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Kinematically complete study on Positron impact ionization of Helium


Holzwarth,  Marco
Division Prof. Dr. Joachim H. Ullrich, MPI for Nuclear Physics, Max Planck Society;

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Holzwarth, M. (2010). Kinematically complete study on Positron impact ionization of Helium. Diploma Thesis, Ruprecht-Karls Universität, Heidelberg.

Cite as: http://hdl.handle.net/11858/00-001M-0000-0011-7263-F
Within this work presented here, single ionisation of helium by impact of 80eV positrons was studied in a kinematically complete experiment. Therefore, a dedicated reaction microscope was connected to the beamline of the NEPOMUC positronmsource located at the research reactor FRMII in Garching. Using a reaction microscope the momenta of all particles in the final state can be detected. In order to guide the positrons from the high magnetic field of the beamline into the lower field of the reaction microscope with a minimal loss on intensity, solenoidal coils producing an adiabatic field change have been installed at the transition region. A sophisticated method for the data analysis was developed to reconstruct the time origin of the ionisation process also for the case of a continuous beam. Finally, we were able to identify triple coincident events originating from the fragmentation. The three-dimensional momentum vectors of the three particles in the final state could be obtained for these events. The gained cross sections show that the projectile charge which is inverse compared to electron collisions causes a high mnission of the ionised electron with the projectile in forward direction.