ESR study of atomic hydrogen and tritium in solid T₂and T₂:H₂matrices below 1 K

Abstract

We report on the first ESR study of atomic hydrogen and tritium stabilized in a solid T2 and T2:H2 matrices down to 70 mK. The concentrations of T atoms in pure T2 approached 2 × 10 20 cm −3 and record-high concentrations of H atoms ∼ 1×10 20 cm −3 were reached in T2: H2 solid mixtures where a fraction of T atoms became converted into H due to the isotopic exchange reaction T+H2 →TH+H.The maximum concentrations of unpaired T and H atoms was limited by their recombination which becomes enforced by efficient atomic diffusion due to a presence of a large number of vacancies and phonons generated in the matrices by β-particles. Recombination also appeared in an explosive manner both being stimulated and spontaneously in thick films where sample cooling was insufficient. We suggest that the main mechanism for H and T migration is physical diffusion related to tunneling or hopping to vacant sites in contrast to isotopic chemical reactions which govern diffusion of H and D atoms created in H2 and D2 matrices by other methods.

Electron spin resonance study of atomic hydrogen stabilized in solid neon below 1 K

“…This work follows our previous study of unpaired atoms of hydrogen isotopes in solid films containing tritium [27]. Electrons with average energy of 5.7 keV resulting from tritium β-decay serve as an effective source of atoms due to in situ dissociation of molecules in the matrix.…”

“…The H atoms generated by β-particles in solid H 2 may recombine during thermalization, and the resulting fast recombination might lead to decreasing of their yield. Previously we found out that every β-particle generates about 50 H atoms in a solid H 2 film [27] which is more than an order of magnitude smaller as compared to that observed in the gas-phase [35]. Although the matrix may provide pathways for an excited molecule to relax back to the ground state without being dissociated, it might be considered that a significant number of H atoms in pure H 2 instantaneously recombine back, thus reducing the H atom yield.…”

Electrons Trapped in Solid Neon–Hydrogen Mixtures Below $$1\, \hbox {K}$$

“…The present sample cell was previously used for studies of solid tritium films [17] and, as a result, a certain number of tritium atoms and molecules diffused into the ESR mirrors and the copper walls of the sample cell. These tritium impurities serve as a constant source of 5.7 keV electrons resulting from its β-decay.…”

Evidence for melting of HD and D2 clusters in solid neon below 1 K

“…The QM also provides an opportunity to detect possible superfluidity of deposited films which would decouple from the quartz oscillations and lead to an increase of the QM oscillation frequency. The present sample cell was also used in our previous studies of solid tritium films [16] and, as a result, a number of tritium atoms and molecules remained trapped in the ESR mirrors and the copper walls of the sample cell. The electrons released in β-decay of remaining tritium dissociate a fraction of HD and D 2 molecules in Ne:HD and Ne:D 2 solid samples, respectively, and discernible ESR signals of H and D atoms can be observed after a few hours of sample storage.…”