Complete momentum balance for single ionization of helium by fast ion impact: Experiment

The collision dynamics of He single ionization by 3.6 MeV/u Se28+ impact was explored using the reaction microscope of the Gesellschaft fur Schwerionenforschung, a high-resolution integrated multielectron recoil-ion momentum spectrometer. The complete three-particle final-state momentum distribution (nine Cartesian components p(i)) was imaged with a resolution of Delta p(i) approximate to +/-0.1 a.u. by measuring the three momentum components of the emitted electron and the recoiling target ion in coincidence. The projectile energy loss has been determined on a level of Delta E-p/E-p approximate to 10(-7) and projectile scattering angles as small as Delta theta approximate to 10(-7) rad became accessible. The experimental data which are compared with results of classical trajectory Monte Carlo calculations reveal an unprecedented insight into the details of the electron emission and the collision dynamics for ionization of helium by fast heavy-ion impact.