The Interference between the Resonance Reaction and the Direct Reaction in the keV-Neutron Capture by ^<18>O and Nucleosynthesis

• Project/Area Number: 13440072
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 素粒子・核・宇宙線
• Research Institution: TOKYO INSTITUTE OF TECHNOLOGY
• Principal Investigator: OHSAKI Toshiro Tokyo Institute of Technology, Research Laboratory for Nuclear Reactors, Research Associate, 原子炉工学研究所, 助手 (80262327)
• Co-Investigator(Kenkyū-buntansha): SHIMA Tatsushi Osaka University, Research Center for Nuclear Physics, Research Associate, 核物理研究センター, 助手 (10222035) ; NAGAI Yasuki Osaka University, Research Center for Nuclear Physics, Professor, 核物理研究センター, 教授 (80028240) ; IGASIRA Masayuki Tokyo Institute of Technology, Research Laboratory for Nuclear Reactors, Associate Professor, 原子炉工学研究所, 助教授 (10114852)
• Project Period (FY): 2001 – 2002
• Project Status: Completed (Fiscal Year 2002)
• Budget Amount: ¥2,200,000 (Direct Cost: ¥2,200,000); Fiscal Year 2002: ¥2,200,000 (Direct Cost: ¥2,200,000)
• Keywords: ^<18>O / Neutron Capture Reaction / Prompt gamma-Ray / s-process / 干渉効果

Research Abstract

The ^<18>O(n,γ)^<19>O reaction cross sections in the keV region are important for studies on the nucleosyntheses in the non-standard inhomogeneous big-bang model and the s process in cool giant stars. Moreover, neutron capture reactions by light nuclei, such as oxygen isotopes are suitable for the measurement of the interference between the resonance reaction and the direct reaction, because these level densities are low.
In this study, neutron capture cross sections of ^<18>O in the 30keV region, which are important for the evaluation of the s-process, were measured. The measurement was carried out by using pulsed neutrons and detecting the prompt rays from the neutron capture reaction. A 136.5 g of 95.1 atom% enriched D_2^<18>O sample was used. Two-dimensional data on neutron time of flight and γ-ray pulse height from the spectrometer were stored into a UNIX workstation in a list mode. As a reference, the measurement of ^<197Au sample was also performed.
As a result, three primary transitions to the second and the first excited states and the ground state of <19>^O were observed for the first time. The strongest one was the transition to the second exited state, whose branching ratio was about 50%. The obtained total capture cross sections were obtained as 8.5±1.7 and 11.9±1.8 μb at 42 and 65 keV, respectively. The present data are consistent with the data by Meissner et al. : 7.93±0.70 μb at kT=25keV.
The obtained result was presented at the international symposium : "Capture Gamma-ray Spectroscopy and Related Topics" held at Prague in 2000.

Research Products

• [Publications] Toshiro Ohsaki et al.: "Measurement of the ^<18>O(n,γ)^<19>O Reaction Cross Sections by Prompt γ-ray Detection Methods at Thermal and keV Energies"Proc.of 11th Int.Symp.on "Capture Gamma-ray Spectroscopy and Related Topics". (in press).
  • Description: 「研究成果報告書概要(和文)」より
• [Publications] T. Ohsaki, M. Igashira, Y. Nagai, K. Kobayashi, T. Kobayashi and Y. Sakurai: "Measurement of the ^<18>O(n, γ)^<19>O Reaction Cross Sections by Prompt γ-ray Detection Methods at Thermal and keV Energies"Proc. Of 11th Int. Symp. On "Capture Gamma-ray Spectroscopy and Related Topics", Prague, Czech. in press. (2002)
  • Description: 「研究成果報告書概要(欧文)」より
• [Publications] Toshiro Ohsaki et al.: "Measurement of the ^<18>O(n,γ)^<19>O Reaction Cross Sections by Prompt γ-ray Detection Methods at Thermal and keV Energies"Proc. of 11th Int. Symp. on "Capture Gamma-ray Spectroscopy and Related Topics". (in press).