A survey of the differential cross sections for the elastic scattering of protons has been made for protons of 31.5, 20, and 14.5 Mev. The angular distribution shows well-developed maxima and minima only for nuclei of intermediate atomic weight. For heavy nuclei, the diffraction effect is destroyed by the Coulomb scattering. With 31.5-Mev protons, the first minimum disappears for nuclei heavier than Zr; with 20-Mev protons, for nuclei heavier than V. In light nuclei, the maxima and minima are progressively obliterated as the mass number is reduced and the energy is increased. In the main, the angular distribution changes smoothly from one nucleus to another, the cross sections at the maxima increasing as the fourth power of the nuclear radius. However, these cross sections are not proportional to the energy, as would be expected from elementary diffraction theory. For intermediate nuclei, these cross sections are nearly independent of the energy; for nuclei from O to Mg they rise to a maximum near 20 Mev, and for light nuclei, they fluctuate in a less regular manner.

• Received 8 May 1956

DOI:https://doi.org/10.1103/PhysRev.103.975