Theory for relative strengths of trapping of He+ ions in solid, liquid and gaseous hydrogen

R. H. Scheicher, A. N.U. Roy, T. P. Das, K. Ishida, T. Matsuzaki, S. N. Nakamura, N. Kawamura, K. Nagamine

Research output: Contribution to journalArticlepeer-review

Abstract

The study of trapping of He+ ion in solid hydrogen is important both as a problem in solid state physics and also as an applied physics problem in the field of muon catalyzed fusion (μCF). In μCF, He+ ion acts as a trap for μ-, interrupting the chain reaction aspect of the catalytic role of μ- in producing fusion of deuteron and triton and of triton and triton in solid hydrogen composed of 2H-3H and 3H-3H molecules, respectively. Using the Hartree-Fock procedure, combined with procedures for including many-body effects, as well as relaxation effects associated with the He+-H2 distances and the adjustment of the H-H separation, we have investigated the trapping of He+ in gaseous and solid state environments. For the former, the environment of He+ is simulated by a single hydrogen molecule and for the solid by clusters appropriately chosen to represent the hexagonal close-packed structure. Our results for the gaseous state indicate that the trapping is rather strong with a binding energy of 8.5 eV, with almost equal binding energy in the linear and triangular configurations with respect to the H-H direction. For the solid, both the likely sites for He+ trapping, namely the tetrahedral and octahedral interstitial sites, are also found to provide deep traps (8.6 eV) of almost equal strength, independent of the orientations of the neighboring molecules, showing that the trapping is not influenced by the orientational disorder in the surrounding hydrogen molecules. Further, the influence of next nearest neighbor hydrogen molecules is found to enhance the trapping energy for He+ substantially, by 0.6 eV, with the incorporation of the third nearest neighbors having a much smaller added effect, demonstrating the convergence of our results with respect to the size of the cluster chosen to simulate the solid. The substantial influence on the He+ trapping energy found for the neighbors beyond the nearest ones provides an explanation of the greater accumulation of helium in the solid state of hydrogen in μCF experiments as compared to the liquid. Suggestions are made regarding the possible reasons for the almost negligible accumulation of helium in the liquid state.

Original languageEnglish
Pages (from-to)387-395
Number of pages9
JournalHyperfine Interactions
Volume138
Issue number1-4
DOIs
Publication statusPublished - 2001 Dec 1
Externally publishedYes

Keywords

  • Helium accumulation effect
  • Impurities in hydrogen
  • Muon catalyzed fusion

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Nuclear and High Energy Physics
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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