Papers by Keyword: Positronium Molecule

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Authors: S.H.M. Deng, D.B. Cassidy, A.P. Mills
Abstract: A single crystal Al (111) sample cleaned by repeated cycles of ion bombardment and annealing was irradiated by a subnanosecond high density positron beam [1] and the resulting positronium lifetime spectra were measured using single shot positron annihilation lifetime spectroscopy (SSPALS) [2]. We observed the amount of positronium emitted dependence on the incident positron beam density, which indicates the formation of positronium molecules (Ps2) at the Al (111) surface [3]. The Ps2 formation probability appears to be extremely sensitive to surface contamination and further experiments under improved vacuum conditions are planned to clarify this effect.
Authors: D.B. Cassidy, S.H.M. Deng, R.G. Greaves, N. Lopez-Valdez, V. Meligne, H.W.K. Tom, A.P. Mills
Abstract: Recent observations of molecular positronium (Ps2) were based on a correlation between changes in positronium (Ps) lifetime spectra associated with the density of an incident positron beam and the population of a positronium (or positron) surface state. While the evidence for molecule formation is compelling it is nevertheless an indirect observation, and has not provided any information about the properties of Ps2 beyond its likely creation. Here we discuss the prospects for a direct observation via laser spectroscopy of a predicted 1S2P excited molecular state. Such a measurement would provide a direct and unambiguous signal of Ps2 formation and would also allow us to determine some properties of the molecule, namely the lifetime of the excited state and the 1S1S-1S2P energy interval.
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