A short comment on long half-lives
DOI: 10.1063/1.3528995
It surprised me to see calcium-48 classed with nickel-56 as a doubly magic nuclide with a long half-life, as was stated in Physics Today (August 2010, page 16 ). The half-life of 56 Ni is only 6 days, while that of 48Ca is given by the Brookhaven National Laboratory webpage http://www.nndc.bnl.gov/chart as 2 × 1019 years.
Calcium-48 has been considered stable, at least until the mid 1990s. The nuclide is so neutron rich that even the small amount present in cosmic materials is a problem for schemes of nucleosynthesis. 1 Nevertheless, Fiorella Castelli and Swetlana Hubrig were able to identify the nuclide in the spectra of chemically peculiar stars 2 because of the large isotope shift of lines of the Ca II infrared triplet. Varying isotopic ratios of 48Ca may be found in chemically peculiar stars, and in a few cases, the isotope shifts are compatible with the Ca being pure or very nearly pure 48Ca. 3
References
1. D. Clayton, Handbook of Isotopes in the Cosmos: Hydrogen to Gallium, Cambridge U. Press, New York (2003).
2. F. Castelli, S. Hubrig, Astron. Astrophys. 421, L1 (2004).
3. C. R. Cowley, S. Hubrig, J. F. González, Mon. Not. R. Astron. Soc. 396, 485 (2009).
More about the Authors
Charles R. Cowley. (cowley@umich.edu) University of Michigan Ann Arbor, US .
