Charge Exchange Spin-Dipole Excitations of 90Zr and the Neutron Skin Thickness

Charge exchange spin-dipole (SD) excitations of 90Zr are studied by the 90Zr(p, n) and 90Zr(n, p) reactions at 300 MeV. A multipole decomposition technique is employed to obtain the SD strength distributions in the cross section spectra. A model-independent SD sum rule value is obtained: 148±12 fm2. The SD strength distributions and the sum rule value are compared with the calculated results of the self-consistent Skyrme Hartree-Fock + Tamm-Dancoff approximation with the coupling to the continuum. The neutron skin thickness of 90Zr is determined to be 0.07±0.04 fm from the SD sum rule.