(16O,14C) reaction on some even N=28 isotones.

Abstract

The two-proton stripping reaction ${(}^{16}$O${,}^{14}$C) has been measured on some of the even N=28 isotones: $^{48}\mathrm{Ca}$, $^{52}\mathrm{Cr}$ at 160 MeV and $^{50}\mathrm{Ti}$, $^{54}\mathrm{Fe}$ at 150 MeV bombarding energy. States of excitation up to 10 MeV have been extracted over an angular range 4\ifmmode^\circ\else\textdegree\fi{}--10\ifmmode^\circ\else\textdegree\fi{} in the center-of-mass system. The angular distributions have been compared to transfer calculations that consist of both the simultaneous and successive transfer processes and were performed in exact finite range. Only the simple, (1${f}_{7/2}$${)}^{n}$ dominated states have been analyzed to investigate whether this reaction mechanism can account for the data. The absolute magnitude of the $^{48}\mathrm{Ca}$${(}^{16}$O${,}^{14}$C) $^{50}\mathrm{Ti}$ ground-state reaction has been reproduced. However, the experimental and theoretical uncertainties are larger than the sensitivity to different structure descriptions of the target/residual nuclei. Therefore, we have not been able to probe the pairing correlations in the ground state of $^{50}\mathrm{Ti}$. The calculations fail to reproduce the magnitude of the transitions to other states in $^{50}\mathrm{Ti}$. Similar problems occurred for the other reactions, leading to $^{52}\mathrm{Cr}$, $^{54}\mathrm{Fe}$, and $^{56}\mathrm{Ni}$. The discrepancy ranges from a factor of 2 to nearly 30. In addition, there are phase differences between the calculations and the measured cross sections. Some systematics of the disagreement are investigated. It is suggested that the simultaneous/successive mechanism can account for the data when the transition is kinematically well matched. In cases of poor matching, inelastic/transfer mechanisms may be kinematically enhanced and contribute to the cross section with significant strength.