Annihilation characteristics of positrons in free-standing thin metal and polymer films

作者：Uedono A^*; Ito K; Nakamori H; Ata S; Ougizawa T; Ito K; Kobayashi Y; Cao X; Kurihara T; Oshima N; Ohdaira T; Suzuki R; Akahane T; Doyama M; Matsuya K; Jinno S; Fujinami M

来源：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms , 2008, 266(5): 750-754.

DOI：10.1016/j.nimb.2007.12.104

• positronium
• positron
• thin film
• metal
• polymer

Annihilation characteristics of positrons and positronium (Ps) in thin metal and polymer films were studied. Monoenergetic positrons were implanted into free-standing thin W and Au films and the annihilation gamma-rays of positron-electron pairs were measured as a function of the incident energy of positrons. At the front-side surfaces of the films, an emission of Ps into vacuum and a resultant self-annihilation of ortho-Ps (o-Ps) were observed. At the backside surfaces, the Ps emission was found to be enhanced by an increase in the numbers of epithermal positrons and/or secondary electrons introduced by the impact of energetic positrons. For thin polymer films (polyester and polystyrene), the emission rate of o-Ps from the backside surfaces was higher than that from the metal films, which was attributed to the out-diffusion of o-Ps formed in the films. Those results suggested that the emission rate of Ps into vacuum was sensitive to the Ps formation process in the bulk and at the surface.

• 出版日期2008-3