Coincidence Studies of theNi58(p, 2p)Reaction

Abstract

The ${\mathrm{Ni}}^{58}(p, 2p)$ reaction, by far the predominant reaction in that nucleus, was studied by detecting the two outgoing protons in coincidence. Measurements were made of the energy spectra of all protons from the reaction, of the spectrum of the sum of the energies of the two outgoing protons, and of the angular correlations of the outgoing protons with each other and with the incident proton. The results indicate quite conclusively that the preponderance of ($p, 2p$) over ($p, \mathrm{pn}$) reactions in ${\mathrm{Ni}}^{58}$ is not due to the relative level densities of the final nuclei, the ineffectiveness of Coulomb barriers, or a high emission energy of the "first" proton leaving emission of a neutron energetically forbidden. Other possible explanations are considered.There is strong evidence that the ($p, 2p$) reaction mechanism is predominantly a direct one in which the two protons are "knocked-out" simultaneously.