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

Geochronometria

Ashok Kumar Singhvi¹  Rabiul Haque Biswas¹ 

[1] Physical Research Laboratory

关键词: TL of chondrules;    anomalous fading;    degree of crystallinity;    thermal metamorphism;    thermal annealing;   

DOI  :  10.2478/s13386-013-0114-9

学科分类：社会科学、人文和艺术（综合）

来源: Politechnika Slaska * Instytut Fizyki

【 摘 要 】

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.

【 授权许可】

Unknown