Ab initio Investigation of Helium Bubble Formation from Trapped He+ Ions in Solid Hydrogen

R. H. Scheicher(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

We are examining the possibility of Helium bubble formation for trapped He+ ions in solid hydrogen. Our procedure is based on an extension of the first-principle cluster approach that we have been using for study of individual He+ ions in solid hydrogen [1]. The present analysis involves a cluster study of two He+ ions in neighboring interstitial positions including all the nearest hydrogen molecule neighbors of both of them, particularly those that are common to both He+ ions. The two neighboring interstitial sites chosen in our work are the adjacent tetrahedral and octahedral sites shown in Fig.1. We are examining if the hydrogen molecules common to the two He+ ions lead to an attractive force between them that can overcome their inherent repulsion. This feature would be expected to manifest itself through an increase in the binding energy for the two adjacent trapped He+ ions as compared to two isolated trapped He+ Such a result would provide support for the possibility of aggregation of He+ ions in solid hydrogen leading to bubble formation.

[1] Abstract entitled "Theory for Relative Strengths of Trapping of He+ Ions in Solid, Liquid and Gaseous Hydrogen" at this
Conference by R. H. Scheicher et al.

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