External Dosimeter-TLD?????

Hello readers,

Have you seen this kind of items hanging or clip at yours doctors or radiation workers overall?

OR

you never notice it before?

This item actually popular among medical practitioner which called THERMOLUMINESCENT DOSIMETER  a.k.a  TLD!

I'm sure you are curious to know about it now! if NOT, Please continue reading :)

WHAT IS TLD?

It is a primary form of personnel radiation exposure monitoring which  often used instead of the film badge. Like a film badge, it is worn for a period of time (usually 3 months or less) and then must be processed to determine the dose received, if any. 

Thermoluminescent dosimeters can measure doses as low as 1 millirem, but under routine conditions their low-dose capability is approximately the same as for film badges.

Interesting right? Now you can continue reading to know more interesting facts about TLD  !

In spite of its small size, it can measure radiation dose effectively.
So, lets see how TLD works.
 

Thermoluminescent (TL) means emitting light when heated. We can briefly describe the mechanism of TL as follow: 

When a strong energy source (such as ionizing radiation) hits a TL material, electrons are freed from some atoms and moved to other parts of the material, leaving behind "holes" of positive charge. Subsequently when the TL material is heated, the electrons and the "holes" re-combine, and release the extra energy in the form of light. The light intensity can be measured, and related to the amount of energy initially absorbed through exposure to the energy source. 

Heating of the TL material causes the trapped electrons to return to the valence band. When this happens, energy is emitted in the form of visible light.

The results of a TLD measurement are interpreted by a glow curve. As electrons in the bad gap are released at varying intervals, light output intensity varies. When the light intensity is graphed, the highest peaks are used to interpret radiation dosage. Only a fraction of incident energy is absorbed by a TLD. The ratio of the thermoluminescent light emitted per unit mass over the absorbed dose is known as intrinsic efficiency.

the advantage of TLD is stated below :

• linearity of response to dose, its relative energy independence, and its sensitivity to low doses. It is also reusable, which is an advantage over film badges.
• Able to measure a greater range of doses.
•  Small in size
• Available in various forms.
• Some are reasonably tissue equivalent .
• Not expensive.
•  Reusable.

TLD also have disadvantages when comparing to other external dosimetry such as ;

• No permanent record or re-readability is provided and an immediate, on the job readout is not possible.
• Lack of uniformity
• Batch calibration needed
• Storage instability
• Fading
• Light sensitivity
• Spurious TL (cracking, contamination)  

These are interesting facts about TLD. Keep reading our blog to know more about radiation protection...