Density dependent resonance behaviour of a perturbed gamma-gamma directional correlation in a magnetic field

Using pure gaseous H275Se sources with densities between 1.9x1015/cm3 and 3.8x1017/cm3, the directional correlation of the 121.1-279.5 keV gamma-gamma cascade of 75As was measured as a function of the strength of an external magnetic field. The anisotropy shows a resonance behaviour around zero magnetic field with a broadening of the curves for increasing density. A comparison with the theory of Leisi was possible for the source with the lowest density. Using the stochastic model of Bosch and Spehl, the theory of Leisi was extended to describe the broadening of the curves. The measured half widths of the curves were fitted to the theory yielding a cross section of 1.6x10-13 cm2 for charge transfer collisions in the eV energy region between As ions and H2Se molecules. (orig.)