Quenching of single particle spin-isospin operators with δℓ=1 and higher multipoles in medium heavy nuclei

Abstract

Spin-isospin mode β-and γ- transitions with Δℓ =1 between low-lying single particle states in medium heavy nuclei are shown to be quenched uniformly by factors 34̃ in comparison with shell model calculations without coherent effects of spin-isospin polarizations. The quenching factors are analyzed, in terms of the nucleon mode NN −1 spin isospin polarization and the higher excitation XN −1 mode spin-isospin polarization. The RPA is used for the separable particle-hole polarization interaction. The observed values of the quenching factor g eff/g for the single particle spin-isospin transition and of the excitation energy E GR for the relevant spin-isospin giant resonance are represented n terms of the NN −1 polarization strength and the XN −1 mode one. The nucleon NN −1 polarization strength f τ ≈ 1.15 reproduces both the IAS-Elγ quenching factors and the Elγ giant resonance energies, while the spin isospin mode requires a finite contribution of the higher mode strength of h τσ ≈0.4 in addition to the MN mode strength of f τσ ≈1.35 to explain both the quenching factor of the single particle transition rate and. the τσY 1, giant resonance energy observed in (p, n) reactions. The strong spin isospin mode at high excitation region is discussed in terms of the isobar (Δ) N −1 effect and the tensor interaction effect.