科研之友
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摘要
The gamma-ray activities of 33 meteorite samples (30 ordinary chondrites, 1 Mars meteorite, 1 iron, 1 howardite) collected during Omani-Swiss meteorite search campaigns 2001-2008 were nondestructively measured using an ultralow background gamma-ray detector. The results provide several types of information: Potassium and thorium concentrations were found to range within typical values for the meteorite types. Similar mean Al-26 activities in groups of ordinary chondrites with (1) weathering degrees W0-1 and low C-14 terrestrial age and (2) weathering degree W3-4 and high C-14 terrestrial age are mostly consistent with activities observed in recent falls. The older group shows no significant depletion in Al-26. Among the least weathered samples, one meteorite (SaU 424) was found to contain detectable Na-22 identifying it as a recent fall close to the year 2000. Based on an estimate of the surface area searched, the corresponding fall rate is similar to 120 events/10(6)km(2)*a, consistent with other estimations. Twelve samples from the large JaH 091 strewn field (total mass similar to 4.5t) show significant variations of Al-26 activities, including the highest values measured, consistent with a meteoroid radius of similar to 115cm. Activities of U-238 daughter elements demonstrate terrestrial contamination with Ra-226 and possible loss of Rn-222. Recent contamination with small amounts of Cs-137 is ubiquitous. We conclude that gamma-ray spectroscopy of a selection of meteorites with low degrees of weathering is particularly useful to detect recent falls among meteorites collected in hot deserts.
- 出版日期2017-6
