Measurements and Distorted-Wave Born-Approximation Analyses of Some 13.9-MeV Differential Cross Sections for theN14(He3, α)N13Reactions

The (${\mathrm{He}}^3$, $\alpha$) differential cross sections leading to the ground and 2.367-, (3.51+3.56)-, 6.38-, and (7.18+7.42)-MeV states of ${\mathrm{N}}^{13}$ have been measured at an incident ${\mathrm{He}}^3$ energy of 13.9 MeV using silicon surface-barrier detectors and a conventional electronic spectrometer system. Energy spectra were accumulated at 2.5° intervals over a laboratory angular range 17.5°-90° and at 5° intervals from 90° to 170°. The experimental differential (${\mathrm{He}}^3$, $\alpha$) cross sections corresponding to states in ${\mathrm{N}}^{13}$ at 0, 2.367, 6.38, and (7.18+7.42) MeV exhibit a pronounced oscillatory structure, suggesting that a direct-reaction mechanism is dominant. The composite cross section corresponding to the transitions leading to the (3.51+3.56)-MeV doublet has a somewhat washed-out structure. All angular distributions display a definite forward-angle peaking, and those leading to the ground and 2.367- and (3.51+3.56)-MeV states of ${\mathrm{N}}^{13}$ show evidence of strong backward-angle peaking. The transitions leading to the odd-parity states in ${\mathrm{N}}^{13}$ appear to be considerably enhanced relative to those leading to the even-parity states. The angular distributions corresponding to the transitions to the ground and 2.367- and 6.38-MeV states have been analyzed within the framework of the zero-range distorted-wave theory using a simple knockout model. The use of cutoff radii equal to or slightly larger than the nuclear radius was necessary in order to obtain reasonably good representations of the experimental data.