Evidence for Sequential Two-Body Decay in Three-Body Decay ofC12andB10

The reactions ${\mathrm{B}}^{11}(p, \alpha ){\mathrm{Be}}^8$ and ${\mathrm{Be}}^9(p, d){\mathrm{Be}}^8$ have been studied by employing monoenergetic protons, thin targets, and a low-background magnetic spectrometer to resolve the disintegration products. The continuum spectra of alpha and deuteron particles produced, respectively, in the reactions have been compared to the generalized density-of-states function of Phillips, Griffy, and Biedenharn and good fits have been obtained. The density function was calculated from the experimental ($\alpha , \alpha$) scattering phase shifts. The calculated $S$-wave density function for ${\mathrm{Be}}^8$ predicts a low-energy anomaly. This anomaly has been observed and confirms the assumption of the model used to calculate this spectral shape: three-body decay proceeding via a sequence of two-body decay modes.