Ion molecule collisions investigated via nuclear resonance fluorescence

The method of nuclear resonance fluorescence has been applied to analyse the profileN(E) of the 285 keV gamma line of⁷⁵As after electron capture decay of⁷⁵Se in gaseous⁷⁵SeH₂ sources. The profileN(E) depends on the velocity distribution of the radioactive As ions at the moment of γ-decay and, hence, is strongly dependent on the slowing down mechanism. Investigating sources with pressures of 1.5, 15, and 177 Torr different states of the slowing down process could be studied. A simple model is developed that describes the basic properties of the experimental line profiles.