Re-Os Cosmo chronometer

^<187>Re-^<187>Os对被称为宇宙计时器之一，因为^<187>Re仅由r过程产生，其半衰期相当长（42.3±1.3Gyr）。^<187> o是由^<186> o的s过程产生的。此外，在^<187>Os中，有一个源自10 keV激发态的问题，它可以在恒星温度下填充，因此^<187>Os被（n,γ）过程耗尽。为了校正损失率，我们用一种新开发的实验方法测量了^<186>,^<187>和^<189>的（n,γ）截面和中子非弹性截面。用脉冲中子轰击富集了^<186> o、^<187> o、^<189> o和^<197>Au的样品。利用反康普顿NaI（Tl）光谱仪测量了Os同位素的（n,γ）横截面，探测了从Os的中子俘获态向低洼态馈送的提示射线。为了测量^<189>Os(n,n')^<189>Os反应截面，我们开发了一种新的检测系统，该系统使用四个直径为50 mm，厚度为10 mm的锂玻璃探测器。采用TOF方法测定了^<189>Os弹性和/或非弹性散射的中子能量。通过脉冲高度可以区分^<189>Os散射神经元和伽马射线背景。为了准确获得^<189>Os的非弹性散射截面，防止^7Li(p,n) ^7Be反应产生的直接中子进入li -玻璃探测器至关重要。为了找到硼化聚乙烯、镉和硼的屏蔽材料的合理排列，使用蒙特卡罗程序进行了广泛的计算。此外，通过大量的研发工作，我们最终成功地构建了一个高灵敏度的核非弹性散射截面测量系统。我们成功地高精度地测量了^<187> o (n,n')^<187> o的截面。

^<187>Re-^<187>Os pair is known as one of cosmochronometers, since ^<187>Re is produced by only r-process and its half life is quite long 42.3±1.3Gyr. ^<187>Os is produced by s-process of ^<186>Os. In addition, there is a problem originating from the excited state at 10 keV in ^<187>Os, which could be populated at stellar temperature, and therefore ^<187>Os is depleted by the (n,γ)process the through the state. In order to correct for the loss rate we measured both the (n,γ) cross sections and neutron inelastic cross sections of ^<186>Os, ^<187>Os and ^<189>Os using a newly developed experimental method. Pulsed neutrons were bombarded on enriched samples of ^<186>Os, ^<187>Os and ^<189>Os and ^<197>Au. The (n,γ)cross section of Os isotopes was measured using an anti-Compton NaI(Tl) spectrometers by detecting prompt gamma rays feeding from a neutron capture state of Os to low lying states. For the measurement of the ^<189>Os(n,n')^<189>Os reaction cross section we have developed a new detection system with use of four Li-glass detectors with a diameter of 50 mm and a thickness of 10 mm. Neutron energy scattered elastically and/or inelastically by ^<189>Os is determined by employing a TOF method. The discrimination between scattered neuron by ^<189>Os and gamma ray background can be made by their pulse heights. In order to obtain the inelastic scattering cross section of ^<189>Os accurately, it was crucial to prevent direct neutrons from the ^7Li(p,n) ^7Be reaction entering into the Li-glass detector. To find proper arrangement of these shield materials of borated polyethylene, cadmium and Boron, an extensive calculation has been made using a Monte Carlo Code. In addition, through many R & D works we have finally succeeded to construct a high sensitive measuring system of the inelastic scattering cross section of a nucleus. We succeeded to measure the ^<187>Os(n,n')^<187>Os cross section with high accuracy.