Characterization of the natural thermoluminescence emission of lava flows

Abstract

We herein report on the natural thermoluminescence (TL) emission of eight lava flows from different volcanic regions that could potentialIy be useful for dating purposes. AH the samples were characterized by means of: (i) x-ray diffraction to determine the components that act as main contributors of the TL response and (ii) gamma-ray spectrometry to identify the natural radionuclides that induce the TL glow curve. In this sense, plagioclases (Na-Ca feldspars) are the most cornmon mineral detected in lava flows (up to 45%) just with augite (silicate with composition (Ca, Mg,Fe)2(Si,AI)2ü6) that is a part of an important so lid solution series of the pyroxene group (up to 35%). Different amounts of cristobalite, montmorillonite, forsterite, actinolite and hematite have been also identified. The level of the activity (in Bq/kg) differs from one sample to another. Thus, 238U values are in a range of 6.33 and 30.4; 232Th estimations are between 3.06 and 51.2 and 40K values between 191 and 564. The observed changes in the natural TL emission of the samples depend, essentialIy, on (i) the mineralogical composition, (ii) the elapsed time from the last eruption, i.e. when the last zeroing took place and (iii) the radioactive content. The activation energy (Ea) values have been estimated by the applicability of the initial rise method to the TL glow curve.