Polarization in the Elastic Scattering of Protons from Carbon and Nitrogen

The polarization of protons elastically scattered from nitrogen and carbon has been measured using double-scattering techniques. The polarization was determined for nitrogen at a scattering angle of 48° c.m. in the proton-energy interval 12.6 to 13.6 MeV. The polarization resulting from elastic proton scattering with nitrogen targets had a constant value of -0.60±0.10 in the incident proton-energy interval 8.2 to 11.8 MeV. The polarization from carbon, however, varied markedly with energy at most scattering angles. [Example: $P({50°}_{\mathrm{lab}},12.9\mathrm{} \mathrm{MeV})=-0.8\mathrm{}$, $P(50\mathrm{}°,13.2)=-0.4\mathrm{}$, and $P(50\mathrm{}°,13.5)=-0.7\mathrm{}$.] At numerous angles between 20° and 140°, polarization measurements from carbon covered the range of energies from 12.8 to 13.4 MeV. The angular distributions of polarization (and cross section) are in general quite sensitive to small changes in energy; the 12.95- and 13.25-MeV angular distributions even differ in shape significantly for $\theta >90\mathrm{}°$. The energy-averaged (12.8- to 13.4-MeV) angular distribution for the polarization of protons scattered from carbon was compared with optical-model calculations.