$\alpha$-particle optical potential tests below the Coulomb barrier

The results of two recent papers concerning $(\alpha ,\gamma )$ and $(\alpha ,n)$ reaction cross sections close to the reaction thresholds are discussed with regard to predictions of a recent $\alpha$-particle regional optical potential. It is found that the new measured cross sections are rather well described especially for the dominant reaction channels. Particular features of the $\alpha$-particle optical potential at energies below the Coulomb barrier explain the failure of a former regional potential obtained by analysis of $\alpha$-particle elastic scattering alone at higher energies. Additional limitations of statistical model calculations for minor reaction channels are also discussed.

Figure 1

Comparison of (a)–(c) calculated total $\alpha$-reaction cross sections using a former ROP [3] (dash-dotted curves) and parameters in Ref. [4] obtained above the Coulomb barrier height $B$, in MeV $(E>B)$, by elastic scattering analysis alone (dashed curve). Comparison of the measured cross sections for $(\alpha ,n)$ reaction on ${}^{92,94}\mathrm{Mo}$ nuclei [1], and $(\alpha ,\gamma )$ and $(\alpha ,p)$ reactions on ${}^{112}\mathrm{Sn}$ [1, 7], and calculated values using (a)–(c) ROP parameters at $E>B$ (dotted curves) and complete ROP [4] (solid), and (d)–(f) the complete ROP.

Figure 2

The same as in Fig. 1 but for the $(\alpha ,\gamma )$ reaction on (a,c) ${}^{117}\mathrm{Sn}$ [2] and (b,d) ${}^{118}\mathrm{Sn}$ [9] nuclei, as well as (a) ${}^{117}\mathrm{Sn}(\alpha ,p){}^{120}{\mathrm{Sb}}^m$ reaction [2] and calculations using ROP parameters established at $E>B$ (thin dotted curve) and complete ROP [4] (thin solid curve), and (c) both the total and isomeric state populations by the $(\alpha ,p)$ reaction (upper and lower dash-dotted curves, respectively).

Figure 3

Comparison of measured $(p,n)$ reaction cross sections and isomeric cross-section ratio for ${}^{121}\mathrm{Sb}$ target nucleus [15] and calculated values using: (a) proton global OMPs of Ref. [11] (dashed curves) and [16] (solid curves), and (b) the latter OMP for the proton reaction cross section (short-dotted curve); the $(p,n)$ total (solid curve), g.s. (dashed curve), and isomeric state (dash-dotted curve) population cross sections; and the $(p,\gamma )$ reaction (dash-dot-dotted curve) and $(p,p^{\text{'}})$ reaction (dotted curve) cross sections.

Figure 4

Comparison of $(\alpha ,\gamma )$, $(\alpha ,n)$, and $(\alpha ,p)$ reaction cross sections calculated by using NON-SMOKER [17] (dashed curves) and TALYS-1.0 [18] (dash-dotted curves) predictions and a local parameter analysis [4] (solid curves).