Title: Mass Spectrometrical Study of Rare Gas Compositions and Neutron Capture Effects in Yamato-74191 (L 3) Chondrite
Abstract: Abstract The unequilibrated hypersthene chondrite Yamato-74191 was studied mass spectrometrically for rare gases released at various temperatures. Cosmogenic gases dominate in He and Ne. The meteorite contains large amounts of trapped Ar, Kr and Xe, and radiogenic 40 Ar and 129 Xe. Cosmic-ray irradiation and K-Ar ages were determined. In addition to spallogenic components of Kr and Xe, isotopic excesses of 80 Kr, 82 Kr, 128 Xe and 126 Xe relative to AVCC-Kr and -Xe were found. The ratio of 80 Kr-excess to 82 Kr-excess is 2.66 after correction for spallogenic Kr. A correlation between 128 Xe/ 132 Xe and 129 Xe/ 132 Xe was found The 129 Xe/ 132 Xe ratio for trapped Xe in Yamato-74191 was determined as 1.12 ± 0.29 with the correlation plot. The excesses found in Yamato-74191 are best explained by epithermal neutron capture on Br and I, and by the 127 I (n, 2nβ) 126 Xe reaction. Using neutron-produced 80 Kr, the neutron slowing -down density was estimated to be 0.14 ± 0.03 cm -3 sec -1 . A minimum mass and a preatmospheric radius was estimated to be 470 kg and 32 cm, respectively.