Measurements of the elastic differential cross section for the scattering of protons by helium have been made at 12 energies between 11.4 Mev and 18 Mev. Ten scattering angles were used spaced at 15° intervals from 30° to 165° in the laboratory system; however, not all the angles were used at each energy. Standard gas-scattering techniques were employed. Scattered particles were detected by a scintillation counter and recorded on a 20-channel pulse-height analyzer. At nine of the scattering angles (165° excluded), smoothed curves of the cross section versus energy were plotted and values taken from these curves were analyzed in terms of $S$- and $P$-wave phase shifts. Two separate sets of $S$ and $P$ phase shifts intersecting at about 13 Mev were found. Least-squares fits are given for the solutions which are a continuation of phase-shift analyses at lower energies. Attempts to include $D$ waves in the fits failed. There is evidence that $D$ phase shifts remain less than about 8° up to 16 Mev; however, at 18 Mev it appears that some $D$ wave may be required. Rough agreement with current polarization experiments is cited.

• Received 6 August 1957

DOI:https://doi.org/10.1103/PhysRev.108.1000