The shape of the TLD-300 glow curve as a function of the energy for photons below 30 keV: Application to triboluminescence X-rays from peeling adhesive tape

Abstract

The thermoluminescent material CaF2(Tm), known as TLD-300 (Harshaw/Bicron), shows a remarkable dependence of its glow curve shape on the quality of the radiation field. The quotient of high-temperature (maximum at about 265 °C) and low-temperature peaks (maximum at about 175 °C) depends strongly on LET (ions) and photon energy. The shape of the glow curve is parameterized by the high-to-low-temperature ratio, HLTR, a decreasing function of photon energy.Our goal has been to investigate the TLD-300 glow curve shape for six photon energies between 6 and 28 keV, and to apply this extended HLTR calibration to determine the effective energy of triboluminescence-generated X-rays (TGXs) produced when peeling adhesive tape in vacuum.For calibration, TLD-300 chips were exposed to X-rays from a W-anode tube (9.7–27.7 keV effective energies), X-rays from a Cu-anode tube (8.0 keV) and a 55Fe radioactive source (5.9 keV). The chips were subjected to an annealing protocol designed to improve the stability of the low-temperature peaks. Doses were low and deconvolution into 7 peaks was performed with custom-made software. For the TGXs investigation, TLD-300 chips and TLD-100 microcubes were exposed inside a vacuum chamber to radiation generated by the peeling of adhesive tape from its own backing. The dosimeters, located at different angular positions with respect to the tape, were covered with a 21-μm thick layer of Mylar (Dupont Tejjin Films) to eliminate stray radiation and block any UV light that may be emitted along with the TGXs. TLD-300 were thermally handled as in calibration, and the HLTR indicated the effective energy. Microcubes were used as monitors of a controlled exposure.The new calibration data confirmed the previous trend and showed consistency with existing HLTR measurements above 30 keV (after correcting by the different annealing procedures). The TGXs TLD-300 glow curves showed the presence of a low-temperature peak below those included in the usual deconvolution. The measured HLTR indicated effective energies close to 7 keV and constant over a wide range of observation angles.The extended calibration validates the use of this technique to evaluate photon energies below the limits investigated previously. For the investigation of TGXs, TLDs have been used as passive dosimeters, offering new possibilities in cases where pileup would be a limiting factor for active solid-state active detectors. The difference in glow curve shapes between the TGXs and the calibration photons offers a tool for further investigation of processes induced by surface electrification.