Session 4WEA: Perspectives for Decay Spectroscopy with Fast Fragmentation Beams I

Large-scale shell-model study for beta-decay properties of neutron-rich nuclei

Beta decays in neutron-rich nuclei provide beneficial information on nuclear structure through their selective populations of states with specific spin/parity quantum numbers. Among them, the halflives of neutron-rich nuclei are important to elucidate r-process nucleosynthesis. In this talk, we present our shell-model study about the beta-decay properties of neutron-rich N=82, 81 isotones, some of which are r-process waiting point nuclides. The shell-model result shows excellent agreement with the experimental half-lives. We found that the low-energy peak of the Gamow Teller transition increases as the proton number

decreases from Z=50 to Z=40 due to the shell evolution. In addition, the beta-decay half-lives of neutron-rich nuclei of A~40 nuclei

are estimated by the shell-model calculations including the recently measured data at the FRIB facility.   

Beta-decay properties and r-process observables

A primary goal of our current era of multimessenger astrophysics is to untangle the origins of the heaviest elements via rapid neutron capture (r-process) nucleosynthesis. FRIB offers an exciting opportunity to dramatically reduce the nuclear data uncertainties that plague the r-process simulations used to constrain r-process sites of production. Here we focus on the key role played by beta-decay properties on shaping r-process observables and describe future prospects for r-process studies enabled by the FRIB Decay Station.    

Experiments related to r-process nucleosynthesis

Where and how were heavy elements which contain many neutrons relative to proton, synthesized? With regards to the origin of these heavy elements, a reaction in which nuclei capture neutrons in a fast and continuous manner during the explosion of a star was proposed and named the rapid neutron capture process (r process) [1].

In 2017, a binary neutron star merger event was discovered by simultaneous observations of gravitational and electromagnetic waves, and its kilonova was also identified, suggesting the synthesis of heavy elements. Were heavy elements such as gold, platinum, and even uranium synthesized in binary neutron star mergers, supernova explosions, or collapsars [2-4]? Analysis of the unique heavy-element compositions left behind in the solar system, meteorites, and old metal-poor stars has begun. The key to deciphering the traces left behind by isotopic elements lies in the thousands of neutron-rich nuclei that disappeared in an instant.

Here, we introduce the experimental research on the explosive r-process nucleosynthesis and future perspective at RIBF [5,6].

 

[1] E.M. Burbidge, G.R. Burbidge, W.A. Fowler, and F. Hoyle, Rev. Mod. Phys. 29, 547 (1957).

[2] S. Wanajo et al., Astrophys. Jour. Lett. 789: L39 (2014).

[3] C. Kobayashi, A.I. Karakas, and M. Lugaro, Astrophys. Jour. 900, 179 (2020).

[4] J. Barnes and B.D. Metzger, Astrophys. Jour. Lett. 939: L29 (2022).

[5] V.H. Phong et al., Phys. Rev. Lett. 129, 172701 (2022).

[6] S. Nishimura, Prog. Theor. Exp. Phys. 2012, 03C006 (2012).