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

keV区^<18>O（n，γ）^<19>O反应截面对于研究非标准非均匀大爆炸模型中的核合成和冷巨星中的s过程具有重要意义。此外，轻核（如氧同位素）的中子俘获反应由于能级密度低，适合于测量共振反应和直接反应之间的干扰，因此，<18>本文测量了对评价s过程非常重要的^ O在30keV区域的中子俘获截面。测量是通过使用脉冲中子和探测来自中子俘获反应的瞬发射线来进行的。使用136.5克95.1原子%富集的D_2^<18>O样品。从谱仪上获得的中子飞行时间和γ射线脉冲高度的二维数据以列表方式存储在UNIX工作站上。作为参考，我们还对&lt;197 Au样品进行了测量，首次观察到了^O的第二、第一激发态和基态的三次跃迁<19>。最强的一个是过渡到第二激发态，其分支比约为50%。在42和65 keV下，获得的总俘获截面分别为8.5±1.7和11.9±1.8 μB。在25keV时，测量值为7.93±0.70 μB，与Meissner等人的测量值一致。所得结果已在2000年于布拉格召开的“俘获γ射线谱学及相关课题”国际研讨会上发表。

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.