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Re-Os Cosmo chronometer

Re-Os Cosmo 天文台表

基本信息

批准号：
14204025
负责人：
NAGAI Yasuki
金额：
$ 28.79万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14204025/
关键词：
Cosmo chronology Nuclear Cosmo Clock rapid process slow process nucleosynthesis neutron capture reaction Re-Os pair 中性子捕獲反応弾性散乱非弾性散乱宇宙年令 γプロセス Sプロセス

项目摘要

^<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.

由于187&gT；Re的半衰期很长(42.3±1.3 Gyr)，所以被称为宇宙计时器之一。^&lt；187&gt；OS由S生产。此外，还存在一个问题，它源于10keV的激发态，它可以在恒星温度下被填充，因此^&lt；187&gt；Os通过态的(n，γ)过程被耗尽。为了修正损失率，我们用一种新的实验方法测量了^&lt；186&gt；Os、^&lt；187&gt；Os和^&lt；189；Os的(n，γ)截面和中子非弹性截面。脉冲中子轰击浓缩样品^&lt；186&gt；Os，^&lt；187&gt；Os和^&lt；189&gt；Os和^&lt；197&gt；Au。利用反康普顿NaI(Tl)能谱仪，通过探测从Os的中子俘获态向低能级提供的瞬发伽马射线，测量了Os同位素的(n，γ)截面。为了测量^&lt；189&gt；Os(n，n‘)^&lt；189&gt；Os反应截面，我们用四个直径50 mm、厚度10 mm的锂玻璃探测器研制了一套新的探测系统。用TOF方法测定了~&lt；189&gt；Os弹性和/或非弹性散射的中子能量。根据散射神经元的脉冲高度，可以区分散射神经元和伽玛本底。为了准确地获得^&lt；189&gt；Os的非弹性散射截面，防止^7Li(p，n)^7Be反应直接进入锂玻璃探测器是至关重要的。为了找出这些含硼聚乙烯、镉和硼的屏蔽材料的合理排列，用蒙特卡罗程序进行了大量的计算。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&gt；Os(n，n‘)^&lt；187&gt；Os的截面，测量精度很高。