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 k₀=54.1^∘, k₁=+1.0^∘, k₂=+0.4^∘, respectively.