Measurement of the hyperfine interaction of free⁷⁵As ions In H₂, He, Ne, Kr and Xe buffer environments and estimate of clolision cross sections in the eV and meV energy region

Abstract

With the time-integral perturbed angular correlation (TIPAC) method the pressure dependence of the perturbation of the 121.1–279.5 keV γ-γ cascade in⁷⁵As has been investigated using gaseous H₂ ⁷⁵Se sources in different buffer environments. The obtained attenuation coefficients G₂₂ (∞) in the range of 0.55 to 1.0 were fitted with a theoretical stochastic model. In the region of low density, where the correlation time τ_C is large compared to the lifetime τ of the intermediate level of the nucleus, charge transfer collision cross sections have been evaluated between 8.1·10⁻¹⁶ cm² for He, 1.3·10⁻¹⁴ cm² for Xe and 1.8·10⁻¹⁴ cm² for the molecular H₂ buffer gas. For increasing densities of the buffer gases the correlation time τ_C became small compared to the intermediate lifetime τ. The main effect in this region is the depolarization, and we found cross sections between 5.2·10⁻¹⁵ cm² for He, 8.7·10⁻¹⁴ cm² for Xe and 1.2·10⁻¹³ cm² for the H₂ buffer gas.