dosimetery film that is particularly sensitive to ionizing radiation
- Exposure less than 10 mR (2.6 µC/Kg) are not measured by film badge monitors
- Film badge cannot be worn for long periods because of fogging cause by temperature and humidity
- Film badge monitors should be not worn for longer than 1 month
2. Thermoluminescence dosimeters (TLD’s) or OSL Dosimeter
- Lithium Flouride (LiF) in crystalline from – is the sensitive material of the TLD monitor
- When exposed to x-rays, the TLD absorbs energy and stores it in the form of excited electrons fall back to their normal orbital state with the emission of visible light
- Intensity of visible light – is measured with the photomultiplier tube (PM) and is proportional to the radiation dose receive by the crystal
- TLD monitoring device is more sensitive and more accurate than the film badge monitor
- TLD monitors can be worn for intervals up to 3 months at a time
- Optically Stimulated Luminescent Dosimeter method makes use of electrons trapped between the valence and conduction bands in the crystalline structure of certain types of matter (such as quartz, feldspar, and aluminum oxide).
- The ionizing radiation produces electron-hole pairs
- The electrons which have been excited to the conduction band may become entrapped in the electron or hole traps.
- Under stimulation of light the electrons may free themselves from the trap and get into the conduction band.
- From the conduction band they may recombine with holes trapped in hole traps. If the center with the hole is a luminescence center emission of light will occur.
- The photons are detected using a photomultiplier tube.
- The signal from the tube is then used to calculate the dose that the material had absorbed.
- The OSL dosimeter provides accurate reading as low as 1 mrem for x-ray and gamma ray photons with energies ranging from 5 keV to greater than 40 MeV.
3. Pocket ionization chamber
- Pocket ionization chambers are small devices measuring approximately 2cm by 10cm long and are designed to be clipped onto a wearing apparel
- Pocket ionization chamber that are usually use is diagnostic imaging has a range of 0 to 200 mR (0 to 50 µC/Kg)