A gamma-ray spectroscopy survey of Omani meteorites

Patrick Weber, Beda A Hoffmann, Tamer Tolba, Jean-Luc Vuilleumier

submitted to Meteoritics ans Planetary Science

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“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 ultra-low 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 26Al activities in groups of ordinary chondrites with a) weathering degrees W0-1 and low 14C terrestrial age and b) weathering degree W3-4 and high 14C terrestrial age are mostly consistent with activities observed in recent falls. The older group shows no significant depletion in 26Al. Among the least weathered samples two meteorite were found to contain clearly detectable 22Na indicating they are recent falls. Based on an estimate of the surface area searched, the corresponding fall rate is <120 events/106 km2*a, consistent with estimated fall rates. 12 samples from the large JaH 091 strewn field show significant variations of 26Al activities, including the highest values measured, requiring a meteoroid radius of ~100 cm. Activities of 238U daughter elements demonstrate terrestrial contamination with 226Ra and possible partial loss of 222Rn. Recent contamination with small amounts of 137Cs is ubiquitous. We conclude that gamma-ray spectroscopy is particularly useful to detect recent falls among meteorites collected in hot deserts. "