Study of the stabilization and recombination of nitrogen atoms in impurity–helium condensates

Abstract

The stabilization and recombination of nitrogen atoms N(4S) in nitrogen-helium and nitrogen–neon-helium condensates obtained by the injection of impurity particles from a gas discharge into bulk superfluid helium are investigated by the EPR method. It is established that the stabilized nitrogen atoms reside inside and on the surface of impurity clusters forming a porous structure in the bulk superfluid helium. The possibility of increasing the specific energy of impurity–helium condensates by increasing their density through mechanical pressing is investigated. For nitrogen-helium condensates an eightfold increase in the specific energy is achieved. The recombination loss of N(4S) upon heating of impurity–helium condensates in the temperature range 1.7–7 K is detected. This permits verification of the mechanism of thermoluminescence of impurity–helium condensates.

On charged impurity structures in liquid helium

“…The thermoluminescence mechanism proposed agrees well with the experimental results of the ESR studies of IHCs containing nitrogen atoms: the number of stabilized N( 4 S) atoms during the warm-up of the samples in bulk He II remains almost constant [8].…”

“…Such particles and systems have found many different applications: visualization of flows and quantum vortices in superfluid helium [2][3][4]; study of energy transfer phenomena in liquid helium [5]; development of new high-energy density materials [6][7][8]; investigation of tunneling reactions of hydrogen isotopes in impurity-helium condensates [9]; structural studies of rare gas, molecular deuterium and nitrogen nanoclusters [10][11][12]; study of cold neutron interaction with watergels [13,14]; synthesis of metallic nanowires in superfluid helium [15,16]. Laser ablation of metallic target in solid helium-4 allows to create so-called icebergs (helium crystals doped with metallic particles) remaining metastable below the melting curve [17,18].…”

Atomic and molecular defects in solid 4He

“…Their electron-spin resonance (ESR) spectra were studied in [246,[238][239][240][241][242][243]247,248]. ESR spectra were observed using a standard ESR spectrometer operating at 9 GHz.…”

Stabilization of H and D atoms in krypton–helium nanocondensates

“…They possess an aerogellike structure formed by krypton hico nanoclusters (mean size of 5.4 nm) covered with a solid helium layer [17,18]. The average densities of as-prepared Kr-He samples were determined by x-ray absorption measurements and were found to be ~10 19 cm -3 , about 0.1% of the bulk Kr density.…”

“…A discussion of some of the work discussed herein has also appeared in other publications [12,13]. Macroscopic samples (volume ~cm 3 ) of IHCs containing the record average concentration of H and D atoms, 1.2·10 19 and 3.3·10 19 per cm 3 , respectively, were created.…”