Scattering of Protons by Hydrogen Near 18 Mev

The differential cross section for the scattering of 18.2±0.2-Mev protons by hydrogen has been measured over the angular range 30°-90° in the center-of-mass system. In order to reduce the over-all errors to less than 1 percent a 60-in. scattering chamber was used. Polyethylene, polystyrene, and nylon foils were used as scatterers while the proton-proton events were detected by observing coincidences between the scattered and recoil protons in anthracene photomultiplier counters. The incident proton beam was collimated to ±14 minutes of arc. Probable relative errors varied from 0.5 percent at 90° to about 1 percent at 30°, while the probable error in the absolute differential cross section at 90° is estimated to be 1 percent. The data show a significant deviation from pure $S$-wave scattering and are best fitted by taking $S$-, $P$-, and $D$-wave phase shifts to be $k_0=54.1\mathrm{}°$, $k_1=+1.0\mathrm{}°$, $k_2=+0.4\mathrm{}°$, respectively.