Target-Excitation Effects in Stripping Reactions

Target-excitation effects are studied in ($d,p$) and ($d,n$) reactions using simple microscopic models. These effects occur when the outgoing nucleon excites the target nucleus; the stripped nucleon then couples with this excited state to form the final nuclear state. By choosing the optical potential for elastic scattering of the outgoing nucleon by the target nucleus in its ground state as the generator of the final-state distorted waves, and making the usual assumptions of the distorted-wave model, the distorted-wave amplitude separates into the standard distorted-wave Born-approximation amplitude plus one involving target excitation alone. Assuming a shell-model description of the target and residual nuclei and using two-body forces to describe the interaction between the outgoing nucleon and target nucleus, an angular-momentum decomposition of the target-excitation amplitude is made. Numerical estimates of the effect of target excitation are obtained using the following assumptions for the ${\mathrm{Ca}}^{40}\mathrm{}(d,p)\mathrm{}{\mathrm{Ca}}^{41}$ reaction: the deuteron is a point particle; the two-body force has a Gaussian shape; the target nucleus is doubly magic; the final nucleus is doubly magic plus one open shell; the single-particle states are harmonic-oscillator states; both the real and imaginary parts of the deuteron and proton optical potentials have a Saxon-Woods form factor (volume absorption). Results are obtained for various oscillator strengths and well parameters. Except for certain cases, the effects of target excitation are found to be small. Angular-correlation measurements are discussed as a possible means for detecting the presence of nonnegligible target-excitation effects.