Red and blue colouration of thermoluminescence from natural quartz sands

Abstract

Abstract Quartz extracts, from a pegmatite rock, volcanic ashes and beach sands, were exposed to X-rays or gamma-rays upto 8.8 kGy (880 krad). The irradiated sands were observed through a thermoluminescence colour image technique (abbreviated to TLCI by the authors) using highly sensitive colour photographic system. Remarkably different colour images, which are readily distinguishable into red and blue TL-emitting grains on TLCI, were observed among the geologically different quartz sand varieties. The quartz sands from volcanic ash layers, containing β-quartz (mineralized at high temperature), always indicate a red TLCI, whereas the quartz rocks from pegmatite origin and granite strata, containing α-quartz (mineralized at low temperature), gave a typical blue TLCI, being consistent with the well known quartz TL colour. Quartz fractions from the beach sands showed a mixture of both red and blue TLCI, probably reflecting the respective mixtures of β-(in their origin) and α-quartz fractions along the riverside area. The search using X-ray diffractometry and instrumental neutron activation analysis proved that the cause of distinctly different colourations was attributable to the impurity atoms: light rare earth elements (Eu and/or Sm) bringing on red TLCI, while structural defects yielding the blue TLCI.