Unexpectedly large charge radii of neutron-rich calcium isotopes

Abstract

Despite being a complex many-body system, the atomic nucleus exhibits simple structures for certain ‘magic’ numbers of protons and neutrons. The calcium chain in particular is both unique and puzzling: evidence of doubly magic features are known in ^40,48Ca, and recently suggested in two radioactive isotopes, ^52,54Ca. Although many properties of experimentally known calcium isotopes have been successfully described by nuclear theory, it is still a challenge to predict the evolution of their charge radii. Here we present the first measurements of the charge radii of ^49,51,52Ca, obtained from laser spectroscopy experiments at ISOLDE, CERN. The experimental results are complemented by state-of-the-art theoretical calculations. The large and unexpected increase of the size of the neutron-rich calcium isotopes beyond N = 28 challenges the doubly magic nature of 52Ca and opens new intriguing questions on the evolution of nuclear sizes away from stability, which are of importance for our understanding of neutron-rich atomic nuclei

In-medium similarity renormalization group for closed and open-shell nuclei

“…The drops in the theoretical S 2n in 48,52,54 Ca, corresponding to the hypothetical shell closures N = 28, 32, 34, suggests that these nuclei are magic for the used interaction, matching predictions from Shell model calculations with interactions derived from chiral N N +3N forces in MBPT [178,179]. While this view was supported by precision mass measurements [176,180,181], a recent experiment found an unexpectedly large charge radius of 52 Ca, which puts the magicity of the neutron number N = 32 in question [141] (also see [182]). The flat trend of the calcium ground-state energies is reflected by the small values of the separation energies in isotopes beyond 54 Ca.…”

“…In section 6, we will present MR-IMSRG results with one of the first new N N +3N interactions that resulted from these efforts, NNLO sat [26]. By taking select many-body data into account in the optimization procedure, the creators of NNLO sat were able to improve the interaction's saturation properties, allowing an accurate description of the ground-state energies and radii of 40,48 Ca [140,141].…”

High-precision QEC -value measurement of the superallowed β+ emitter Mg22 and an ab

“…The second NN+3N interaction, 1.8/2.0(EM) [49][50][51], uses the same initial NN interaction as above but is SRG-evolved to λ NN = 1.8fm −1 , with undetermined 3N force couplings fit to reproduce both the triton binding and alpha particle charge radius at λ 3N = 2.0fm −1 . This Hamiltonian reproduces groundstate energies across the nuclear chart from the p shell to the tin region [51][52][53][54]. The resulting calculations of the IAS states are compared to the experimental data from this work and Ref.…”

Doubly magic nuclei from lattice QCD forces at MPS=469MeV/c2

“…Their use with soft interactions from chiral effective field theory have led to first-principle predictions of experimental total binding energies [31,32] and nuclear radii [33][34][35] with unprecedented accuracies. Interactions like the HAL QCD potentials pose a bigger challenge for calculations of medium mass isotopes due to their short-distance internucleon repulsion.…”