A spin polarized He\sp+ ion source has been developed to study the dynamics of ion-surface interactions. The He\sp+ ions are produced by Penning ionization in collisions between electron-spin-polarized He(2\sp3S) metastable atoms contained in a weak rf-excited discharge. The ions are extracted from the discharge and focused onto clean or adsorbate-covered surfaces using a series of electrostatic lenses. The impact energy can be varied from <10eV to ≥650eV and typical beam polarizations are 10-15%. Information about ion/surface interactions, and the dependence of those interactions on the incident ion energy, is obtained by measuring the energy distribution and polarization of electrons ejected from the surface as a result of Auger neutralization.