Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28q.399m&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 399
Astronomy and Astrophysics
Astrophysics
Extinct Nuclides
Scientific paper
Type II supernovae are thought to be the result of the core collapse of massive stars. These catastrophic events disrupt much of the presupernova star, but often leave a roughly 1.4-solar-mass neutron star as a remnant. Several seconds after the collapse of the core, a high-entropy wind begins to blow from the surface of the nascent neutron star [1]. This wind is an ideal site for the r process of nucleosynthesis [2]. The nuclear abundance distribution produced in this wind agrees well with the solar-system r-process abundance distribution. In addition, the r-process yield in this wind is some 10^-4 solar masses, in good agreement with the amount expected from galactic chemical evolution arguments. One important implication is that the r process is not rare--most type II supernovae probably produce r-process nuclei. This contrasts with low-entropy supernova sites for the r process that typically produce 0.1 solar masses of r-process material per event and therefore must be rare [e.g., 3]. Several short-lived radioactive isotopes are produced in the r process. These are ^129I (half-life 15.7 m.y.), ^244Pu (half-life 80.8 m.y.), ^247Cm (half- life 15.6 m.y.), and ^107Pd (half-life 6.5 m.y.). Clear evidence exists for the presence of live ^129I [4], ^244Pu [5], and ^107Pd [6], while only an upper limit exists for ^247Cm [7]. Because of the short lifetimes of these nuclei, knowledge of their abundances in the early solar system and of their production in nucleosynthetic events yields important information about the chronology of the first few million years of the solar system's history and the last nucleosynthetic events contributing to the solar abundances. I have computed the production ratios of these short-lived radioactive isotopes in one particular model of the high-entropy r process. The results are ^107Pd/^110Pd = 0.66, ^129I/^127I = 2.03, ^244Pu/^238U = 0.36, and ^247Cm/^238U = 0.23. These ratios do not differ greatly from those already present in the literature, and the discrepancy between the free-decay timescales inferred from ^129I and ^244Pu (roughly 100 m.y.) and that from ^26Al (a few million years) remains. The production ratios presented above are for one particular r-process model. The ratios are sensitive to the details of the astrophysical model, for example, the velocity of the wind. Also, in the r process several components of differing degrees of neutron richness add together to give the final r- process abundances. It is not clear that the weighting of these different components is unique. The production ratios will be sensitive to the weighting of the components. The ratios are also sensitive to the properties of very- neutron-rich nuclei that are only known from theoretical nuclear-structure models [e.g., 8]. References: [1]} Duncan R. C. et al. (1986) Astrophys. J., 309, 141-160. [2] Meyer B. S. et al. (1992) Astrophys. J., 399, 656-664. [3] Hillebrandt W. et al. (1976) Astron. Astrophys., 52, 63-68. [4] Jeffery P. M. and Reynolds J. H. (1961) JGR, 66, 3582-3583. [5] Alexander E. C. et al. (1971) Science, 172, 837-840. [6] Kaiser T. and Wasserburg G. J. (1983) GCA, 47, 43-58. [7] Chen J. H. and Wasserburg G. J. (1981) EPSL, 52, 1-15. [8] Meyer B. S. et al. (1989) Phys. Rev. C., 39, 1876-1882.
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