CW ESR studies of impurity-helium condensates containing krypton and hydrogen atoms

Impurity-Helium condensates (IHCs) containing krypton and hydrogen atoms have been studied in superfluid helium-4 via CW ESR techniques. The IHCs studied in this work are gel-like aggregates of nanoclusters composed of krypton and hydrogen atoms. We have found that such samples contain very high average concentrations of hydrogen atoms (∼10¹⁸cm^-3) as obtained by integration of the microwave absorption signal. Local concentrations (∼10¹⁹cm^-3) of H atoms were calculated from the ESR line width. Detailed studies of the ESR line shapes lead to the conclusion that a large fraction of the H atoms lies on the krypton cluster surfaces.