Nuclear magic numbers: New features far from stability

Atomic physics techniques for the determination of ground-state properties of radioactive isotopes are very sensitive and provide accurate masses, binding energies, Q-values, charge radii, spins and electromagnetic moments. Many fields in nuclear physics benefit from these highly accurate numbers. They give insight into details of the nuclear structure for a better understanding of the underlying effective interactions, provide important input for studies of fundamental symmetries in physics, and help to understand the nucleosynthesis processes that are responsible for the observed chemical abundances in the Universe. Penning-trap and storage-ring mass spectrometry as well as laser spectroscopy of radioactive nuclei have now been used for a long time but significant progress has been achieved in these fields within the last decade. The basic principles of laser spectroscopic investigations, Penning-trap and storage-ring mass measurements of short-lived nuclei are summarized and selected physics results are discussed.

https://iopscience.iop.org/article/10.1088/0031-8949/2013/T152/014017/pdf

Precision Atomic Physics Techniques for Nuclear Physics with Radioactive Beams

The nuclear structure in regions of the Segre chart which are of astrophysical importance is reviewed. The main emphasis is put on those nuclei that are relevant for stellar nucleosynthesis in fusion processes, and in slow neutron capture, both located close to stability, rapid neutron capture close to the neutron dripline and rapid proton capture near the proton dripline. The basic features of modern nuclear structure, their importance and future potential for astrophysics and their level of predictibility are critically discussed. Recent experimental and theoretical results for shell evolution far off the stability line and consequences for weak interaction processes, proton and neutron capture are reviewed.

https://iopscience.iop.org/article/10.1088/0034-4885/70/9/R02/pdf

Nuclear structure and astrophysics

We have performed large-scale shell-model calculations of the half-lives and neutron-branching probabilities of the $r$-process waiting-point nuclei at the magic neutron numbers $N=50$, 82, and 126. The calculations include contributions from allowed Gamow-Teller and first-forbidden transitions. We find good agreement with the measured half-lives for the $N=50$ nuclei with charge numbers $Z=28$--32 and for the $N=82$ nuclei ${}^{129}$Ag and ${}^{130}$Cd. The contribution of forbidden transitions reduce the half-lives of the $N=126$ waiting-point nuclei significantly, while they have only a small effect on the half-lives of the $N=50$ and 82 $r$-process nuclei.

Shell-model half-lives including first-forbidden contributions for r -process waiting-point nuclei

Current status of r -process nucleosynthesis

The gamma decay of excited states in the waiting-point nucleus Cd-130(82) has been observed for the first time. An 8(+) two-quasiparticle isomer has been populated both in the fragmentation of a Xe-136 beam as well as in projectile fission of U-238, making Cd-130 the most neutron-rich N=82 isotone for which information about excited states is available. The results, interpreted using state-of-the-art nuclear shell-model calculations, show no evidence of an N=82 shell quenching at Z=48. They allow us to follow nuclear isomerism throughout a full major neutron shell from Cd-98(50) to Cd-130(82) and reveal, in comparison with Ni-76(48) one major proton shell below, an apparently abnormal scaling of nuclear two-body interactions.

K. Langanke

Papers

Observation of Isomeric Decays in the r-Process Waiting-Point Nucleus 130 Cd 82