Proton scattering at intermediate energies on ${}^{58}\mathrm{Ni}$: How well is it understood?

The excitation-energy region up to 23 MeV in ${}^{58}\mathrm{Ni}$ has been investigated with the ($\overrightarrow{p},{\overrightarrow{p}}^{\text{'}})$ reaction at an incident energy of 172 MeV and forward angles favoring the excitation of the spin-dipole mode in the continuum. The measured cross sections, spin-flip cross sections, and spin-flip probabilities are compared to microscopic reaction-model calculations using various effective projectile-target interactions. The nuclear structure input, which takes into account one-particle one-hole (1p1h) as well as two-particle-two hole (2p2h) excitations, allows for a reasonable description of the continuum region well above the particle-decay thresholds. However, considerable problems remain in the description of spin-flip resonances at lower excitation energies, which cannot be explained by a quenching of the spin-isospin interaction.

Figure 1

Experimental cross sections for the ${}^{58}\mathrm{Ni}$($\overrightarrow{p},{\overrightarrow{p}}^{\text{'}})$ reaction at $E_0=172$ MeV and theoretical predictions using QPM wave functions and models I (dotted lines), II (dashed lines), and III (solid lines) for the effective target-nucleon interaction explained in the text.

Figure 2

Spin-flip cross sections of the ${}^{58}\mathrm{Ni}$$(\overrightarrow{p},{\overrightarrow{p}}^{\text{'}})$ reaction at $E_0=172$ MeV and $\theta =6.3^{°}$ in comparison to theoretical predictions using QPM wave functions and models I (dotted lines), II (dashed lines), and III (solid lines) for the effective target-nucleon interaction.

Figure 3

Same as Fig. 2 for model III of the effective projectile-target interaction without (solid line) and with (dashed-dotted line) a quenching of the spin-isospin channel.

Figure 4

Comparison of measured and calculated spin-flip probabilities of the ${}^{58}\mathrm{Ni}$($\overrightarrow{p},{\overrightarrow{p}}^{\text{'}})$ reaction at $E_0=172$ MeV at $\theta =6.3^{°},9.6^{°}$, and $11.2^{°}$, using model III for the effective projectile-target interaction without (solid line) and with (dashed-dotted line) a quenching of the spin-isospin channel.