A Scaling for Differential Single and Multiple Ionization of Kr by Electron Impact

Differential measurements of Kr ionization by electron impact were performed for an electron beam of 240 eV and 500 eV energies, colliding with a Kr gas jet target. Results for absolute doubly differential cross sections (DDCS) of Kr$^{+}$, Kr$^{2+}$ and Kr$^{3+}$ ionization states are presented. Kr ions are pulled out of the interaction region by means of a pulsed field and recorded by means of a channeltron detector used in coincidence with a projectile detector in order to acquire differential information. DDCS plotted as a function of projectile energy loss and momentum transfer were investigated, some similarities were observed but in general no ``universal curves'' were found. By using a ``reduced momentum'' the DDCS for different angles, energy losses and even for different projectile energies could be compressed into two curves, corresponding to large ($90^\circ \ge \theta \ge 30^{\circ})$ and small ($\theta <30^{\circ})$ scattering angles. These different scalings and variables will be presented and discussed.