($p, \mathrm{pn}$) reactions induced by 17-MeV protons on 12 different nuclei are studied by coincidence detection and energy measurements of the emitted neutron and proton. Probabilities of exciting various final states and of ($p, p^{\prime }\gamma$) reactions (i.e., no neutron emission) are measured as a function of the energy of the emitted particles, and attempts are made to explain the results with a model assuming that these are ($p, p^{\prime }$) reactions followed by neutron boil-off. There are many disagreements with the predictions of this model, and many inconsistencies between results from the different nuclei under this interpretation. It is shown that including contributions from ($p, n$) reactions followed by proton boil-off does little to improve the situation. The results might be explained if both particles are emitted in a direct reaction, although there is difficulty with the simplest such reaction, a single collision knockout, in that there is poor correlation between states excited in these reactions and in pickup reactions such as ($p, d$).

• Received 10 November 1969

DOI:https://doi.org/10.1103/PhysRevC.1.1237