Absolute isotopic composition of molybdenum and the solar abundances of the p-process nuclides {sup 92,94}Mo
- Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, T2N 1N4 (Canada)
- Department of Applied Physics, Curtin University of Technology, GPO Box U1987, Perth 6845 (Australia)
The isotopic composition of molybdenum has been measured with high precision using a thermal ionization mass spectrometer, the linearity of which has been verified by measuring the isotopically-certified reference material for strontium (NIST 987). The abundance sensitivity of the mass spectrometer in the vicinity of the molybdenum ion beams has been carefully examined to ensure the absence of tailing effects. Particular care was given to ensuring that potential isobaric interferences from zirconium and ruthenium did not affect the measurement of the isotopic composition of molybdenum. Gravimetric mixtures of two isotopically enriched isotopes, {sup 92}Mo and {sup 98}Mo, were analyzed mass spectrometrically to calibrate the mass spectrometer, in order to establish the isotope fractionation of the spectrometer for the molybdenum isotopes. This enabled the ''absolute'' isotopic composition of molybdenum to be determined. An accurate determination of the isotopic composition is required in order to calculate the atomic weight of molybdenum, which is one of the least accurately known values of all the elements. The absolute isotope abundances (in atom %) of molybdenum measured in this experiment are as follows: {sup 92}Mo=14.5246{+-}0.0015; {sup 94}Mo=9.1514{+-}0.0074; {sup 95}Mo=15.8375{+-}0.0098; {sup 96}Mo=16.672{+-}0.019; {sup 97}Mo=9.5991{+-}0.0073; {sup 98}Mo=24.391{+-}0.018; and {sup 100}Mo=9.824{+-}0.050, with uncertainties at the 1s level. These values enable an atomic weight A{sub r}(Mo) of 95.9602{+-}0.0023 (1s) to be calculated, which is slightly higher than the current Standard Atomic Weight A{sub r}(Mo) =95.94{+-}0.02 and with a much improved uncertainty interval. These 'absolute' isotope abundances also enable the Solar System abundances of molybdenum to be calculated for astrophysical purposes. Of particular interest are the Solar System abundances of the two p-process nuclides--{sup 92}Mo and {sup 94}Mo, which are present in far greater abundance than p-process theory suggests. The Solar System abundances for {sup 92}Mo and {sup 94}Mo of 0.364{+-}0.012 and 0.230{+-}0.008 respectively, (with respect to silicon =10{sup 6} atoms), are the most accurate values measured to date, and should therefore be adopted in future p-process calculations, rather than the existing values of 0.378{+-}0.021 and 0.236{+-}0.013, respectively.
- OSTI ID:
- 20995331
- Journal Information:
- Physical Review. C, Nuclear Physics, Vol. 75, Issue 5; Other Information: DOI: 10.1103/PhysRevC.75.055802; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2813
- Country of Publication:
- United States
- Language:
- English
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