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Mass spectrometric ^3He measurement in ^4He-rich phases: Techniques and limitations for cosmogenic ^3He dating of zircon, apatite, and titanite
| Content Provider | Semantic Scholar |
|---|---|
| Author | Amidon, William H. Farley, Kenneth A. |
| Copyright Year | 2010 |
| Abstract | Recent calibration studies have expanded the range of target minerals suitable for cosmogenic ^3He dating to include U and Th-rich phases such as zircon, apatite, and titanite. These minerals often contain large amounts of radiogenic ^4He that present several analytical challenges for precise and accurate ^3He determinations. In this paper we document the abundance sensitivity and changes in the absolute sensitivity and time evolution of the ^3He signal over a wide range of ^4He pressures in a MAP 215-50 noble gas mass spectrometer. Large (>50%) decreases in sensitivity with ^4He amount arising from space charge effects were observed but can be corrected for using an isotope dilution–like technique in which ^3He spike is added to a sample midway through the mass spectrometric analysis. Large amounts of ^4He also cause the time evolution of the ^3He signal to become steeper, degrading precision of the initial peak height determination from the intercept. Taken together we find that these effects preclude reliable analysis of samples with ^4He > 1 μmol and that ^3He/^4He ratios of greater than ~5 × 10^(−10) are required to routinely measure ^3He to better than 20% precision. We present some general considerations by which to assess the probability of success of measuring cosmogenic ^3He in these phases as a function of elevation, exposure age, and helium cooling age. |
| File Format | PDF HTM / HTML |
| DOI | 10.1029/2010GC003178 |
| Alternate Webpage(s) | http://authors.library.caltech.edu/21528/1/Amidon2010p12305Geochem_Geophy_Geosy.pdf |
| Alternate Webpage(s) | http://community.middlebury.edu/~wamidon/pdfs/amidon_G3_2010.pdf |
| Alternate Webpage(s) | https://doi.org/10.1029/2010GC003178 |
| Volume Number | 11 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
