分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-26
摘要： Doppler broadening and Coincidence Doppler broadening of annihilation radiation experiments have been performed in three kinds of polyethylene glycol (PEG) membrane formed with different average molecular weight using the tunable monoenergy slow positron probe as a function of implantion energy. The obtained positron annihilation parameters are interpreted from two aspects: surface effect and differences in micro-structure or chemical environment of positron annihilation. The experimental results show that the regulation of densification of PEG molecular packing and distribution uniformity from the near surface layer to bulk region in film forming process can be well realized by changing its molecular weight. Combining a variable monoenergetic slow positron beam and these two positron annihilation spectroscopy methods are powerful tool to study positron annihilation characteristics and for polymeric thin-film fine structure analysis.
分类： 物理学 >> 核物理学 提交时间： 2016-09-02
摘要： Reactor neutrino experiments build large-scale detector systems to trap ghost-like neutrinos. In liquid scintillator, a neutral bound state of a positron and an electron named positronium could be formed. The spin triplet state was called ortho-positronium (o-Ps). In this script, an experiment was designed to measure the lifetime of o-Ps, which turned out to be 3.1 ns. A PSD parameter based on photon emission time distribution (PETD) was constructed to discriminate e+/e−. Finally the application of e+/e− discrimination in JUNO experiment was shown. It helps suppression of 8He/9Li backgrounds and improves the sensitivity by 0.6 in χ2 analysis with assumption of σ=1 ns PMT Transit Time Spread, which will bring smearing effect to PETD.
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