Speaker
Description
The third r-process yield peak at mass A ∼190 is the consequence of the N=126 neutron shell closure. Yield calculations need information on both astrophysical environment and nuclear properties. The N=126 isotones directly involved in the r process are much more neutron-rich than those that can currently be populated in laboratories, consequently theories predicting their properties have to be tested on available experimental information on nuclei closer to stability.
It is often claimed that the study of nuclei close to stability can be used to improve models/parametrisations, and therefore, increase their predicting power for more exotic nuclei. Here we aim to address this claim for the case of neutron-rich N=126 isotones, employing the shell model. The simple idea is that the measurable excited-state energies as well as transition strength values, reflect the behaviour of the different proton orbitals and their interactions. For example, the 11/2− state, dominated by the πh11/2 orbital, is expected to be the ground-state of N=126 nuclei on the r-process path; this same high-j orbital is responsible for the isomeric states in nuclei which can already be synthesised in the laboratory.
Shell model calculations for the neutron-rich N=126 206Hg – 198Lu (Z=80–71) isotones were performed with two different parametrisations. The one refined to explain the isomerism in 204Pt [1] was found to be the only one able to reproduce the more recent data on 203Ir [2] , and in general, to give a better reproduction of the nuclei in this region. For more exotic nuclei approaching the r-process path, this refined parametrisation predicts the existence of isomeric states with spin-parities 5− and 10+ in the even-mass and 19/2 + in the odd-mass isotones. Also, they predict ground-state spin-parities of 3/2 + for 201Re and 11/2− for 199Ta and 197Lu, with low-energy long-lived isomers present. The remaining deficiencies are related to the properties of the πd5/2 orbital and are influenced by octupole collectivity. The presented predictions [3] provide guidance and can be tested in the near future at radioactive-beam facilities.
[1] S.J. Steer et al., Phys. Rev. C78, 061302(R) (2008).
[2] G. Bartram et al., submitted to Phys. Lett. B.
[3] Zs. Podolyak, C.J. Wilson, submitted.