Increase in the positronium emission yield from polycrystalline tungsten surfaces by sodium coating

• Published in: Surface science 2015-11, Vol.641 (C), p.68-71
• Main Authors: Terabe, Hiroki, Iida, Shimpei, Yamashita, Takashi, Tachibana, Takayuki, Barbiellini, Bernardo, Wada, Ken, Mochizuki, Izumi, Yagishita, Akira, Hyodo, Toshio, Nagashima, Yasuyuki
• Format: Article
• Language: English
• Subjects: Coating; Electron density; Emission; Positron; Positronium; Positrons; Sodium; Sodium coated tungsten; Spectral emittance; Time-of-flight; Tungsten
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2015.05.012

The study of positronium emission from metal surfaces bombarded by slow positrons provides information on the topmost layer of the metals such as electron and positron energy levels because positronium atoms are formed as the result of the interactions between the positrons and the electrons there. In the present work, time-of-flight spectra of ortho-positronium atoms emitted from polycrystalline tungsten surfaces with and without a sodium coating have been measured. The data shows a significant increase on coating in the yield of the 5eV component due to positronium formed from thermalized positrons and conduction electrons. An attempt is made to explain the increase by an emission model based on the formation of positronium in a low electron density surface layer extended by the coating. [Display omitted] •Positronium emission from sodium coated polycrystalline tungsten surfaces is studied.•Time-of-flight spectra for the positronium have been measured.•A significant increase on the coating in the yield of 5eV component was observed.•A model of positronium formation in a low electron density surface layer is proposed.