Laser heating in thermoluminescence dosimetry

Abstract

Thermoluminescence (TL) glow curves have been obtained from γ-irradiated commercial dosimetry materials (LiF:Mg, Ti; CaSO4:Mn; CaSO4:Dy; CaF2:Dy; Li2B4O7) with a novel laser heating technique. It utilizes short (10–1000 ms) pulses from a CO2 laser of 1–8 W power focused to about 1-mm diam spot sizes onto thin (<100 μm) layers of powder precipitated on microscope cover slides. In some cases these powder layers were spray coated with a thin film of conventional high temperature polymers. These acted both as a binder to stabilize the powder as well as to enhance the heat transfer from the laser beam to those TL materials which have a small absorption coefficient for 10.6 μm photons (e.g., LiF and CaF2). Heating rates in excess of 104 K s−1 have been observed without noticeable decrease in the TL emission efficiency. Laser heating is, thus, shown to be a promising technique to increase the signal-to-noise ratio of TL emission signals. As a result, true microdosimetry in the mR range could be demonstrated with samples of less than 20 μg. Applications to remote in situ TL microdosimetry can now be anticipated as well as sensitive high resolution TL imaging of spatial exposure distributions.