Nuclear Spectroscopic Studies with High-Energy Boron Ions

Abstract

High-energy boron beams have been used in studies of proton and deuteron transfer reactions involving a carbon target. These studies, involving examination of reactions leading to isolated states in the residual nuclei, were undertaken to obtain information on the transfer mechanism at high energies, and to ascertain the extent to which such reactions might serve as probes for certain one- and two-nucleon states in the residual nuclei involved. The proton transfer reactions ${\mathrm{C}}^{12}$(${\mathrm{B}}^{11}$, ${\mathrm{Be}}^{10}$)${\mathrm{N}}^{13}$ and ${\mathrm{C}}^{12}$(${\mathrm{B}}^{10}$, ${\mathrm{Be}}^{9}$)${\mathrm{N}}^{13}$, at bombarding energies of 115.5 and 105 MeV, respectively, are observed to populate only a few levels in ${\mathrm{N}}^{13}$. The first excited state, which is known to have a large proton width, is not one of these levels. It is suggested that this reflects an angular-momentum mismatch which acts to inhibit the $S$-wave proton transfer which would populate this state. The deuteron transfer reaction ${\mathrm{C}}^{12}$(${\mathrm{B}}^{11}$, ${\mathrm{Be}}^{9}$)${\mathrm{N}}^{14}$, at 115.5 MeV bombarding energy, is also observed to populate only a few levels in the residual nucleus ${\mathrm{N}}^{14}$. Arguments are presented favoring direct population of ${\mathrm{N}}^{14}$ levels having ${\mathrm{C}}^{12}$+${({d}_{\frac{5}{2}})}^{2}$ and ${\mathrm{C}}^{12}$+(${d}_{\frac{3}{2}}, {d}_{\frac{5}{2}}$) two-particle configurations. In particular, the observed strongly populated levels at approximately 9- and 13-MeV excitation have been tentatively identified as the $J=5$, $T=0$ and $J=4$, $T=0$ members of the above multiplets, respectively. The existing intermediate-coupling calculations pertaining to ${\mathrm{N}}^{14}$ are in excellent accord with such a description but suggest significant (${p}_{\frac{1}{2}}, {f}_{\frac{7}{2}}$) admixtures in the latter state. The angular distributions of the strong groups in all reactions are smoothly varying, exponential functions of angle. These have been fitted, in terms of a surface-diffuseness parameter, using a simple diffraction model. The diffuseness obtained is in excellent accord with other results in the same mass and energy range. By comparing the present data with those on other reactions involving the same incident systems, qualitative conclusions are drawn regarding fractional parentage in the incident systems. In both single- and two-nucleon situations, the experimental results are compared in detail with corresponding data from ${\mathrm{He}}^{3}$- and ${\mathrm{He}}^{4}$-induced reactions.