Theoretical study of the pressure effect on the electron-capture beta decay of Be-7 in (BeO)-Be-7 and Be-7(OH)(2)

Ab initio quantum mechanical methods based on the Hartree-Fock approach are used to study the probability of electron capture by the Be-7 nucleus in the (BeO)-Be-7 crystal and the beta phase of the Be-7(OH)(2) crystal modeled as clusters subjected to external pressure. Calculated rates of the increase of the Be-7 nuclear decay constant lambda with pressure in these compounds are substantially smaller than the values found experimentally. We discuss possible reasons for discrepancy between the theory and the experiment. In particular, we demonstrate that the increase of lambda in (BeO)-Be-7 can be accounted for by the discussed phase transformation from the wurtzite to the rock-salt structure.