Polarization of Protons from theB10(He3, p)C12*(4.43−MeV)Reaction

Abstract

Proton polarizations were measured for the ${\mathrm{B}}^{10}({\mathrm{He}}^{3}, p){\mathrm{C}}^{12*}(4.43\ensuremath{-}\mathrm{MeV})$ reaction at ${\mathrm{He}}^{3}$ energies of 2.5 and 2.8 MeV. These measurements were made for twelve angles from 0 to 135\ifmmode^\circ\else\textdegree\fi{} at 2.5 MeV and for six angles from 15 to 75\ifmmode^\circ\else\textdegree\fi{} at 2.8 MeV. The measurements at 2.5 MeV show that the polarization reaches a minimum of -0.36\ifmmode\pm\else\textpm\fi{}0.07 at ${\ensuremath{\theta}}_{\mathrm{lab}}=15\ifmmode^\circ\else\textdegree\fi{}$, where the sign of the polarization follows the Basel convention. At larger angles the polarization fluctuates and generally decreases. It could not be determined whether the polarization changes sign or is zero at the back angles. The angular dependences of the polarizations at 2.8 MeV are similar to those obtained at 2.5 MeV, indicating a weak energy dependence in the energy range used. The weak energy dependence is consistent with an interpretation of the reaction in terms of a direct reaction mechanism or a compound-nucleus process in which only a few, very broad levels are involved. The polarizations were analyzed by scattering the protons from a plastic scintillator, using the known properties of the polarization of protons scattered by carbon. With the plastic scintillator, it was possible to reduce the backgrounds in the side detectors. This was done by identifying the scattered protons as coincidences between the second scatterer and pulses of the proper energy in the side detectors. Geometrical uncertainties obtained by machine calculations are included in the statistical uncertainties.