The polarized proton beam from the UCLA sector-focused cyclotron has been to measure the angular dependence of the polarization in elastic scattering of protons from oxygen at mean proton energies of 24.5, 27.3, 30.1, 34.1, 36.8, and 39.7 MeV. The polarized proton beam was produced by scattering the internal beam from a carbon scatterer. The different proton energies were attained by varying the thickness of the carbon vane and by degrading the external proton beam, using aluminum degraders. A calibration of the beam polarization for the various scatterers was obtained in a separate experiment. A disc of ice 0.032 in. thick by 1.25 in. diam was used as an oxygen target. Four NaI(Tl) integral line detectors were placed two on each side of the incident beam so that protons scattered to the left and to the right at two different angles could be counted at the same time. A solenoid magnet capable of rotating the direction of polarization by ±180° was used, allowing three independent measurements of the left-right asymmetry to be made at each angle. The data obtained for incident proton energies between 30 and 40 MeV exhibit a smooth energy behavior. The data at 24.5 and 27.3 MeV, however, suggest the presence of strong resonances which cause a drastic variation in the polarization angular distribution. A comparison with existing experimental data supports this explanation.

• Received 5 September 1967

DOI:https://doi.org/10.1103/PhysRev.167.915