A method is developed for clearly distinguishing experimentally between ($p, 2p$) reactions which result from ($p, p^{\prime }$) reactions followed by proton boiloff, and those in which the two protons are both emitted within ∼${10}^{-22\mathrm{}}$ sec in a direct reaction (referred to as "double direct"). Measurements involving coincidence detection and energy measurements on the two protons emitted at equal angles on opposite sides of the beam (${\theta }_2={\theta }_1$, ${\phi }_2={\phi }_1+\pi$) indicate that at 17 MeV bombarding energy in the $A=50-65\mathrm{}$ region, the boiloff process is predominant with cross sections of the order of 1 mb for exciting ground states or low-lying excited states. The cross section for the double-direct process is not more than about 10 μb. A crude theoretical estimate indicates that this is about the correct order of magnitude.

NUCLEAR REACTION ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$, ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$, ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}(p, 2p)$, $E_p=17\mathrm{}$ MeV, exciting g.s., 1st excited; measured energy spectra, angular distributions, deduced cross sections for ($p, p^{\prime }$) followed by boiloff, and for completely direct reactions.

• Received 31 August 1976

DOI:https://doi.org/10.1103/PhysRevC.15.260