It also contains three small metallic filters - usually copper, cadmium, and aluminum - placed in different portions of the case to help distinguish among higher energy photons. Each of the metals attenuates photons of different energy values. In summary, this packaging has been devised so that the film badge can measure the air kerma which the wearer has encountered and can also help distinguish the type of radiation to which he or she has been exposed. The outside of the film wrapper has the name, date of issue, and identification number of the wearer imprinted on it.
Film badges are a popular personnel monitoring device because they provide a permanent record of each individual's accumulated exposure. They are also inexpensive and require no technical knowledge to the user.
These personnel monitors can be used in the same way as film badges. They are common for whole-body monitoring as well as for special types of monitoring, such as monitoring the hands for radiation. Since they may be affixed anywhere in the treatment field and may be attached directly to a patient, they are often used in radiation oncology applications in particular to verify the treatment plan.
Substance that posses the property of thermoluminescence are nonmetallic crystalline solids, usually in powdered form. When electrons in a crystal insulator absorb energy, they move to the higher energy conduction band and all the missing electrons or holes migrate to the valence band. In a thermoluminescent crystal, these excited electrons get trapped in the higher energy state until the crystal is heated to a specific temperature, known as the curie temperature, at which the electrons return to the valence state, radiating the extra energy in the form of visible light photons. Lithium fluoride, lithium tetraborate, and manganese-activated calcium fluoride are crystals commonly used for their thermoluminescent properties. The curie temperature of these substances is 845, 930 and 1423C respectively.
c. Ion-Chamber Personnel Monitors
Ion-chamber monitors have been designed so that air kerma levels can be read at any time, either by the user or some other designated person. These simple ion-chamber monitors are shaped like a large fountain pen and attach to the clothing. As with other ionization chambers, these monitors must be calibrated for the energy range of the radiation to be monitored as well for permissible amount of charge leakage per week for the chamber to remain in calibration. Two kinds of ion-chamber monitors are available. One is known as direct-reading pocket monitor, because the person using it can read it at any time. The other is a condenser-type pocket chamber, which requires a separate device for both charging and obtaining results.
Both kinds of ion-chamber devices must be recharged daily since significant leakage of charge may occur over long periods of time. Both are read immediately after use. In addition, ion-chamber monitors tend to be fragile rather than rugged. This type of monitor is also more costly than either the thermoluminescent dosimeter or the film badge, with the