* Astronomy

Title: Fall, classification and cosmogenic records ofthe Sabrum (LL6) chondrite
Authors: S. GHOSH, S. V. S. MURTY, P. N. SHUKLA, A. D. SHUKLA, R. R. MAHAJAN, N. BHANDARJ, N. C. PANT, I. B. GHOSH AND S. SHOME

The petrographic and chemical characteristics of a fresh Indian meteorite fall at Sabrum are described. Its mean mineral composition is defined by olivine (Fa31.4), orthopyroxene (Fs25.1,Wo2.0), clinopyroxene (Wo45En45.6Fs9.4) and plagioclase (An10.6Ab83.6Or5.8). The meteorite shows moderate shock features, which indicate that it belongs to the S4 category. Based on mineralogical and chemical criteria the meteorite is classified as an LL6 brecciated veined chondrite. Several cosmogenic radioisotopes (46Sc, 7Be, S4Mn, 22Na and 26Al), noble gas (He, Ne, Ar, Kr and Xe), nitrogen isotopes, and particle tracks density have been measured. Concentrations of cosmogenic 21Ne and 38Ar indicate that its cosmic-ray exposure age is 24.8 Ma. Small amounts of trapped Kr and Xe, consistent with petrologic class 5/6, are present. The track density in olivines is found to be (1.3 ± 0.3) x 106/cm². Activities of most of the short-lived isotopes are lower than those expected from solar cycle variation. 22Na/26Al (1.12 ± 0.02) is found to be significantly anomalous, being 25% lower than expected from the Climax neutron monitor data. These results indicate that the cosmic-ray flux during the terminal segment of the meteoroid orbit was low. The activities of26Al and 60Co and the track density indicate small meteoroid size with a radius 15 cm.

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