A proton density bubble in the doubly magic $^{34}$Si nucleus

TL;DR

This paper provides experimental evidence for a proton density bubble in the short-lived nucleus 34Si, revealing a central depletion that informs nuclear structure models and the spin-orbit interaction.

Contribution

First experimental observation of a proton density bubble in 34Si, offering new insights into nuclear density distributions and the spin--orbit force.

Findings

Evidence of proton density depletion in 34Si

Implications for nuclear model constraints

Insights into spin--orbit interaction dependence

Abstract

Many properties of the atomic nucleus, such as vibrations, rotations and incompressibility, can be interpreted as due to a two component quantum liquid of protons and neutrons. Electron scattering measurements on stable nuclei demonstrate that their central densities are saturated, as for liquid drops. In exotic nuclei near the limits of mass and charge, with large imbalances in their proton and neutron numbers, the possibility of a depleted central density, or a 'bubble' structure, has been discussed in a recurrent manner since the 1970s. Here we report first experimental evidence that points to a depletion of the central density of protons in the short-lived nucleus 34Si. The proton-to-neutron density asymmetry in 34Si offers the possibility to place constraints on the density and isospin dependence of the spin--orbit force-on which nuclear models have disagreed for decades-and on its stabilizing effect towards limits of nuclear existence.