R. H. Scheicher(1), A. N. U. Roy(1), T. P. Das(1), K. Ishida(2),
T. Matsuzaki(2), S. N. Nakamura(2), N. Kawamura(2), K. Nagamine(2,3)
(1) Department of Physics, State University of New York at Albany,
Albany, NY 12222, USA
(2) Muon Science Laboratory, RIKEN (The Institute of Physical and
Chemical Research), Wako, Saitama 351-0198, Japan
(3) Meson Science Laboratory, High Energy Accelerator Research Organization,
Oho 1-1, Tsukuba, Ibaraki 305-0801, Japan
The trapping of He+ ion in solid hydrogen has been studied because of
its basic importance both as a solid state problem as well as in the field
of muon catalyzed fusion (µCF) as a trap for µ-
[1], interrupting the chain 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. Using the Hartree-Fock procedure, combined with procedures for
including many-body effects, as well as relaxation effects associated with
the He+-H distances and the adjustment of the H-H separation, the trapping
of He+ in gaseous and solid state environments has been studied.
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
indicates that the trapping is rather strong with a binding energy of 8.5
eV, with almost equal binding energy in the linear and perpendicular 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. Lastly,
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
influence, demonstrating the convergence of our results with respect to
the size of the cluster chosen to simulate the solid. The substantial added
influence of the neighbors beyond the nearest ones provide an explanation
of the greater accumulation of He gas, in the solid state of hydrogen as
compared to the liquid state, in µCF experiments.
[1] K. Nagamine and M. Kamimura, Advances in Nuclear Physics, Vol. 24,
edited by J. W. Negele and E. W. Vogt, Plenum
Press, New York (1998)