Numerical Solution of a Two-Particle Model of Positronium Confined in Small Cavities
G. Tanzi Marlotti a, F. Castellia,b and G. Consolatic,b
aDepartment of Physics, Università degli Studi di Milano, via Celoria 16 I-20133 Milano, Italy
bINFN, sezione di Milano, via Celoria 16 I-20133 Milano, Italy
cDepartment of Aerospace Science and Technology, Politecnico di Milano, via LaMasa 34, I-20156 Milano, Italy
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The positronium atom (Ps) is widely used as a probe to characterize nanoporous and mesoporous materials. Existing theoretical models for describing Ps annihilation rates by pick-off processes generally treat Ps as a point particle confined in a potential well. Hence these models do not justify any change in the internal structure of Ps, which is experimentally accessible by means of the contact density parameter. Recently we formulated a two-particle model in which only the electron is confined in the cavity, while the positron is moving freely and feels the medium via a positive work function. We present here a numerical treatment of the problem of calculating contact densities and pick-off annihilation rates, by using a variational method. Results are in agreement with experimental data for a large class of materials, and suggest a way to connect these data with pore sizes and positron work functions.

DOI: 10.12693/APhysPolA.132.1575
PACS numbers: 36.10.Dr, 34.80.Lx, 78.70.Bj