Question

TLD Response & Annealing.
(i) Explain the physics of superlinearity of TLD detectors. For which absorbed dose is
superlinearity correction essential?
(ii) Based on the mathematical expression for the glow curve, explain the changing of
the position of the glow peaks vs heating rate

Answer 1

1. Superlinearity of TLD

The calibration factor employed to calculate the dose should not vary with the magnitude of the dose.

Expressed another way, we want the intensity of the light emitted by a TL material to be linearly related to dose, i.e., doubling the dose doubles the light out put.

At low doses, this is always the case. Unfortunately, the light output per unit dose can increase when doses above a certain magnitude are exceeded.

Supralinearity refers to this increase in light output per unit dose.

If the dose to a TL material exceeds that at which supralinearity occurs, the dose will be overestimated (assuming the calibration factor was determined at a lower dose in the linear region).

The higher the dose at which suprerlinearity begins, the better.

LiF is the worst TL material in terms of superlinearity. The onset of superlinearity with LiF is just above 1 Gy (100 rads). For this reason, LiF is sometimes paired wit h Li₂B₄O₇ for which superlinearity doesn’t begin until 300 rads or so.