Separation of pygmy dipole and M1 resonances in 90Zr by a high-resolution inelastic proton scattering near 0°.

ABSTRACT

A high-resolution measurement of inelastic proton scattering off (90)Zr near 0° was performed at 295 MeV with a focus on a pronounced strength previously reported in the low-energy tail of giant dipole resonance. A forest of fine structure was observed in the excitation energy region 7-12 MeV. A multipole decomposition analysis of the angular distribution for the forest was carried out using the ECIS95 distorted-wave Born approximation code with the Hartree-Fock plus random-phase approximation model of E1 and M1 transition densities and inclusion of E1 Coulomb excitation. The analysis separated pygmy dipole and M1 resonances in the forest at E(PDR)=9.15±0.18 MeV with Γ(PDR)=2.91±0.64 MeV and at E(M1)=9.53±0.06 MeV with Γ(M1)=2.70±0.17 MeV in the Lorentzian function, respectively. The B(E1)↑ value for pygmy dipole resonance over 7-11 MeV is 0.75±0.08 e(2)fm(2), which corresponds to 2.1±0.2% of the Thomas-Reiche-Kuhn sum rule.