Flash lamp annealing of tungsten surfaces marks a new way to optimized slow positron yields

16th International Conference on Positron Annihilation

Anwand, W.^1 ; Johnson, J.M.^1,2 ; Butterling, M.^1 ; Wagner, A.^1 ; Skorupa, W.^3 ; Brauer, G.^1

Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf, PF 510119, 01314 Dresden, Germany^1

Department of Physics, University of Texas at Austin, 1 University Station C1600, Austin, TX 78712-0264, United States^2

Institut für Ionenstrahlphysik und Materialforschung, Helmholtz-Zentrum Dresden-Rossendorf, PF 510119, 01314 Dresden, Germany^3

关键词: Annealing procedures;    Flash lamp annealing;    High-efficiency;    Optimum thickness;    Polycrystalline;    Positron diffusion;    Positron sources;    Vacuum condition;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/443/1/012072/pdf
DOI  :  10.1088/1742-6596/443/1/012072

来源: IOP

【 摘 要 】

Tungsten in the form of a mono-crystalline foil with an optimum thickness of about 2 μm is often used as a positron moderator in mono-energetic positron beams with22Na positron sources. The efficiency of such a moderator strongly depends on its prior heat treatment, i.e. an annealing procedure with considerable difficulty at temperatures of about 2000 °C under vacuum conditions. Flash lamp annealing (FLA) has been tested as new method to quickly anneal W foils in order to produce easy manageable, low-cost moderators with a high efficiency. With FLA, just the surface of a W foil is heated above the melting point (3422°C) within 1 to 3 ms, i.e. without melting the whole foil volume. In this way, a surface cleaning is reached connected with a considerable increase in the positron diffusion length. Conventional polycrystalline W foils of 9 μm ± 25% thickness, heat treated by FLA, were characterized and tested as positron moderators. First promising tests result in a moderator efficiency of ∼3*10-4and clearly demonstrate that FLA is also applicable to tungsten meshes.