Shell Evolutions and Nuclear Forces

O Sorlin

doi:10.1051/epjconf/20146601016

Abstract

During the last 30 years, and more specifically during the last 10 years, many experiments have been carried out worldwide using different techniques to study the shell evolution of nuclei far from stability. What seemed not conceivable some decades ago became rather common: all known magic numbers that are present in the valley of stability disappear far from stability and are replaced by new ones at the drip line. By gathering selected experimental results, beautifully consistent pictures emerge, that very likely take root in the properties of the nuclear forces.The present manuscript describes some of these discoveries and proposes an intuitive understanding of these shell evolutions derived from observations. Extrapolations to yet unstudied regions, as where the explosive r-process nucleosynthesis occurs, are proposed. Some remaining challenges and puzzling questions are also addressed.

Highlights

When sorting out the data available to date, amazingly similar pictures arise throughout the chart of nuclides, which have been recently identified to take root from specific properties of the nuclear force and from nuclear correlations
It was proposed here that the reduction of the N=8, 20, and 40 shell gaps and the swapping between certain levels arise from a simple hierarchy between proton-neutron forces
This hierarchy was applied to yet unexplored regions of the chart of nuclides such as below 42Si, 64Cr, 78Ni or below 132Sn where the r-process nucleosynthesis is accumulating peaks in the r abundance curve of the elements

Summary

Introduction

To give an example, using yet available experimental data, the N=14, 28 and 50 SO shell gaps increase by the same value of about 2.7 MeV when the neutron orbits d5/2, f7/2 and g9/2 are filled, respectively [5] This points to a universal mechanism that cannot be accounted for by one-body potentials for which a single parametrization cannot lead to such modifications in a given isotopic chain. In which the ordering of the intruder and normal configurations is inverted belong to the so-called "Island of Inversion" [15] These pioneering discoveries in the N=20 region opened a new branch of experimental and theoretical researches related to the structure of nuclei far from stability. A generalization of this mechanism to other regions of the chart of nuclides (around 60Ca, below 78Ni and below 132Sn where the r-process nucleosynthesis occurs) will be proposed

Remarkable properties of the HO magic numbers

The Island of Inversion

2.72 MeV that

Hierarchy of nuclear forces: toward a universal mechanism?

Nuclear forces at the drip line

Summary and Perspectives