Session K05: R-Process and Shell Evolution Near Doubly-Magic 78Ni

Laser Spectroscopy as a Probe of Nuclear Structure in the Vicinity of $^{\mathrm{78}}$Ni

Of the many observables that are available to probe the nucleus, the nuclear electromagnetic moments and the charge radius have proven particularly sensitive probes of nuclear structure effects. These observables can readily be extracted from measurements of the atomic hyperfine structure using laser spectroscopic methods. The study of exotic (very short-lived) radioactive isotopes requires ultra-sensitive laser spectroscopy techniques, which are under continuous development at radioactive beam facilities. A particular region of interest for nuclear structure studies is the region around the exotic isotope $^{\mathrm{78}}$Ni, an isotope that is predicted to have a doubly-magic character. At the ISOLDE facility in CERN, many laser spectroscopy experiments have been working towards the doubly magic $^{\mathrm{78}}$Ni, and the isotopes in its vicinity. In this contribution, an overview of recent results obtained on neutron-rich Gallium, Zinc, Copper and Nickel will be given. Emphasis will be placed on the most recently obtained radii and electromagnetic moments of neutron-rich Copper ($^{\mathrm{76-78}}$Cu), Zinc (up to $^{\mathrm{79}}$Zn), and Nickel (up to $^{\mathrm{70}}$Ni). Where possible, the complementarity of these results and other observables will be highlighted. These results were obtained with two complimentary high-resolution laser spectroscopy techniques, namely collinear laser spectroscopy and collinear resonance ionization spectroscopy (CRIS). The principle of these methods will be briefly introduced, emphasizing specifically how the strengths of the two methods enable the measurements on exotic isotopes.   

Decay Spectroscopy in the Region of $^{78}Ni$

The simultaneous development of advanced astrophysical models [1] and new facilities capable of producing rapid neutron capture (r-process) nuclei with sufficient yields to measure their masses and decay half-lives [2] has spurred a renaissance of the field. Now-available realistic r-process calculations in neutron binary mergers [3] show that the properties of nuclei in the vicinity of doubly magic $^{78}$Ni, $^{132}$Sn and $^{208}$Pb are the largest contributors to the final abundance pattern [4]. These nuclei are simultaneously the hardest to model using global nuclear models [5] and to produce in nuclear physics facilities [2].\\ \\ Detailed decay-spectroscopy measurements of r-process nuclei close to magic numbers can offer a wealth of nuclear structure information to improve nuclear models. However, large neutron branching ratios have traditionally impeded complete observations. The Versatile Array for Neutron Detectors (VANDLE) was developed at UTK for neutron spectroscopy using the time-of-flight technique. Here we will discuss the delayed neutron emission from neutron rich $^{83,84}$Ga isotopes measured with VANDLE and a new microscopic model of their decay capable to reproduce their decay properties.\\ \\ {[1]} A. Arcones and G. Martínez-Pinedo, Phys. Rev. C 83, 045809 (2011).\\ {[2]} S. Nishimura et al., Phys. Rev. Lett. 106, 052502 (2011).\\ {[3]} B. P. Abbott et al. Phys. Rev. Lett. 119, 141101 (2017).\\ {[4]} M. Mumpower et al., Prog. Part. Nucl. Phys. 86, 86 (2016).\\ {[5]} P. M\"oller, B. Pfeiffer, and K.-L. Kratz, Phys. Rev. C 67, 055802 (2003).   

Nuclear Structure from First Principles in the ${}^{78}$Ni Region

In recent years, the ${}^{78}$Ni region has become accessible with advanced many-body methods like Coupled Cluster or the In-Medium Similarity Renormalization Group. I will present a brief overview of the state of the art of these approaches, with an emphasis on the precision that can be achieved for energies and other observables. I will survey results for ground- and excited-state properties of nuclei around ${}^{78}$Ni, and discuss how new experimental data can help us refine the next generation of chiral nuclear interactions and observables that are the dominant source of theoretical uncertainty in modern nuclear many-body calculations.