(p, pn) and (p, 2p) Reactions ofCe142at Proton Energies from 0.4 to 3.0 Bev

Abstract

Cross sections are reported for ($p, \mathrm{pn}$) and ($p, 2p$) reactions of ${\mathrm{Ce}}^{142}$ with protons of 0.4, 1.0, 2.2, and 3.0 Bev. To evaluate the contribution of proton and neutron evaporation from excited ${\mathrm{Ce}}^{142}$ nuclei to the observed cross sections, this evaporation competition was studied by means of cross-section measurements on the reactions ${\mathrm{Ba}}^{138}(\ensuremath{\alpha}, n)$ and ${\mathrm{Ba}}^{138}(\ensuremath{\alpha}, p)$ with $\ensuremath{\alpha}$ particles of 19- to 40-Mev kinetic energy. The ratio $\frac{{\ensuremath{\sigma}}_{\ensuremath{\alpha},n}}{{\ensuremath{\sigma}}_{\ensuremath{\alpha},p}}$ is between 2.4 and 4.4 in this region as compared with a ratio of 1.58\ifmmode\pm\else\textpm\fi{}0.14 for $\frac{{\ensuremath{\sigma}}_{p,pn}}{{\ensuremath{\sigma}}_{p,2p}}$ at 0.4 Bev. It is concluded that at this energy the ($p, \mathrm{pn}$) and ($p, 2p$) reactions proceed at least partially by a pure knock-on mechanism. This conclusion is supported by comparison of the data with recent Monte Carlo calculations of intranuclear cascades. With increasing proton energy both ${\ensuremath{\sigma}}_{p,2p}$ and ${\ensuremath{\sigma}}_{p,pn}$ are found to decrease, the former more rapidly than the latter. This energy dependence is discussed in terms of the elementary nucleon-nucleon cross sections. The Monte Carlo calculations mentioned agree within their rather poor statistical accuracy with the measured cross-section ratios and with the energy dependence of the cross sections, but predict cross-section values about a factor of three too small.