Neutron flux spectrum revealed by Nb-based current-biased kinetic inductance detector with a B conversion layer

Miyajima, Shigeyuki*; Shishido, Hiroaki*; Narukami, Yoshito*; Yoshioka, Naohito*; Fujimaki, Akira*; Hidaka, Mutsuo*; Oikawa, Kenichi   ; Harada, Masahide   ; Oku, Takayuki   ; Arai, Masatoshi*; Ishida, Takekazu*

We successfully derived the time-dependent flux of pulsed neutrons using a superconducting Nb-based current biased kinetic inductance detector (CB-KID) with a B conversion layer at Japan Proton Accelerator Research Complex. Our CB-KID is a meander line made of a 40-nm-thick Nb thin film with 1-m line width, which is covered with a 150-nm-thick B conversion layer. The detector works at a temperature below 4 K. The evaluated detection efficiency of the CB-KID in this experiment is 0.23% at the neutron energy of 25.4 meV. The time-dependent flux spectra of pulsed neutrons thus obtained are in good agreement with the results obtained by the Monte Carlo simulations.