R.H. Biswas

Anomalous fading and crystalline structure: Studies on individual chondrules from the same parent body

Plagioclase feldspar is the major luminescent mineral in meteorites. Thermoluminescence (TL) characteristics, peak temperature (Tm), full width at half maximum (FWHM), ratio of high (HT) to low temperature (LT) peak, and TL sensitivity (TL/dose/mass) to an extent reflect degree of crystallinity of the mineral. The present study explores and establishes a correlation between quantum mechanical anomalous (athermal) fading and structural state by examining TL of individual chondrules. Chondrules were separated using freeze-thaw technique from a single fragment of Dhajala meteorite. The results show large variation in Tm (155−230°C), FWHM (80−210°C) and HT/LT (0.07–0.47) and seem to be positively correlated. TL sensitivity (ranging from 14 to 554 counts/s/Gy/mg) decreases with increasing Tm and FWHM. Large variations in TL parameters (Tm, FWHM, HT/LT, and Sensitivty) suggest that individual chondrules had different degree of crystallization. Thermal annealing experiments suggest that comparatively ordered form of feldspar can be converted to a disordered form by annealing the sample at high temperatures (1000°C) for long time (10 hr) in vacuum (1 mbar pressure) condition and rapidly cooling it. Measured anomalous fading suggest that fading rate increases as the crystal form changes from an ordered state to a disordered state. However, the fading rate becomes nearly negligible for the most disordered feldspars.

Development and Application of Luminescence to Earth and Planetary Sciences: Some Landmarks

Luminescence, mainly thermoluminescence (TL) and optically stimulated luminescence (OSL), has been researched for more than five decades towards its application to earth and planetary sciences. Luminescence production mechanism has been understood through several theoretical studies, like analytical kinetic theory, numerical models along with the experimental results. Instrument development has progressed with aim from user friendly TL/OSL reader dedicated for dating to challenging reader for in-situ Martian sediment dating. Since the development of optical dating in 1985, the technique revolutionised the research in earth sciences. And since then to recent, many methodologies have been developed and some are in developing stage using different signals, like, single grain OSL, red TL, time resolved OSL, thermally transferred OSL (TT-OSL), post infrared-infrared stimulated luminescence (pIR-IRSL), violet light stimulated luminescence (VSL), infrared radioluminescence (IRRL), etc. with an objective to improve the accuracy and precision and to extend the dating range. The wide range of application in different environment, e.g. aeolian, fluvial, marine, glacier, soil, volcanic materials, heated materials, shocked materials, meteorites, etc. have made the technique successful to understand the quaternary history of earth and planetary information like terrestrial and cosmic ray exposure ages of meteorite, meteoroid orbit, thermal metamorphism history of meteorite etc. The aim of this present paper is to discuss some landmarks and recent trends in the development and application in these areas. Contents of the Paper