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Annihilation characteristics of positrons in free-standing thin metal and polymer films |
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| Authors: | A Uedono K Ito S Ata K Ito X Cao N Oshima R Suzuki M Doyama S Jinno |
| Affiliation: | a Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan b Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan c National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8565, Japan d Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan e Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan f Advanced Nanomaterials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan g Teikyo University of Science and Technology, Uenohara, Yamanashi 409-0193, Japan h Japan Electron Optics Laboratory (JEOL) Ltd., Akishima, Tokyo 196-0021, Japan i Department of Applied Chemistry, Chiba University, Yayoi, Inage, Chiba 263-8522, Japan |
| Abstract: | 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 γ-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. |
| Keywords: | 41 75 Fr 87 50 Gi 78 70 Bj |
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