Measurement and microscopic description of odd–even staggering of charge radii of exotic copper isotopes

Abstract

Nuclear charge radii globally scale with atomic mass number A as A1∕3, and isotopes with an odd number of neutrons are usually slightly smaller in size than their even-neutron neighbours. This odd–even staggering, ubiquitous throughout the nuclear landscape1, varies with the number of protons and neutrons, and poses a substantial challenge for nuclear theory2–4. Here, we report measurements of the charge radii of short-lived copper isotopes up to the very exotic 78Cu (with proton number Z = 29 and neutron number N = 49), produced at only 20 ions s–1, using the collinear resonance ionization spectroscopy method at the Isotope Mass Separator On-Line Device facility (ISOLDE) at CERN. We observe an unexpected reduction in the odd–even staggering for isotopes approaching the N = 50 shell gap. To describe the data, we applied models based on nuclear density functional theory5,6 and A-body valence-space in-medium similarity renormalization group theory7,8. Through these comparisons, we demonstrate a relation between the global behaviour of charge radii and the saturation density of nuclear matter, and show that the local charge radii variations, which reflect the many-body polarization effects, naturally emerge from A-body calculations fitted to properties of A ≤ 4 nuclei.

Evidence of a sudden increase in the nuclear size of proton-rich silver-96

“…In order to investigate these qualitative observations in more detail, DFT calculations, using Fayans (Fy) 40 and UNEDF 41 , 42 Skyrme Energy Density Functionals (EDF), were performed. Recently, the effectiveness of the Fy(Δ r , HFB) 43 parameterization on reproducing total radii 14 , 35 , 36 , 44 as well as smaller odd-even variations, such as the odd-even staggering in copper 13 isotopes, was demonstrated. The (Δ r ) parametrization has furthermore demonstrated the ability to reproduce the changes of nuclear charge radii when crossing shell closures for both proton-rich calcium ( Z = 20) isotopes 44 as well as neutron-rich Sn ( Z = 50) 36 isotopes.…”

“…Measurements of atomic hyperfine structure and isotope shifts provide nuclear-model independent access to the nuclear spin, magnetic dipole, and electric quadrupole moments as well as changes in root-mean-square charge radii 11 . The nuclear charge radius provides insight into the shell and subshell effects 12 , correlations and mixing 13 , and nuclear deformation 14 . The recent demonstration of the charge radii’s sensitivity to aspects of nuclear structure 15 has allowed testing of ab initio methods, density functional approaches, and SM calculations 16 .…”

Laser spectroscopy of indium Rydberg atom bunches by electric field ionization

“…The use of ion cooling and bunching has allowed highly sensitive measurements of exotic atoms and molecules containing short-lived isotopes to date 1 , 3 , by concentrating measurements on ion bunches into a narrow time window, in order to improve background suppression and additionally allowing a high duty cycle for high-resolution and high-detection efficiency pulsed laser ionization spectroscopy 20 , 42 , 43 .…”

“…Furthermore, sensitive detection or separation of small quantities of isotopes also has numerous technological applications 5 – 11 . Fast beam collinear laser spectroscopy techniques have allowed high-precision measurements on short-lived isotopes, down to rates of fewer than 100 ions per second 3 , 12 , 13 . These approaches use the Doppler compression of an accelerated atomic beam to enable high-precision laser spectroscopy measurements to be performed in a collinear geometry 14 , 15 .…”

E1moments from a coherent set of measured photoneutron cross sections

“…Finally, note that the integrated photoabsorption cross section and the centroid energy can be related to the charge mean square radius and the mean proton distance [60,61] and similarly the polarizability is directly proportional to the mean square radius [12]. Since mean-field models with blocking techniques are known to reproduce rather well charge radii, including the odd-even staggering [62,63], we can expect our blocking approximation in the Gogny-HFB mass model to give a fair, though not complete, representation of the E 1 moments in odd-even nuclei.…”