Sonnenschein V, Tsuji Y, Kokuryu S, Kubo W, Suzuki S, Tomita H, Kiyanagi Y, Iguchi T, Matsushita T, Wada N, Kitaguchi M, Shimizu H M, Hirota K, Shinohara T, Hiroi K, Hayashida H, Guo W, Ito D, Saito Y
Department of Energy Engineering, Nagoya University, Nagoya, Aichi 464-8603, Japan.
Department of Physics, Nagoya University, Nagoya, Aichi 464-8602, Japan.
Rev Sci Instrum. 2020 Mar 1;91(3):033318. doi: 10.1063/1.5130919.
For the purpose of future visualization of the flow field in superfluid helium-4, clusters of the triplet state excimer He are generated along the micro-scale recoil tracks of the neutron-absorption reaction n + He → T + p. This reaction is induced by neutron irradiation of the He fraction contained in natural isotopic abundance liquid helium with neutron beams either from the Japan Proton Accelerator Research Complex, Materials and Life Science Experimental Facility (JPARC)/Materials and Life Science Experimental Facility or from the Kyoto University Institute for Integrated Radiation and Nuclear Science. These He clusters are expected to be ideal tracers of the normal-fluid component in superfluid helium with several advantageous properties. Evidence of the excimer generation is inferred by detection of laser induced fluorescence emitted from the He clusters excited by a purpose-built short pulse gain-switched titanium:sapphire (Ti:sa) laser operating at a wavelength of 905 nm. The setup and performance characteristics of the laser system including the Ti:sa and two continuous wave re-pumping lasers are described. Detection at the fluorescence wavelength of 640 nm is performed by using optical bandpass filtered photomultiplier tubes (PMT). Electrical noise in the PMT acquisition traces could successfully be suppressed by post-processing with a simple algorithm. Despite other laser-related backgrounds, the excimer was clearly identified by its fluorescence decay characteristics. Production of the excimer was found to be proportional to the neutron flux, adjusted via insertion of different collimators into the neutron beam. These observations suggest that the apparatus we constructed does function in the expected manner and, therefore, has the potential for groundbreaking turbulence research with superfluid helium.
为了未来可视化超流氦 - 4中的流场，沿着中子吸收反应n + He → T + p的微观反冲轨迹生成了三重态准分子He的团簇。该反应是通过用来自日本质子加速器研究中心材料与生命科学实验设施（JPARC/MLF）或京都大学综合辐射与核科学研究所的中子束照射天然同位素丰度液氦中所含的He部分来诱发的。这些He团簇有望成为超流氦中正常流体成分的理想示踪剂，具有若干有利特性。通过检测由专门设计的工作波长为905 nm的短脉冲增益开关钛宝石（Ti:sa）激光激发的He团簇发出的激光诱导荧光，推断出准分子生成的证据。描述了包括Ti:sa和两台连续波再泵浦激光器在内的激光系统的设置和性能特征。使用光学带通滤波光电倍增管（PMT）在640 nm荧光波长处进行检测。通过用一种简单算法进行后处理，可以成功抑制PMT采集轨迹中的电噪声。尽管存在其他与激光相关的背景，但通过其荧光衰减特性仍能清晰地识别出准分子。发现准分子的产生与通过在中子束中插入不同准直器来调节的中子通量成正比。这些观察结果表明，我们构建的装置确实按预期方式运行，因此具有开展超流氦开创性湍流研究的潜力。
