Advanced Physics for Brachytherapy 2018

TLD: basic principles •

In imperfect crystals (i.e. TLD100: LiF doped with Mg and Ti in trace amounts) part of the energy absorbed by ionising radiation is stored and re-emitted upon heating in the form of light. Light is detected and correlated to the absorbed dose. • Stored energy is in the form of the fraction of e - freed by irradiation, that is trapped in a metastable energy state. • When the crystal is heated, part of these e - recombine with holes trapped in luminescence centers and emit light (thermo- luminescence, TL) • The curve of TL output versus temperature (glow curve) shows peaks characteristic of trap energy depths in the crystal • Besides TL crystal, glow curve shape varies with heating rate & max temperature

Figures from: Attix: Introduction to radiological physics and radiation dosimetry, © 2004 by Wiley-VCH Verlag GmbH & Co Mayles, Nahum, Rosenwald (Eds): Handbook of radiotherapy physics: theory and practice, © 2007 by Taylor & Francis Group LLC Rogers & Cygler (Eds), Clinical dosimetry measurements in radiotherapy (2009 AAPM Summer School), Monograph No. 34, Medical Physics Publishing 2011