Examination of the influence of transfer channels on the barrier height distribution: Scattering of ${}^{20}\mathrm{Ne}$ on ${}^{58}\mathrm{Ni},{}^{60}\mathrm{Ni}$, and ${}^{61}\mathrm{Ni}$ at near-barrier energies

Background: It was suggested that the shape of the barrier height distribution can be determined not only by strong reaction channels (collective excitations) but also by weak channels such as transfers and/or noncollective excitations.

Purpose: The study of the barrier height distributions for the ${}^{20}\mathrm{Ne}+{}^{58,60,61}\mathrm{Ni}$ systems requires information on transfer cross sections at near-barrier energies.

Methods: A measurement of the cross sections for various transfer channels at a backward angle (142 degrees), at a near-barrier energy was performed. Identification of products was based on time-of-flight and $\mathrm{\Delta }E\text{−}E$ methods. A measurement of the angular distribution of $\alpha$ stripping in the ${}^{20}\mathrm{Ne}+{}^{61}\mathrm{Ni}$ system was performed using a gas $\mathrm{\Delta }E\text{−}E$ telescope.

Results: For all three systems studied: ${}^{20}\mathrm{Ne}+{}^{58}\mathrm{Ni},{}^{60}\mathrm{Ni}$, and ${}^{61}\mathrm{Ni}$ total (sum of all transfer channels) cross sections are similar and dominated by $\alpha$ stripping.

Conclusions: The results, as well as coupled reaction channel calculations, suggest that transfer is not responsible for smoothing the barrier height distribution in ${}^{20}\mathrm{Ne}+{}^{61}\mathrm{Ni}$, supporting the hypothesis that barrier distribution shapes are influenced by noncollective excitations.

Figure 1

Schematic view of experimental setup (a detailed description is given in the text).

Figure 2

Theoretical predictions of angular distribution of one- and two-neutron pickup for the ${}^{20}\mathrm{Ne}+{}^{61}\mathrm{Ni}$ reaction at an energy of 51 MeV. For $1n$ pickup calculations were performed with the code fresco [53] (results in mb/sr), for $2n$ pick-up with dwuck5 using the NRV system [54] (only pickup to the ground state was taken into account; the results are in arbitrary units because the spectroscopic factors are not known).

Figure 3

Angular distribution of ${}^{16}\mathrm{O}$ resulting from ${}^{20}\mathrm{Ne}$ interacting with ${}^{61}\mathrm{Ni}$ target at an energy $E_{\mathrm{lab}}=51$ MeV (experimental data).

Figure 4

The raw $\mathrm{\Delta }E\text{−}E$ spectrum for ${}^{20}\mathrm{Ne}+{}^{61}\mathrm{Ni}$ registered at ${142}^{\circ }$ (in the laboratory system).

Figure 5

The raw $E$-TOF results for (a) ${}^{20}\mathrm{Ne}+{}^{58}\mathrm{Ni}$ and (b) ${}^{20}\mathrm{Ne}+{}^{61}\mathrm{Ni}$ backscattered ions were registered at ${142}^{\circ }$ (in the laboratory system).

Figure 6

(a) $Q_{gg}$ and (b) $Q_{\mathrm{eff}}$ values for possible transfer channels in the ${}^{20}\mathrm{Ne}+{}^{58,60,61}\mathrm{Ni}$ systems leading to products with masses observed in the experiment.

Figure 7

(a) Contributions of different transfer channels to the quasi-elastic scattering at ${142}^{\circ }$ in the laboratory system and (b) the corresponding differential cross sections for ${}^{20}\mathrm{Ne}+{}^{58,60,61}\mathrm{Ni}$. Data for ${}^{20}\mathrm{Ne}+{}^{90}\mathrm{Zr}$ at $E_{\text{cms}}\simeq 51$ MeV [42] are also shown.

Figure 8

The $Q$ spectrum calculated for 51 MeV ${}^{20}\mathrm{Ne}$ on ${}^{61}\mathrm{Ni}$. See details in the text.

Figure 9

Barrier height distribution calculated with the fresco code. Solid line is for only collective channels taken into account, dashed line is for $1n$ transfer also included.