Helium,neon, and argon in the iron meteorites Dongling,Nantan and Ningbo |
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Authors: | H W Weber O Braun F Begemann |
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Institution: | 1. Max-Planck-Institut für Chemie, Saarstra?e 23, D-6500, Mainz, F.R.G.
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Abstract: | The light noble gases He, Ne and Ar have been measured in the iron meteorites Dongling, Nantan and Ningbo. Dongling and Ningbo
show a deficit of cosmic-ray that produced3He of ca. 30% and 10%, respectively, which is argued to be caused by the loss of3H (tritium) from the meteoroids during the time of their exposure to the cosmic radiation. Nantan has the lowest content of
noble gases as yet reported for any iron meteorite. Cosmogenic3He and38Ar are only about 1/5000 of those in Dongling which has particularly interesting implications if the two meteorites belong
to the same fall2]. In addition, Nantan contains nonspallogenic4He which we believe to be of radiogenic origin. This radiogenic4He, together with a U-content of 2.6×10−11 g/g20] yields a4He retention age close to the cosmic-ray exposure age of Dongling. If Dongling and Nantan were part of the same meteoroid2], this result would indicate that He retention in the meteoroid age were 4,500 Ma, a U-content of less than 7.2×10−13 g/g is required to explain the non-cosmogenic4He present. An upper limit to the number of transuranium or superheavy-element atoms which have decayed by α-emission in Nantan
since onset of He retention is 2×1010 per gram. |
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