At an incident proton bombarding energy of 6.5 Mev, angular correlations have been measured between protons scattered inelastically from various even-even nuclei and the decay gamma rays from the first excited states of these nuclei. Among the angular correlation experiments reported are ${\mathrm{C}}^{12}(p, p^{\prime }\gamma )$ 4.4 Mev, ${\mathrm{Ne}}^{20}(p, p^{\prime }\gamma )$ 1.63 Mev, ${\mathrm{Si}}^{28}(p, p^{\prime }\gamma )$ 1.78 Mev, and ${\mathrm{S}}^{32}(p, p^{\prime }\gamma )$ 2.25 Mev, which were done for proton detector angles of 60°, 90°, and 120°. The measured angular correlation functions are all of the form $A+B\left[{sin}^{2}2\right(\theta -{\theta }_0\left)\right]$, where ${\theta }_0$ is the axis of symmetry. None of the symmetry directions agreed with predictions of the simple direct-reaction theories. However, the symmetry direction for the correlation functions changed with proton detector angle for the experiments on ${\mathrm{C}}^{12}$, ${\mathrm{Ne}}^{20}$, and ${\mathrm{S}}^{32}$; for the experiment of ${\mathrm{Si}}^{28}$ the angular correlation functions were symmetric about 90°, independent of proton detector angle. The results of the angular correlation experiments appear to be consistent with a collective interaction involved in these direct-type reactions rather than a nucleon-nucleon type collision at the nuclear surface.

• Received 4 December 1959

DOI:https://doi.org/10.1103/PhysRev.118.1237