Radiation effects on TL and EPR of sodalite and application to dosimetry

Sodalite, Na8Al6Si6O24Cl2, a natural silicate mineral, has been investigated concerning its thermoluminescence (TL) and electron paramagnetic resonance (EPR) properties. Samples, both natural and heat treated at 500°C for 30min, present an EPR signal at g=2.01132. The irradiation induces two signals at g=2.0008 and a group of 11 lines due to an O− ion in an intermediate position with respect to two adjacent Al nuclei, that are superimposed on the signal at g=2.0008. An annealing at 500 °C/30min produces a broad signal around g~2.0, probably due to Fe3+ magnetic dipole interactions. The samples were annealed at 500 °C/30min and then irradiated with gamma-ray doses varying from 1 Gy to 20 kGy. All the samples have shown TL peaks at 110, 230 and 270 °C. Similar results were obtained for natural samples. The accumulated dose (AD) was determined to be AD~2.5 kGy and the annual dose of (0.595±0.001) mGy/year was obtained from the concentration of U, Th, and K2O in the sample. Therefore, the age obtained for natural sodalite was (4.2±0.2)106 years.