Be9(p, pα)He5Reaction at 57 MeV

Abstract

The ${\mathrm{Be}}^{9}(p, p\ensuremath{\alpha}){\mathrm{He}}^{5}$ reaction was studied using 57-MeV protons from the Oak Ridge isochronous cyclotron. The correlated energies of both the emitted protons and $\ensuremath{\alpha}$ particles were measured at detection angles (${\ensuremath{\theta}}_{p}, {\ensuremath{\theta}}_{\ensuremath{\alpha}}$) of (94\ifmmode^\circ\else\textdegree\fi{}, -35.3\ifmmode^\circ\else\textdegree\fi{}), (105\ifmmode^\circ\else\textdegree\fi{}, -30\ifmmode^\circ\else\textdegree\fi{}), and (116\ifmmode^\circ\else\textdegree\fi{}, -25.1\ifmmode^\circ\else\textdegree\fi{}), where the detectors were coplanar with the beam. In addition, an angular correlation was measured by fixing ${\ensuremath{\theta}}_{p}$ at 105\ifmmode^\circ\else\textdegree\fi{} and varying ${\ensuremath{\theta}}_{\ensuremath{\alpha}}$ from -21\ifmmode^\circ\else\textdegree\fi{} to -39\ifmmode^\circ\else\textdegree\fi{} in 3\ifmmode^\circ\else\textdegree\fi{} steps. The data for the reaction leading to the ground state of ${\mathrm{He}}^{5}$ were found to be consistent with quasifree scattering of the incident protons by $S$-state $\ensuremath{\alpha}$-particle clusters in ${\mathrm{Be}}^{9}$. Analysis in terms of a plane-wave impulse approximation yields a momentum density distribution for the struck $\ensuremath{\alpha}$ particles which has a half-width of 0.27 ${\mathrm{F}}^{\ensuremath{-}1}$, and a probability of finding an $\ensuremath{\alpha}$-particle cluster in ${\mathrm{Be}}^{9}$ of ${0.25}_{\ensuremath{-}0.12}^{+0.25}$.