C12(p,2p)B11Reaction at 50 MeV

Abstract

The ${\mathrm{C}}^{12}\mathrm{}(p,2p)\mathrm{}{\mathrm{B}}^{11}$ reaction has been studied at a bombarding energy of 50.0±0.2 MeV with an energy resolution of 300 keV. Transitions were observed to the ground state and to the 2.14-, 4.46-, 5.04-, and 6.76-MeV excited states of ${\mathrm{B}}^{11}$. Angular correlation measurements have been made in various coplanar geometrical arrangements. In the symmetric geometry, where the protons are detected at equal angles on either side of the incident beam direction, the angular correlation was measured from 15° to 115°. In an asymmetric geometry in which one detector was fixed at 30°, measurements were made as the other detector was moved between 15° and 100° on the other side of the beam direction. Both of the angular correlations are characterized by a general rise in the forward direction, modulated by a diffractionlike structure, when only those events are selected in which the energies of the selected protons are equal. The results of a distorted-wave analysis are presented and discussed. The formation of the 4.46-MeV (${\frac{5}{2}}^{-}$) and 6.76-MeV (${\frac{7}{2}}^{-}$) states is discussed in terms of the ejection of a proton from the $1f$ shell in ${\mathrm{C}}^{12}$ and, more attractively, in terms of a two-stage process involving both the ejection of a $1p$-state proton and a core excitation.