Some Nucleosynthesis Effects Associated withr‐Process Jets

Abstract

In a recent work, I have discussed some of the consequences of including rotation and magnetic fields in a model of a core-collapse supernova. Rotation produces equatorial flattening in the resultant neutron star and also produces a surrounding accretion disk. Magnetic fields wrap into a toroid that extrudes material in the equatorial plane. The combination of these effects is an accretion-extrusion disk that feeds material into bipolar jets rooted in the disk where the inward and outward flows meet. The extrusion flow is the site of an r-process in which the seed nuclei embedded in the neutron Fermi sea in the outer neutron star envelope capture the neutrons in which they are embedded. At high latitudes on the neutron star a large neutrino-antineutrino flux drives a neutron wind of the type previously discussed for spherical models, and this is a separate site for a less efficient r-process. In the high-temperature accretion disk, nuclear statistical equilibrium exists, with an abundance peak near mass number 90. The jets are expected to have a velocity of about 0.5c (140 MeV nucleon-1) and to blast holes in the expanding envelope of the supernova, causing large secondary explosions and extensive spallation of both the envelope and jet nuclei. The general purpose of this paper is to discuss nuclear processes and effects associated with this rather complicated scenario and to identify features in the nuclidic abundances in solar system materials that are probably associated with these effects. One discussion tentatively identifies the fission point for r-process fission recycling with the nuclide 297Bh and argues for fission peaks around mass numbers 132 and 165, identifying the latter with an r-process abundance hump in the rare earth region. The equilibrium abundance peak at mass number 90 should be involved in creating the abundance peak in the p-process in that region, previously not understood. Spallation of r-process nuclei near the mass number 132 peak can be identified with an unusual Xe component in interstellar nanodiamonds called Xe-HL. A discussion is given of other isotopic anomalies in meteoritic components that imply mixing and turbulence in the expanding supernova envelope, and it identifies the macroscopic calcium-aluminum inclusions in meteorites as originating in the envelope of a supernova responsible for triggering formation of the primitive solar nebula. Spallation can also be expected to produce DLiBeB fragments in the CO and He layers of the envelope as a primary process, in contrast to cosmic-ray production of such fragments in secondary processes.