Proton Emission in 42-MeV Alpha-Particle Bombardments of Several Elements

Measurements have been made of the energy spectra, angular distributions, and absolute cross sections of protons emitted from bombardments of ${\mathrm{Co}}^{59}$, ${\mathrm{Ni}}^{58}$, ${\mathrm{Ni}}^{60}$, ${\mathrm{Ni}}^{62}$, ${\mathrm{Cu}}^{63}$, ${\mathrm{Cu}}^{65}$, Nb, Rh, Pd, and Pt targets by 42-MeV alpha particles. A $\frac{\mathrm{dE}}{\mathrm{dX}}-E$ scintillation telescope was used in conjunction with an $x$, $y$ oscilloscope to detect and identify protons in the energy range from 2 to 40 MeV. The data were compared with predictions of the statistical model of nuclear reactions. A calculation was made of the expected proton energy spectra based on this model. The cascade was restricted to neutron and proton emission only, and a level density of the form $\frac{\left\{\exp 2{\left[a\right(U-\delta \left)\right]}^{\frac{1}{2}}\right\}}{{(U-\delta )}^2}$ was used. Except for Pt, the calculated and experimental energy spectra matched in slope over a relatively wide intermediate-energy region with the observed spectrum, exceeding the calculated spectrum in both the lowest and highest energy regions. The lowest energy protons were assumed to be caused by compound-nuclear events and the data were separated into compound-nuclear and non-compound-nuclear portions. It was found that the compound-nuclear portions agree well with expectations of the statistical model for yields, spectra, and angular distributions, and they account for 90% of the proton yield for targets in the Ni region, 65% of the proton yield for targets in the Rh region, and probably less than 6% of the proton yield for Pt. The non-compound-nuclear component exhibits a relatively constant yield of ≈85 mb for all the targets studied.