Generation of He clusters via neutron-He absorption reaction toward visualization of full velocity field in quantum turbulence

松下 琢*; Sonnenschein, V.*; Guo, W.*; 林田 洋寿*; 廣井 孝介  ; 広田 克也*; 井口 哲夫*; 伊藤 大介*; 北口 雅暁*; 鬼柳 善明*; 國立 將真*; 久保 渉*; 齊藤 泰司*; 清水 裕彦*; 篠原 武尚   ; 鈴木 颯*; 富田 英生*; 辻 義之*; 和田 信雄*

Matsushita, Taku*; Sonnenschein, V.*; Guo, W.*; Hayashida, Hirotoshi*; Hiroi, Kosuke; Hirota, Katsuya*; Iguchi, Tetsuo*; Ito, Daisuke*; Kitaguchi, Masaaki*; Kiyanagi, Yoshiaki*; Kokuryu, Shoma*; Kubo, Wataru*; Saito, Yasushi*; Shimizu, Hirohiko*; Shinohara, Takenao; Suzuki, So*; Tomita, Hideki*; Tsuji, Yoshiyuki*; Wada, Nobuo*

For flow visualization study of quantum turbulence in superfluid He, He excimers are unique tracers which follow only normal-fluid component flow above 1 K. To generate detectable small He clouds (clusters) required for full-space velocity field measurements, we have adopted a new method based on neutron absorption reaction of He impurities in He and conducted proof-of-principle experiments. Generation of the He excimers was detected by laser-induced fluorescence using photomultiplier tubes. The fluorescence was observed to increase proportionally to the neutron flux, suggesting that a sufficient amount of He excimers were generated by neutrons. We also estimated the number of He excimers possibly generated by -rays and found that the relevant contribution was less than 40%. Thus, the majority of the He excimers was confirmed to be generated via n-He absorption reactions.