Thermoluminescence dosimetric and kinetic characterization of Pakistani fluorite after β irradiation

Abstract

The thermoluminescence (TL) characteristics of seven fluorite mineral samples from Pakistan have been investigated for the first time. The TL glow curve structure of different colors of fluorite were thoroughly studied for their potential use in dosimetric applications. Light green (LG) fluorite was found the most sensitive and promising one. Therefore, light green (LG) fluorite was further investigated in detail as TL dosimeter. First, the crystallinity, microstructural properties, and potential impurities present in the LG sample were identified using x-ray powder diffraction (XRD), Scanning electron microscopy (SEM-EDX), and inductively coupled plasma (CP) techniques respectively. The β-irradiated powder sample showed that this fluorite has a complex glow curve structure with five prominent peaks at about 75, 100, 163, 251, and 358 °C in the temperature range of 40 to 400 °C. In the low β dose range of 80 mGy to 5120 mGy, the sample dose response was linear with a minimum detectable dose of 9.7 mGy. Taking the peak specific dose responses, the peak around 251 °C (R2 = 1) was found most suitable for dosimetric applications. A progressive decrease is observed in the response which reached to about 4% after 10 cycles of irradiation, readout and annealing with less than 1% coefficient of variation (COV). After one week, the TL signal faded by approximately 8%; however, after one month of storage, the signal returned to near-stable level. A newly designed deconvolution program was used for the analysis of the TL kinetics. The kinetic parameters like activation energy (E), frequency factor (s), the order of kinetics (b), and the trap lifetimes were investigated. The values found using additive dose (AD), Tm -Tstop, various heating rate (VHR) and computerized glow curve deconvolution (CGCD) methods were in close proximity. The study concludes that light green fluorite from Pakistan can be used as a potential candidate for thermoluminescence dosimetry (TLD) applications.