Verification of the PTOSL signal from radiation detectors using a 60Co beam and UV light from LEDs

Abstract

Radiation processing techniques induce physical, chemical and biological changes in the structures of materials, instruments and food to reach a certain desired benefit. For this reason, the systematic and periodic radiation dosimetry is so essential to determine the absorbed dose of radiation sources. If the absorbed dose applied to the materials does not correspond to the desired one, the effects in their structures can be adverse. Solid state dosimeters are radiation detectors that are already well established in routine procedures and described in the literature for gamma radiation dosimetry, such as 60Co, with beams employed em radiation processing. This work aims to study the response of commercial dosimeters based in their luminescence phenomenon using the optically stimulated luminescence (OSL) technique. Then, it seeks to verify the phototransfer effect presented by the dosimeters employing the phototransferred OSL technique (PTOSL), for further analysis of the possibility of applying these materials and these techniques for 60Co beam dosimetry. In this work, the OSL/PTOSL responses of LiF:Mg,Ti (TLD-100), CaF2:Dy (TLD-200), CaF2:Mn (TLD-400) and CaSO4:Dy (TLD-900) commercial dosimeters were studied in three steps: 1) OSL after irradiation; 2) OSL after irradiation + thermal treatment post-irradiation (TTPI); 3) PTOSL after irradiation + TTPI + illumination with UV of light-emitting diodes (LEDs). The irradiations were carried out with a 60Co beam from a Gamma-Cell system (383.65 Gy/h - October/2022). All the measurements were taken using the Risø reader system, model TL/OSL-DA-20, and with an illumination time of 100 s. The first phase was to irradiate the dosimeters with the following absorbed doses: 0.7 Gy (TLD-100 and -900), 20 Gy (TLD-200) and 50 Gy (TLD-900), and to measure the OSL signal. The values of the initial decay of the OSL curves were about 3x103 counts (TLD-100), 1x103 counts (TLD-200), 5.4x103 counts (TLD-400) and 9.5.102 counts (TLD-900). For the second phase, the pellets were initially irradiated with the same doses previously given and submitted to the TTPI of 280°C/15 min (TLD-100 e -900), 250°C/15 min (TLD-200) e 350°C/15 min (TLD-400); the first point of the OSL signal was observed at about 400 counts (TLD-100), 460 counts (TLD-200), 530 counts (TLD-400) and 660 counts (TLD-900). In the third phase, the dosimeters were irradiated, treated with TTPI and illuminated with UV of 265 nm/10 min (TLD-100) and 365 nm/10 min (TLD-200, -400 and -900). Comparing these last results with those from the second step, it was possible to observe PTOSL for TLD-100 and -900, because an increase in the signal intensity was observed for both materials. For TLD-200 and -400, the signals were similar for the second and third steps, but more studies are necessary for a final conclusion.