Researchers from the University of Jyväskylä in Finland have made a groundbreaking discovery about the ‘magic’ N=50 neutron shell closure, providing detailed data that could revolutionize our understanding of nuclear forces and the atomic nucleus.
Puzzling Out the N=50 Shell
The region below the double magic nucleus 100Sn has been targeted by the research team due to its plethora of nuclear structure phenomena.
Their most recent work has shed new light on the impact of the neutron number N=50 magic shell closure in silver isotopes. They are, however, important because the nuclear properties of this region (e.g., binding energies) play a crucial role in shell closure stability and evolution of single-particle energies.
Employing the advanced phase-imaging ion-cyclotron resonance (PI-ICR) technique combined with a laser spectroscopic hot-cavity catcher ion source, researchers investigated the magic N = 50 neutron shell closure in exotic silver isotopes with unmatched precision. This made it possible for them to measure ground-state masses of silver-95, -96, and -97 nuclei plus an isomeric state in silver-96 with a precision of around 1 keV/c² even for very low yield.
Results – Benchmarking Nuclear Models and Astrophysical Processes
Mass values measured in this study of silver isotopes for masses around N = 50 quantify the stability of the N = 50 shell closure, which provides key input to refine nuclear forces and confront theoretical models.
The excitation energy of the silver-96 isomer defines a benchmark case for ab initio predictions of observables not determined by the ground state, indispensable in appraising theoretical approaches to odd-odd constituents near tin-100 along with accreting such nuclei in r0A competitions.
Even more significantly, the new accurate measurement of the silver-96 isomer excitation energy makes it possible to decouple the ground state and isomer in astrophysical models, thus providing a better description of processes such as rapid proton capture.
The researchers stress all of the theoretical approaches employed, in particular ab initio, density functional theory, and shell model calculations, are challenged when it comes to capturing the trend of nuclear ground-state properties as one moves across the N = 50 neutron shell and towards the proton dripline. One is that their measurements provide vital information on which to improve these models and hence our global understanding of the atomic nucleus.
Conclusion
The University of Jyväskylä research team’s new work is a quantum leap forward in uncovering the ‘magic’ N=50 neutron shell closure and the nuclear strong force, which underpins so much of what we currently know about the nucleus. Combined with innovative experimental strategies and high-precession mass measurements, these experiments have both confirmed our theoretical models and developed new capabilities for the future of nuclear physics. They call the new research a major step in an ongoing quest to understand how atomic nuclei form and behave, knowledge that informs fields from astrophysics to nuclear energy.
