Spin–isospin properties of $$\varvec{N=Z}$$ odd–odd nuclei from a core+$$\varvec{pn}$$ three-body model including core excitations

Abstract

Background: For N = Z odd-odd nuclei, a three-body model assuming two valence particles and an inert core can provide an understanding of pairing correlations in the ground state and spin-isospin excitations. However, since residual core-nucleon interactions can have a significant impact on these quantities, the inclusion of core excitations in the model is essential for useful calculation to be performed. Purpose: The effect of core excitations must be included in order to gain a detailed understanding of both the ground state and spin-isospin properties of these systems. To this end, we include the vibrational excitation of the core nucleus in our model. Methods: We solve the three-body core-nucleon-nucleon problem including core vibrational states to obtain the nuclear ground state as well as spin-isospin excitations. The core vibrational states are described by the randomphase-approximation. The spin-isospin excitations are examined from the point of view of SU(4) multiplets. Results: By including the effect of core excitation, the following experimental quantities of N = Z odd-odd nuclei are better described: (a) the magnetic moment of the ground states, (b) the energy difference between the first 0 + and 1 + states, and (c) the B(M 1) and B(GT) between 0 + and 1 + states. In addition, the coupling with the core vibration induces quenching and damping in B(M 1) and B(GT), and the root mean square distances between proton and neutron and that between the center of mass of proton and neutron and core nucleus increase. Large B(M 1) and B(GT) observed for 18 F and 40 Ca were explained in terms of the SU(4) symmetry. Conclusions: The core nucleus is meaningfully broken by the residual core-nucleon interactions, and various quantities concerning spin-isospin excitations as well as the ground state become consistent with experimental data. Including the core excitation in the three-body model is thus important for a more detailed understanding of nuclear structure.

Symmetry breaking of Gamow-Teller and magnetic-dipole transitions and its restoration in calcium isotopes

“…The GT and M1 transitions can be approximately understood on an equal footing in the context of the isobaric analog states [9,[41][42][43][44][45]. However, it is well known that both types of excitation are remarkably affected by so-called residual interactions [17,35,36,38,39,46].…”

“…However, it is well known that both types of excitation are remarkably affected by so-called residual interactions [17,35,36,38,39,46]. In open-shell nuclei, the effect of isoscalar and isovector pairing correlations has been shown as relevant [40,45,47,48]. The isobaric-analog symmetry between the GT and M1 transition properties in real systems has not been completely clarified.…”

Spin-triplet proton-neutron pair in spin-dipole excitations

“…The effects of the S = 1 pair interaction on the GT transition strengths have been thoroughly studied * E-mail: kyoshida@ruby.scphys.kyoto-u.ac.jp in N = Z odd-odd nuclei with a three-body model of two nucleons around a spherical core [21][22][23]. A remarkable feature found in N = Z odd-odd nuclei with an LS-closed core ( 4 He, 16 O, 40 Ca) is the appearance of the low-energy state with a strong GT strength.…”

Spin-triplet proton-neutron pair in spin-dipole excitations

“…The effects of the S = 1 pair interaction on the GT transition strengths have been thoroughly studied in N = Z odd-odd nuclei with a three-body model of two nucleons around a spherical core [28][29][30]. A remarkable feature found in N = Z odd-odd nuclei with an LS-closed core ( 4 He, 16 O, 40 Ca) is the appearance of the low-energy state with a strong GT strength.…”