Double Stripping: (He3,n) Reaction

Abstract

The two-nucleon stripping reaction is examined in detail, with particular reference to the (${\mathrm{He}}^3$, $n$) reaction. Three models are studied and compared: (1) the plane-wave Born approximation, (2) the distorted-wave Born approximation, and (3) a simple diffraction model. Zero-range approximations are not assumed a priori. For (1) and (2), the wave functions of the two captured nucleons are taken to be eigenstates of an infinite harmonic oscillator, the strength of which is adjusted to reproduce single-particle eigenfunctions of a finite Saxon well in regions close to the nuclear surface. The first model is primarily employed to show that the modulation of the angular distribution due to the structure of ${\mathrm{He}}^3$ is also sensitive to the form and range of the stripping interaction. Model (2) is used to calculate absolute differential cross sections to various final states, in particular for ${\mathrm{C}}^{12}$, ${\mathrm{O}}^{16}$, Ni, and Sn targets with 20-MeV incident ${\mathrm{He}}^3$ ions. Comparison with experimental data is made where available and agreement is found. To further such comparisons we also compute summed cross sections to several low-lying states of the final nucleus. Spectroscopic weights are obtained for pure and mixed configurations of single-particle wave functions. Model (3) provides insight into the dominant features of the experimental and calculated [model (2)] differential cross sections. These are: (a) a strong forward peaking of the distribution especially for spin 0 to 0 transitions, but also for summed cross sections, (b) an angular distribution for such sums that is roughly independent of the atomic weight of the target nucleus, and (c) an enhancement of cross sections to higher spin states (≈ 3 or 4) of final nuclei. These features are not reproduced with model (1).