Re-Os Cosmo chronometer

^<187>Re-^<187>Os对是宇宙计时器中的一种，因为^<187>Re只由r过程产生，其半衰期很长（42.3±1.3Gyr）。另外<187><186>，由于^Os在10 keV的激发态存在一个问题，<187>即在恒星温度下，^<187>Os会被（n，γ）过程耗尽。为了校正损失率，我们用一种新的实验方法测量了^ Os，^ Os和^ Os的（n，γ）截面和中子非弹性截面<186><187><189>。用脉冲中子轰击富集的^<186>Os、^<187>Os和^<189>Os和^<197>Au样品。利用反康普顿NaI（Tl）谱仪，通过探测从Os的中子俘获态到低激发态的瞬发γ射线，测量了Os同位素的（n，γ）截面。为了测量^<189>Os（n，n '）^<189>Os反应截面，我们研制了一种新的探测系统，使用了四个直径为50 mm、厚度为10 mm的锂玻璃探测器，用飞行时间法测量了由^ Os弹性和非弹性散射的中子能量<189>。根据<189>γ射线和γ射线的脉冲高度，可以区分γ射线散射的神经元和γ射线背景。为了准确地获得^ Os的非弹性散射截面<189>，必须防止^7Li（p，n）^7Be反应产生的中子直接进入锂玻璃探测器。为了找到这些屏蔽材料的硼化聚乙烯，镉和硼的适当的安排，已进行了广泛的计算，使用蒙特卡罗代码。此外，经过多次的研究与开发工作，我们终于成功地建立了一套高灵敏度的原子核非弹性散射截面测量系统。我们成功地测量了^<187>Os（n，n '）^<187>Os截面，并获得了高精度的测量结果。

^<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.