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

Using pure gaseous H₂ ⁷⁵Se sources with densities between 1.9×10¹⁵/cm³ and 3.8·10¹⁷/cm³, the directional correlation of the 121.1–279.5 keV gamma-gamma cascade of⁷⁵As 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 1.6 ×10^?13 cm² for charge transfer collisions in the eV energy region between As ions and H₂Se molecules.