A new technique to determine gamma emission probability above the neutron threshold without gamma-ray detectors

¹ Center for Nuclear Study, the University of Tokyo, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
² Department of Physics, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
³ RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
⁴ RCNP, Osaka University, 10-1 Mihogaoka, Ibaraki, Osaka, 567-0047, Japan
⁵ Center for Extotic Nuclear Studies, Institute of Basic Science, 55 Expo-ro, Doryong-dong, Yuseonggu, Daejeon 34126, Korea
⁶ Department of Physics, Kyushu University, 744, motooka, nishi-ku, Fukuoka-city 819-0395, Japan
⁷ RIKEN Center for advanced photonics, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
⁸ IGSES, Kyushu University 6-1, Kasugakoen, Kasuga City, Fukuoka 816-8580, Japan
⁹ J-PARC Center, 2-4 Shirakata, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
¹⁰ GSI, Plancksträse 1, 64291 Darmstadt, Germany
¹¹ Department of Physics, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro 152-8550 Tokyo, Japan
¹² KEK Wako Nuclear Science Center, Hirosawa 2-1, Wako 351-0198, Saitama Japan
¹³ Department of Physics, Saitama University, Shimo-Okubo 255, Sakura-ku, Saitama, 339-8670, Saitama, Japan

Published online: 25 June 2025

Abstract

We have developed a new experimental technique to determine the gamma emission probability from unbound states populated by the (d, p) reaction at 20 MeV/nucleon under the inverse kinematics. This was achieved using the decelerating and focusing device OEDO at RIBF. Due to the inverse kinematics, the outgoing reaction residues can be identified by a magnetic spectrometer. By combining the missing spectroscopy with the identification of the residual ions, the γ emission channel was determined event-by-event as a function of the excitation energy, without detecting γ ray from the unbound states. As the first application, the method was used to study the neutron capture reaction on ⁷⁹Se via the (d, p) reaction as a surrogate reaction for the neutron energies up to 5 MeV. Additionally, the technique was employed to investigate the compound reaction channel of (n, γ) cross sections on ¹³⁰Sn.