Evidence for 40Ca core excitation from g factor and B(E2) measurements on the 21+ states of 42,44Ca

Ground-state electromagnetic moments of calcium isotopes

“…These calculations include up to 6p-6h for 41 Ca, 4p-4p for 43 Ca, and 2p-2p for the other isotopes. A similar conclusion on the importance of cross-shell correlation across N = 20 was obtained from experimental g(2 + ) factors and B(E2) values of 42,44 Ca [47,48] as well as the calcium isotope shifts [49]. For the heavier Ca isotopes, all theoretical calculations describe the experimental value rather well (see Fig.…”

“…In this Rapid Communication, we report the first measurements of the quadrupole moment of the closed shell −1 isotope 47 Ca, and the quadrupole and magnetic moment of the closed-shell +1 isotope 49 Ca. 1 Also the magnetic and quadrupole moments of 51 Ca, having a single-hole with respect to the new N = 32 subshell closure, are presented, as well as its ground state (g.s.)…”

“…Methods: High-resolution bunched-beam collinear laser spectroscopy was used to measure the optical hyperfine spectra of the 43−51 Ca isotopes. Results: The ground-state magnetic moments of 49,51 Ca and quadrupole moments of 47,49,51 Ca were measured for the first time, and the 51 Ca ground-state spin I = 3/2 was determined in a model-independent way. Our experimental results are compared with state-of-the-art shell-model calculations using both phenomenological interactions and microscopic interactions derived from chiral effective field theory.…”

Magnetic dipole probes of the sd and pf shell crossing in the 36,38Ar isotopes

“…In particular, the data show already some M1 strength around 8 MeV, which is missing in the calculation. This is possibly improved if npnh configurations with n > 4 were included -previous shell model studies [7,8,13,14] indicated that energies of the states in nuclei around 40 Ca are converging rather slowly when npnh cross-shell excitations with larger n are gradually added. While such converged calculations are yet impossible in the complete sdpf shell, they are, however, feasible in the sdpf 0 and sdpf 1 model spaces (see text above) to which we turn in the next section.…”

“…For this nucleus, these include the observation of a strong M1 transition [2] and of a non-vanishing Gamow-Teller (GT) strength built on the 40 Ca ground state [4,5,6]. On the theory side, recent studies [7,8] show that there are very large admixtures of sd configurations in low-energy states of Ca isotopes with A ≥ 40, although these nuclei are usually considered as "good" pf shell nuclei. Another indication for the erosion of the sd-pf closure near A = 40 are the data for the M1 strength in 36 Ar and 38 Ar [9].…”