Nonresonant -wave direct capture and interference effect observed in the OO reaction
OO反応における非共鳴p波直接捕獲と干渉効果
永井 泰樹*; 木下 充隆*; 井頭 政之*; 延原 由利子*; 牧井 宏之 ; 三島 賢二*; 嶋 達志*; Mengoni, A.*
Nagai, Yasuki*; Kinoshita, Mitsutaka*; Igashira, Masayuki*; Nobuhara, Yuriko*; Makii, Hiroyuki; Mishima, Kenji*; Shima, Tatsushi*; Mengoni, A.*
We measured the total capture cross section of the OO reaction, as well as partial cross sections leading to the ground ( and first excited ( states in O. The measurement was carried out at average neutron energies of 157, 349, 398, 427, 468, 498, and 556 keV by using pulsed neutrons produced via the LiBe reaction and a -ray detection system based on an anti-Compton NaI(Tl) spectrometer. We observed the interference effect between the resonance state at 4554 keV of O, corresponding to a neutron energy of 411 keV in the center-of-mass system, and a non-resonant contribution in the capture process. The measured partial cross sections are in good agreement with theoretical calculations obtained taking into account the interference between the resonance and a non-resonant p-wave direct radiative capture contribution. Using the present results, together with our previous measurement, we derived the Maxwellian-averaged capture cross sections (MACS) for thermal energies between kT = 5 and 100 keV, key quantities for process nucleosynthesis studies in massive stars.