Charge Radius of the Short-Lived Ni68 and Correlation with the Dipole Polarizability

Abstract

We present the first laser spectroscopic measurement of the neutron-rich nucleus 68 Ni at the N = 40 subshell closure and extract its nuclear charge radius. Since this is the only short-lived isotope for which the dipole polarizability αD has been measured, the combination of these observables provides a benchmark for nuclear structure theory. We compare them to novel coupled-cluster calculations based on different chiral two-and three-nucleon interactions, for which a strong correlation between the charge radius and dipole polarizability is observed, similar to the stable nucleus 48 Ca. Three-particle-three-hole correlations in coupled-cluster theory substantially improve the description of the experimental data, which allows to constrain the neutron radius and neutron skin of 68 Ni.

Nuclear Charge Radii of the Nickel Isotopes $^{58-68,70}$Ni

“…These values are in excellent agreement with independent measurements reported in [35]. Negligible deviations from our values in [18] arise from a correction in the analysis code but lead only to insignificant changes of δ r Theory. -Ab initio approaches compute the meansquare charge radius r 2 c starting from the calculated point-proton mean-square radius r 2 p ,…”

“…Results are listed in Table I. The changes in mean-square nuclear charge radii δ r 2 c 60,A ≡ r 2 c A − r 2 c 60 are obtained using the field-shift factor F = −783(94) MHz/fm 2 and the massshift factor M α=396 = 950(5) GHz u, as explained in [18]. These values are in excellent agreement with independent measurements reported in [35].…”

“…In this Letter, we report nuclear charge radii of nickel isotopes (Ni, Z = 28) which, in terms of R c , constitutes the last unexplored "magic" isotopic chain in this mass region. While the charge radius of 68 Ni was reported earlier [18], we here present additionally the results for 59,63,[65][66][67]70 Ni. The experimental data are compared with two DFT approaches as well as three independent ab initio methods based on chiral EFT interactions.…”

“…-The experiment at ISOLDE/CERN has been described previously in [18]. Details on the general setup can be found in [19].…”

A Guided Tour of ab initio Nuclear Many-Body Theory

“…Immediately after its inception, this approach was used to for the first ab initio calculations of dipole response and the related photodisassociation cross section of medium-mass closed-shell nuclei [241,242]. More recently, it was used to compute the electric dipole polarizability α D of nuclei like 48 Ca [243,244,246] and 68 Ni [247]. Together with measurements of the charge radius, this quantity can be used to constrain ab initio calculations that will in turn allow the theoretical extraction of the neutron point radius as well as the thickness of the neutron skin.…”