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Positronium-surface interaction in the pores of the Vycor glass

1977; IOP Publishing; Volume: 11; Issue: 1 Linguagem: Inglês

10.1088/0022-3719/11/1/020

1747-3802

S M Kim, W. J. L. Buyers,

Atomic and Molecular Physics

The positronium-surface interaction has been studied experimentally and theoretically. The angular correlation of photons from annihilation of positronium on the internal surfaces of porous Vycor glasses has been measured as a function of pore size in the range 2.2-14.0 nm. When the pores were filled with oxygen the angular distribution showed an intense narrow peak, arising from parapositronium annihilation in the pores, superimposed upon a broad distribution. The width of the narrow peak was approximately independent of pore diameter suggesting localisation of the positronium in a surface state. The possible states of positronium in a spherical cavity have been studied theoretically as a function of the strength of the surface potential. The positronium-glass interaction that best fits the data was found to be attractive and strong enough to localise the positronium atom near the surface of the pores. The theory gives a good description of the data with strongly attractive surface well, e.g. approximately 1 eV deep and 0.4 nm wide. The likely origin of the attraction is the strong van der Waals interaction of the highly polarisable positronium atoms.