Thermoluminescence and electron paramagnetic resonance study on black obsidian from Mt. Ağrı

This study investigates the thermoluminescence (TL) and electron paramagnetic resonance (EPR) properties of black obsidian, collected from the foothills of Mt. Ağrı, for radiation measurement applications. Various grain sizes were prepared to examine their effect on TL and EPR signal quality. Structural and elemental analyses were performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) spectroscopy. EPR analysis identified a broad signal at g=2.23, attributed to Fe3+ clusters or magnetic inclusions, and a secondary signal at g=4.89, corresponding to single Fe3+ ions. The optimal grain size for EPR was found to be 125–250 μm, which exhibited a more linear response to microwave power. For TL, a distinct peak at 100 °C and another at 305 °C were observed across all grain sizes. The best grain size for TL measurements was ≤63 μm, providing a sharper, more intense peak at the dosimetric part of the spectrum. The TL dose response ranged from 0.0625 to 200 Gy, exhibiting both super-linear and sub-linear behaviors, with a minimum detectable dose (MDD) of 44.06 ± 8.89 mGy. Kinetic analysis via the Tmax−Tstop experiment revealed multiple peaks corresponding to different energy levels, and deconvolution using general order kinetics yielded activation energies from 0.89 to 1.84 eV, with good agreement between experimental and theoretical results. Reusability tests showed minimal signal variation, confirming the material's stability for repeated use. These findings suggest black obsidian's potential for environmental and personnel radiation monitoring, particularly for low-dose applications, with further exploration needed under various radiation conditions for broader dosimetric use. The combined use of TL and EPR techniques enhances its suitability for comprehensive radiation monitoring.