Hyperfine Interaction Induced by Electron Capture. I.γ−γDirectional-Correlation Experiments

$\gamma -\gamma$ directional -correlation experiments performed on low-density gaseous sources of xenon isotopes are described. The angular correlations corresponding to the cascade transitions of 172-203 keV in ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$ and 55-188 keV in ${}_{}{}^{125}{}_{}{}^{}\mathrm{I}$ have been measured and found to be strongly perturbed. The effect is ascribed to the hyperfine interaction of the iodine ions that are formed following $K$ capture of xenon isotopes. An interference phenomenon that results in the appearance of a resonance in the coincidence counting rate has been observed for the $\gamma -\gamma$ cascade of 172-203 keV. The effect is interpreted as being due to the crossing of hyperfine energy levels at zero magnetic field.