title: Swelling of positronium confined in a small cavity.
abstract: The electron density at the positron (contact density) in the ground state positronium (Ps) formed in condensed matter is generally found to be lower than in vacuum. This is usually attributed to microscopic electric fields which polarize Ps, by acting on the two particles of the atom. In this paper we quantitatively investigate an opposite effect. It is due to the confinement of Ps in small cavities existing in the host solid (e.g. free volume in polymers), which increases the contact density. Although this phenomenon is greater, the smaller is the size of the cavity, Ps polarization seems to play anyway a predominant role.
authors.affiliation: Department of Aerospace Science and Technology, Politecnico di Milano, Milano, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Consolati
authors.affiliation: Department of Aerospace Science and Technology, Politecnico di Milano, Milano, Italy.
authors.forename: Fiorenza
authors.initials: F
authors.lastname: Quasso
authors.affiliation: Department of Physics, Università degli Studi di Milano, Milano, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Trezzi
mesh_terms: D000465:Algorithms; D004583:Electrons; D008956:Models, Chemical; D011108:Polymers / Q000737:chemistry*; D011789:Quantum Theory; D014618:Vacuum
chemical_list: D011108:Polymers