Radionuclide activities in recent chondrite falls determined by gamma‐ray spectrometry: Implications for terrestrial age estimates

Rosén, Åke V.; Hofmann, Beda A.; Sivers, Moritz; Schumann, Marc (2020). Radionuclide activities in recent chondrite falls determined by gamma‐ray spectrometry: Implications for terrestrial age estimates. Meteoritics & planetary science, 55(1), pp. 149-163. Meteoritical Society at the University of Arkansas, Dept. of Chemistry and Biochemistry 10.1111/maps.13427

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Radionuclide activities were measured in the low-background gamma-ray
spectrometry facility GeMSE in eight meteorite falls (Lost City, Tamdakht, Huaxi,
Boumdeid, Xining, Kamargaon, Degtevo, and Ouidiyat Sbaa) and two finds (SaU 606 and Mürtschenstock) to evaluate the use of radionuclides for terrestrial age estimates. Results indicate that these meteorites were all derived from small- (r < 25 cm) to medium-sized (r < 65 cm) meteoroids. Short-lived 48V (t1/2 = 16.0 d) and 51Cr (t1/2 = 27.7 d) were only detected in Oudiyat Sbaa (EH), while 7Be (t1/2 = 53.1 d) was also detected in Degtevo (H) and Kamargaon (L), in agreement with reported fall dates. The 22Na/26Al activity ratio in Huaxi agrees with the previously reported short cosmic-ray exposure age of this meteorite while 22Na/26Al in Kamargaon likely records a complex exposure history. Bayesian statistical analysis verifies the detection of very low activities of 44Ti (t1/2 = 60 a) in the relatively large H chondrites (>100 g) Degtevo, Huaxi, Tamdakht, Lost City, and SaU 606. Additionally, large samples from Oudiyat Sbaa (EH) and Kamargaon (L) gave positive detections. For H chondrite target compositions, detected 44Ti(Fe+Ni)/26Al averaged 0.055 _ 0.013. Activities of 22Na and 54Mn in SaU 606 show that this meteorite fell between July and September 2012, making SaU 606 the second recent fall from Oman identified using gamma-ray spectrometry. The upper activity limit of 22Na in the Mürtschenstock meteorite shows that it fell prior to 1999 and is not related to a bolide observation in 2015. Mürtschenstock shows 137Cs ~109 higher than previously determined in Oman meteorites, likely due to Chernobyl fallout.

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