Excitation Functions of (p, 2 Nucleon) Reactions

Excitation functions for the ($p, \mathrm{pn}$) reaction have been determined in the energy range 250 Mev to 440 Mev for the target nuclei ${\mathrm{As}}^{75}$, ${\mathrm{Br}}^{81}$, ${\mathrm{Zr}}^{96}$, ${\mathrm{I}}^{127}$, ${\mathrm{Ce}}^{142}$, ${\mathrm{W}}^{186}$, and ${\mathrm{Re}}^{187}$. Both isomer products were determined in the case of the ${\mathrm{Br}}^{81}(p, pn){\mathrm{Br}}^{80}$ reaction. Also, excitation functions were determined for the ($p, 2p$) reaction on ${\mathrm{Zr}}^{96}$, ${\mathrm{Ce}}^{142}$, and ${\mathrm{W}}^{186}$ and for the ($p, 2n$) reaction on ${\mathrm{Zr}}^{96}$. All cross sections were measured relative to the ${\mathrm{Al}}^{27}(p, 3pn){\mathrm{Na}}^{24}$ excitation function. The ($p, \mathrm{pn}$) excitation functions are only moderately sensitive to energy showing an increase by about 30% for iodine, 20% for arsenic and cerium, and a 12% decrease for zirconium. The remaining excitation functions are flat. The ratio of ${\sigma }_{p,pn}$ to ${\sigma }_{p,2p}$ is 1.62±0.09, for the three targets measured, at 440 Mev. The various mechanisms for the production of reactions of this type are examined in the light of present understanding. The suggestion is made that, despite the relative insensitiveness of these excitation functions to energy, ($p, \mathrm{pn}$) and ($p, 2p$) reactions may take place by more than one mechanism in this energy region. A comparison is made with the results of recent Monte Carlo nuclear cascade calculations applied to calculation of ($p, \mathrm{pn}$) reaction excitation functions.