Isovector spin susceptibility: Isotopic evolution of collectivity in spin response

Abstract

Background: Response to spin-dependent operators has been investigated in the magnetic dipole and Gamow-Teller transitions, that provides magnetic properties of a nuclear system.Purpose: I investigate an isotopic dependence of the collectivity generated by the spin-dependent interactions in the Ca and Ni isotopes through the isovector (IV) spin-flip excitations. The responses in the neutral (tz) and charge-exchange (t±) channels are considered in a unified way.Method: A nuclear energy-density functional approach is employed for calculating the response functions based on the Skyrme-Kohn-Sham-Bogoliubov method and the quasiparticle-random-phase approximation (QRPA). I adopt the like-particle QRPA and the proton-neutron QRPA for the neutral and charge-exchange channels, respectively. I consider the fluctuation of the proton-neutron pair fields. Results:The collective shift due to RPA correlations for the response in the neutral channel is explained by the occupation probability of neutrons in the j> = +1/2 orbital. Many particle-hole or two-quasiparticle excitations have a coherent contribution to form a giant resonance in neutron-rich nuclei for the charge-exchange channel. The IV spin susceptibility displays the isotopic evolution of the collectivity and the underlying shell structure.Conclusions: A repulsive character of the residual interaction in the spin-isospin channel diminishes the IV spin susceptibility due to the collectivity, while the dynamic 3 S pairing appearing in the charge-exchange channel opposes the reduction.

Isovector giant monopole and quadrupole resonances in a Skyrme energy density functional approach with axial symmetry

“…Note that the pnQRPA calculations including the dynamic spin-triplet pairing with more or less the same strength as the spin-singlet pairing describe well the characteristic low-lying Gamow-Teller strength distributions in the light N Z nuclei [26][27][28], and the β-decay half-lives of neutron-rich Ni isotopes [29]. Furthermore, the present theoretical framework describes well the measured giant resonances in light, medium-heavy, and heavy nuclei [12,24,[30][31][32][33][34][35][36], and low-lying collective modes of vibration [12,[37][38][39][40][41].…”

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

“…The fluctuation of the S = 1 pair field and its effect on the observables has been discussed recently by investigating, e.g., the pn-pair transfer-type modes of excitation [14][15][16] and the spin susceptibility [17]. Furthermore, it has been known that the dynamical S = 1 pairing lowers the Gamow-Teller (GT) states in energy and thus shortens the β-decay half-lives of neutron-rich nuclei [18] including deformed nuclei [19].…”