Evidence for Compound Nucleus Formation Using (p, p′) and (α, p) Scattering in Nickel

Spectra for ($p, p^{\prime }$) and ($\alpha , p$) reactions have been obtained by bombarding nickel targets with the beam of the Livermore 90-inch cyclotron and magnetically analyzing protons emitted at 135°. These reactions were studied for several energies of incident protons between 7.8 and 11.4 Mev, and incident alphas between 9.65 and 12.8 Mev. When the differential scattering cross section is divided by the emitted channel energy and the black nucleus cross section for protons, results are obtained for different incident proton energies which have the same relative shape when plotted vs excitation energy. This is strong evidence for formation of compound nucleus in these reactions. A large peak is observed in the spectrum at 4.75 Mev, an excitation energy where the level density is sufficiently high that it is difficult to attribute this peak to a single level. An anomalous peak at about this energy has been previously observed for 23-Mev ($p, p^{\prime }$) scattering and 30-Mev ($\alpha , {\alpha }^{\prime }$) scattering on nickel targets by Cohen, and Sweetman and Wall. Results obtained for the ($\alpha , p$) spectrum are in good agreement with predictions of the statistical model of the compound nucleus assuming a level density of the form $\exp \left[2\mathrm{}{\mathrm{}\left(\mathrm{aE}\right)\mathrm{}}^{\frac{1}{2}}\right]$.