Scattering of 10-Mev Protons on Carbon and Magnesium

Abstract

In order to study the mechanism of excitation of nuclear levels by inelastic scattering, a scattering chamber of 36-inch diameter was constructed. The deflected beam of the Berkeley 60-inch cyclotron was brought out of the shielding by means of strong focusing magnets. Particles from the nuclear reactions were detected by either of two systems, a quadruple proportional-counter telescope, or a coincidence crystal spectrometer. Energy resolution was of the order of 2.5 percent. The angular distribution of protons from the reactions $C^{12}(p, p^{\prime }){\mathrm{C}}^{12*}$, $Q=-4.43\mathrm{}$ Mev, and ${\mathrm{Mg}}^{24}(p, p^{\prime }){\mathrm{Mg}}^{24*}$, $Q=-1.38\mathrm{}$ Mev, were found to be peaked in the forward direction. Since the compound nucleus is excited to about 13 Mev, where the level density is expected to be high and the statistical theory of the nucleus should hold, it is proposed that two processes of excitation occur. One, the formation of the compound nucleus and its subsequent decay—symmetrically about 90°; two, direct collision of the incident proton with a nucleon on the surface shell of the nucleus. The elastic scattering of protons on the above nuclei was also studied and interference maxima were found. Three new levels are believed to have been confirmed in magnesium.