ESR studies of atoms trapped in superfluid helium. I. Technique. ESR spectra of nitrogen atoms

A low-temperature attachment to a standard ESR spectrometer for the investigation of atoms and radicals trapped in superfluid helium is described. The ESR spectra of nitrogen atoms in He II are obtained for the first time. An analysis of the spectra indicates that under the conditions for accumulation of nitrogen atoms in this work the trapped concentrations are low: (N)/sub t//N/sub 2/> or approx. =0.13%. These concentrations are still obtained when the temperature is increased to 4.2 /sup 0/K. Annealing of the sample at T> or =8 /sup 0/K leads to reduction of its atom content.