A gamma-ray spectroscopy survey of Omani meteorites

TL;DR

This study used gamma-ray spectroscopy to analyze 33 meteorites from Oman, revealing information about their composition, weathering, terrestrial age, and recent falls, demonstrating the method's effectiveness in identifying recent meteorite arrivals.

Contribution

The paper presents the first gamma-ray spectroscopy survey of Omani meteorites, providing insights into their terrestrial ages, weathering states, and recent fall detection, which was not previously documented.

Findings

Potassium and thorium levels within typical ranges for meteorite types.

Detection of a recent fall (SaU 424) via 22Na activity.

Estimated fall rate of ~120 events per million km² per year.

Abstract

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 one meteorite (SaU 424) was found to contain detectable 22Na identifying it as recent fall close to the year 2000. Based on an estimate of the surface area searched, the corresponding fall rate is ~120 events/106 km2*a, consistent with other estimations. Twelve samples from the large JaH 091 strewn field (total mass ~4.5 t) show significant variations of 26Al activities, including the highest values measured, consistent with a meteoroid radius of ~115 cm. Activities of 238U daughter elements demonstrate terrestrial contamination with 226Ra and possible loss of 222Rn. Recent contamination with small amounts of 137Cs 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.