Characteristics of TLDs

 

The TLDs have advantages which are listed below:

1. Gamma dose measurement over a very wide range is possible. Response  is linear between and .
2. High sensitivity, that is high light output for a given exposure, means the dosimeter  can be made small and convenient to wear.
3. They can be used to measure dose over a long period (months or even a year) with very little fading.
4. The light output is a linear function of the absorbed dose which makes calibration easy.
5. LiF is a reasonably good tissue equivalent  for beta and gamma radiation  . (This is not true for neutrons . LiF output is very dependent on neutron energy).
6. Can distinguish between types of radiation by using different lithium isotopes as will be discussed below.

The disadvantages of TLDs  are listed below.

1. The process of reading out eliminates the dose effect, so it can only be done once.
2. Since it is not possible to tell whether or not the TLD has absorbed a dose, all TLDs must be read and annealed each monitoring period.
3. Dust on the detector will glow when heated and will be recorded by the phototube as a false reading.
4. The TLDs are sensitive  to exposure by ultraviolet light and therefore must be sealed in a light-tight badge.