B10-induced2nand2ptransfer reactions on light targets

Abstract

A systematic study is made of 100 MeV $^{10}\mathrm{B}$-induced $2n$ and $2p$ transfer reactions on light targets of $^{12}\mathrm{C}$, $^{14}\mathrm{N}$, and $^{16}\mathrm{O}$. These reactions are seen to selectively populate only a few states in the residual nuclei, showing them to be useful for studying states of particular structures. Known states with ${({p}_{\frac{1}{2}}{d}_{\frac{5}{2}})}_{3}$- and $({d}_{\frac{5}{2}})_{}^{2}{}_{{4}^{+}}{}^{}$ structures are strongly populated in the $T=1$ mass-14 nuclei. The known $({d}_{\frac{5}{2}})_{}^{2}{}_{{4}^{+}}{}^{}$ states in the $T=1$ mass-18 nuclei are also strongly populated. The lowest ${2}^{+}$ states (also of a $d_{\frac{5}{2}}^{}{}_{}{}^{2}$ nature) in these latter nuclei are populated more weakly. Exact finite-range distorted-wave Born-approximation calculations, assuming a cluster transfer of the two neutrons or protons, are presented for the strongly populated levels in the mass-14 and -18 residual nuclei, and for the ${2}^{+}$ level in $^{18}\mathrm{O}$. With the exception of this ${2}^{+}$ state and the unbound ${4}^{+}$ state in $^{14}\mathrm{O}$, the shapes of the angular distributions are well fitted by the cluster approximation. The distorted-wave Born-approximation normalizations to the data are compared to cluster spectroscopic factors calculated from shell model wave functions for the various states involved. In most cases, the extracted factors agree with the calculated spectroscopic factors to within a factor of 3. This agreement suggests that the reaction mechanism is predominantly a one-step transfer of a $T=1$, $S=0$ pair of neutrons or protons. The known structures of the strongly populated states in the mass-14 and -18 nuclei can be used to interpret newly observed states in the mass-16 spectra, in which there are two groups of strongly populated levels in each nucleus. The doublet in the low excitation region corresponds to the known ${2}^{\ensuremath{-}}$ and ${3}^{\ensuremath{-}}$ states presumably populated through the transfer of the nucleon pair into a ${({p}_{\frac{1}{2}}{d}_{\frac{5}{2}})}_{3}$- configuration coupled to the $^{14}\mathrm{N}_{1+}$ target core. The higher group of states is predicted to arise from the transfer of the nucleon pair into a $({d}_{\frac{5}{2}})_{}^{2}{}_{{4}^{+}}{}^{}$ configuration coupled to the ${1}^{+}$ core. The results of a Bansal-French-Zamick weak coupling model calculation for the center of gravity of the triplet of states from this $({d}_{\frac{5}{2}})_{}^{2}{}_{{4}^{+}}{}^{}$ configuration in the $T=1$ mass-16 nuclei are presented. These are seen to be in agreement with the observed energies of the high excitation peaks in the data.[NUCLEAR REACTIONS $^{12}\mathrm{C}$, $^{14}\mathrm{N}$, $^{16}\mathrm{O}$($^{10}\mathrm{B}$, $^{8}\mathrm{Li}$), $E=100$ MeV; $^{12}\mathrm{C}$, $^{14}\mathrm{N}$, $^{16}\mathrm{O}$($^{10}\mathrm{B}$, $^{8}\mathrm{B}$), $E=100$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$; DWBA analysis; extracted and calculated $2n$ and $2p$ spectroscopic factors; weak coupling model predictions.]