Analysis of the one-neutron transfer to ${}^{16}\mathrm{O},{}^{28}\mathrm{Si}$, and ${}^{64}\mathrm{Ni}$ induced by the $\left({}^{18}\mathrm{O},{}^{17}\mathrm{O}\right)$ reaction at 84 MeV

Background: Recently, a systematic exploration of two-neutron transfer induced by the $\left({}^{18}\mathrm{O},{}^{16}\mathrm{O}\right)$ reaction on different targets has been performed. The high-resolution data have been collected at the MAGNEX magnetic spectrometer of the INFN-LNS Laboratory in Catania and analyzed with the coupled reaction channel (CRC) approach. The simultaneous and sequential transfers of the two neutrons have been considered under the same theoretical framework without the need for adjustable factors in the calculations.

Purpose: A detailed analysis of the one-neutron transfer cross sections is important to study the sequential two-neutron transfer. Here, we examine the $\left({}^{18}\mathrm{O},{}^{17}\mathrm{O}\right)$ reaction on ${}^{16}\mathrm{O},{}^{28}\mathrm{Si}$, and ${}^{64}\mathrm{Ni}$ targets. These even-even nuclei allow for investigation of one-neutron transfer in distinct nuclear shell spaces.

Method: The MAGNEX spectrometer was used to measure mass spectra of ejectiles and extract differential cross sections of one-neutron transfer to low-lying states. We adopted the same CRC formalism used in the sequential two-neutron transfer, including relevant channels and using spectroscopic amplitudes obtained from shell-model calculations. We also compare with the one-step distorted-wave Born approximation (DWBA).

Results: For the ${}^{18}\mathrm{O}+{}^{16}\mathrm{O}$ and the ${}^{18}\mathrm{O}+{}^{28}\mathrm{O}$ systems, we used two interactions in the shell model. The experimental angular distributions are reasonably well reproduced by the CRC calculations. In the ${}^{18}\mathrm{O}+{}^{64}\mathrm{Ni}$ system, we considered only one interaction, and the theoretical curve describes the shape and order of magnitude observed in the experimental data.

Conclusions: Comparisons between experimental DWBA and CRC angle-integrated cross sections suggest that excitations before or after the transfer of a neutron are relevant in the ${}^{18}\mathrm{O}+{}^{16}\mathrm{O}$ and ${}^{18}\mathrm{O}+{}^{64}\mathrm{Ni}$ systems.

Figure 1

Typical spectra for particle identification performed at the Focal Plane Detector of the MAGNEX spectrometer. The atomic numbers of ejectiles are selected in a $\mathrm{\Delta }E\text{−}E$ spectrum [see (a)]. The isotopic identification is performed exploring the correlation between horizontal position and residual energy [see (b)]. A graphical selection on oxygen in (a) removes other atomic species and ${}^{18,17,16}{\mathrm{O}}^{8+}$ [identified in (b)], and a small fraction of ${}^{18,17,16}{\mathrm{O}}^{7+}$ isotopes are clearly seen in red.

Figure 2

Excitation energy spectra of (a) ${}^{17}\mathrm{O}$, (b) ${}^{29}\mathrm{Si}$, and (c) ${}^{65}\mathrm{Ni}$ residual nuclei. Backgrounds due to contamination in the targets are negligible under the peaks of interest and are not shown in the spectra. The blue lines are set at a one-neutron emission threshold energy for each nucleus. Transfer cross sections have been extracted for the numbered peaks indicated in each spectrum.

Figure 3

Coupling scheme for projectile overlaps considered in this paper. Continuous and dashed lines correspond to direct and two-step transitions.

Figure 4

Experimental angular distribution of the cross sections for the one-neutron transfer in the ${}^{16}\mathrm{O}({}^{18}\mathrm{O},{}^{17}\mathrm{O}){}^{17}\mathrm{O}$ reaction compared with theoretical predictions. The reaction channels are identified on the graph. The solid blue and dashed red curves correspond to CRC calculations using SAs derived with the ZBM and PSDMOD interactions, respectively.

Figure 5

Angular distributions of the cross sections for the ${}^{28}\mathrm{Si}({}^{18}\mathrm{O},{}^{17}\mathrm{O}){}^{29}\mathrm{Si}$ reaction leading to the population of ${}^{29}\mathrm{Si}$ in the ground state (top); (c) ${}^{17}\mathrm{O}$ ejectile in the $1/2^{+}$ state at 0.87 MeV (middle), and ${}^{28}\mathrm{Si}$ in the $3/2^{+}$ state at 1.27 MeV (bottom). SAs for ${}^{17,18}\mathrm{O}$ derived in the shell model using the PSDMOD calculation. In the ${}^{28,29}\mathrm{Si}$ cases, two interactions have been considered: the PSDMOD and the PSDMWKPN.

Figure 6

Angular distributions of the one-neutron transfer cross sections leading to the low-lying states in ${}^{65}\mathrm{Ni}$. At the top, summed cross sections for transfers to the g.s., 0.06- and 0.31-MeV states in the ${}^{65}\mathrm{Ni}$ nucleus. Bottom, summed cross sections for the 0.69-, 1.02-, 1.14-, and 1.27-MeV states in ${}^{65}\mathrm{Ni}$ and 0.87 MeV in the ${}^{17}\mathrm{O}$ ejectile. SAs for ${}^{17,18}\mathrm{O}$ and ${}^{64,65}\mathrm{Ni}$ derived in the shell model using the PSDMOD and BJUFF interactions, respectively.