New Measurements of the Helium-3 and Helium-4 Contents of Meteorites
Abstract
3 and Helium-4 Contents of Meteorites. C~RL A. BAUER, The Pennsylvania State University, University Park, Pennsylvania. Forty-nine measurements of the helium contents of 31 metallic meteorites were made with the special mass spectrometer at the University of Minnesota. It is a double-focusing mass spectrometer (Hoffman and Nier, 1958, Phys. Rev. 112, 2122) that was especially designed and constructed for simultaneously measuring the helium-3 and helium-4 in gas samples. Utie specific ~im was to determiiie the rai~ge iii the helium contents better and the ratio of helium-3 to helium-4 existing in metallic meteorites. Two of the meteorites selected for this study showed helium contents far above that of any of the few previously measured for both isotopes separately or of the approximately 60 measured for total helium. Deep Springs has a total helium content about 1.7 times and Clark County about 1.4 times greater than Morden, the metallic meteorite that previously had the greatest known helium content. The ratio of helium-3 to helium-4 in Deep Springs and Clark County are 0.27 and 0.25, respectively. Since these values are not particularly high these meteorites must have had moderate amounts of shielding and thus their exposure ages must be long. The preliminary estimates of their exposure ages is of the order of 3.5 and 5.5 billion years, respectively, which is considerably longer than the 2.4 billion years found for Williamstown (Schaeffer, 1960, Phys. Today, 13,18). The helium contents of the nickel-rich ataxites are distributed much like that of the medium octahedrites. However, the hexahedrites investigated are distinct from other classes of meteorites in that their helium contents are unusually low and also their helium-3 to helium-4 ratios average much lower than other meteorites, ranging from 0.07 to 0.24. This is important because it indicates, for the first time, that these meteorites, as a class, have had a very different exposure history from other classes. This work was supported by a grant from the National Aeronautics and Space Administration.
- Publication:
-
The Astronomical Journal
- Pub Date:
- 1960
- DOI:
- 10.1086/108146
- Bibcode:
- 1960AJ.....65S.340B