Nuclear charge radius of $^8$He

TL;DR

This study measures the nuclear charge radius of the neutron-rich isotope ^8He for the first time, revealing a reduced size consistent with a neutron halo structure, using laser spectroscopy and atomic theory calculations.

Contribution

First measurement of the rms nuclear charge radius of ^8He, providing new insights into neutron correlations and halo structure in neutron-rich nuclei.

Findings

^8He charge radius = 1.93(3) fm

^6He charge radius = 2.068(11) fm

Reduction in charge radius indicates neutron halo formation

Abstract

The root-mean-square (rms) nuclear charge radius of ^8He, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of ^6He was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from ^6He to ^8He is an indication of the change in the correlations of the excess neutrons and is consistent with the ^8He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.