EXCITATION AND IONIZATION-EXCITATION OF HELIUM FOLLOWING ELECTRON AND PROTON IMPACT: A POLARIZATION STUDY H. Merabet*, A. Siems#, M. Bailey&, R. Bruch*, A. G. Trigueiros# *Department of Physics, University of Nevada Reno, Reno NV 89557 USA #Quantum Electronic Department, Physics Institute- UNICAMP, Campinas, Brazil &Atmospheric Science Center, Desert Research Institute (DRI), Reno NV 89506 USA New experimental results are presented on measurements of the degree of linear polarization for excitation and ionization-excitation of He following proton impact. In particular, polarization measurements for He (1snp) 1P0, He+ (2p) 2P0, and He+ (3p) 2P0 states with transition wavelengths of 51.7 to 58.4 nm, 30.4 nm, and 25.6 nm, respectively, have been obtained for proton impact energies ranging from 100 keV to 1 MeV. Furthermore, these results are compared with recent polarization measurements following electron impact on He for the same range of velocities.