TLD BADGE
The full form of
TLD badge is thermo luminescent dosimeter and it is used as Personnel
Monitoring Device. It measures X, 𝜷, 𝛄 radiation dose
of an individual.Generally TLD Badge
consists of a plastic cassette with a nickel coated aluminum card. This card
has three CaSO4: Dy-Teflon disks 0.8 mm thick and 13.2 mm diameter.
These discs are
mechanically clipped on three 12mm diameter circular holes on the card. The
dimensions of the Al card are 52.5 mm X29.9 mm X 1 mm. There is a V shaped cut
on the top end of the card so that these cards are always in a fixed
orientation in the cassette.
The paper of the card remains
locked in the wrapper, on which the user's personal data and the period to use
it are written. The thickness of the wrapper is 12mg / cm2, which denotes the
10mm depth below the skin surface. TLD disks are sealed in a thin polythene
pouch with wrappers to avoid damage during incorrect use. Pouch cards protect
against radioactive contamination when working with open radioactive sources.
TLD cassettes are made of high impact plastic.
It consists of three filters which are placed in front of each disk. Whose
names are Cu + Al, Perspex and open respectively. These filters are mounted on
the cassette both front and back of the card. The Cu + Al filter contains 1mm
Al and 0.9 Cu. Cu filters are towards TLD disks and Al filters are towards
radiation source. The second disc is sandwiched between 1.5mm thick
plastic filters. Its density is 180mg / cm2. The third disc is placed between
two circular open windows. The TLD discs are radiation recording device which
are sensitive to X-rays, 𝛄 –rays, 𝜷-rays there is a clip on the cassette which attaches it to the user's clothes.
Metallic filters are used
to measure X-rays and gamma rays. Perspex is for measuring beta radiation. When
TLD disks are exposed, the electrons of the crystal lattice get excited and
move from the valance band to the conduction band. Where they are trapped under
the conduction band. The number of trapped electrons is proportional to the
number of incident X-ray photons. In this way these electrons store the
absorbed energy in the crystal lattice.
The TLD card used in
the range of 10mr to 10,000mr.TLD badge service is conducted on quartly basis
and they are sent to BARC (Bhabha Atomic Research Centre) for dose evaluation
Advantage of TLD badge:-
- Fast reading capabilities for emergency situation
- Serve as dosimeter system for monitoring patient exposure and making other exposure measurements
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