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首页> 外文OA文献 >Mass measurements of 238U-projectile fragments for the first time with a Multiple-Reflection Time-Of-Flight Mass Spectrometer
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Mass measurements of 238U-projectile fragments for the first time with a Multiple-Reflection Time-Of-Flight Mass Spectrometer

机译：多反射飞行时间质谱仪首次对238U弹丸碎片进行质量测量

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摘要

Mass measurements of short-lived uranium projectile fragments were performed for the first time with a Multiple-Reflexion-Time-of-Flight Mass Spectrometer (MR-TOF-MS). A major part of this doctoral work was a novel development of a data analysis method for the MR-TOF-MS mass measurements of exotic nuclei at the fragment separator FRS at GSI. The developed method was successfully applied to the data obtained from two pilot experiments with the MR-TOF-MS at the FRS in 2012 and 2014. A substantial upgrade of the experimental setup of the MR-TOF-MS was also performed in the frame work of this doctoral thesis after the first run.In the experiments projectile fragments were created with 1000 MeV/u 238U ions in a Be/Nb target at the entrance of the in-flight separator FRS. The exotic nuclei were spatially separated, energy bunched and slowed down with the ion-optical system of the FRS combined with monoenergetic and homogeneous degraders. At the final focal plane of the FRS the fragments were completely slowed down and thermalized in a cryogenic stopping cell (CSC) filled with 3-5 mg/cm^2 pure helium gas. The exotic nuclei were fast extracted from the CSC to enable mass measurements of very short-lived fragments with the MR-TOF-MS. The achievement of this goal was successfully demonstrated with the mass measurement of 220Ra ions with a half-life of 17.9 ms and 11 detected events. The mass measurements of the isobars 211Fr, 211Po and 211Rn have clearly demonstrated the scientific potential of the MR-TOF-MS for the investigation of exotic nuclei and the power of the data analysis system. Difficult measurements with overlapping mass distributions with only a few counts in the measured spectra were the challenge for the new data analysis method based on the maximum likelihood method.The drifts during the measurements were corrected with the developed time-resolved calibration method. After the improvements of the setup as a consequence of the experience of the first experiment in 2012 and the applied time-resolved calibration method a mass resolving power of 400,000 has been achieved in the experiment in 2014. The achieved mass accuracy in these pilot experiments were about $mathsf{1cdot 10^{-6}}$. The contribution of the software and the resulting systematic errors were in the 10$^{-8}$ range. The reliability of the present analysis method was carefully checked in detailed simulations with a realistic peak shape approximated by an exponentially modified Gaussian distribution. Both list mode data and measured histograms were treated in the data analysis. The analysis method was tested with strongly overlapping mass distributions and low count rates including a variable amount of back ground. In summary, the experimental setup for mass measurements of very rare and short-lived nuclei and the corresponding data analysis have reached with this work and results of the present thesis a great potential for high-resolution measurements in future experiments. There mass measurements with 10 events can be performed with a residual uncertainty of $mathsf{4.5 cdot 10^{-7}}$ at a mass resolving power of 400,000.
机译：首次使用多反射飞行时间质谱仪（MR-TOF-MS）对短寿命铀弹丸碎片进行了质量测量。这项博士论文的主要部分是数据分析方法的新开发，该方法用于在GSI的碎片分离器FRS上对异质核进行MR-TOF-MS质量测量。所开发的方法已成功应用于2012年和2014年FRS的两次MR-TOF-MS试点实验获得的数据。在框架工作中还对MR-TOF-MS的实验设置进行了重大升级。实验中，在飞行分离器FRS入口处的Be / Nb目标中，用1000 MeV / u 238U离子制造了弹丸碎片。 FRS的离子光学系统结合了单能和均质降解剂，使外来核在空间上分离，能量聚集并减慢了速度。在FRS的最终焦平面上，将碎片完全放慢并在充满3-5 mg / cm ^ 2纯氦气的低温停止单元（CSC）中加热。从CSC中快速提取了外来核，从而可以使用MR-TOF-MS对非常短寿命的碎片进行质量测量。通过对220Ra离子进行质量测量，半衰期为17.9 ms，并检测到11个事件，成功地证明了这一目标的实现。等压线211Fr，211Po和211Rn的质量测量清楚地证明了MR-TOF-MS在研究外来核和数据分析系统功能方面的科学潜力。基于最大似然法的新数据分析方法面临的挑战是，在质谱图中仅具有少量计数的重叠质量分布的困难测量。使用发达的时间分辨校准方法校正测量过程中的漂移。经过2012年第一个实验的经验和应用的时间分辨校准方法对设置进行了改进，2014年的实验中实现了40万的质量分辨能力。大约$ mathsf {1cdot 10 ^ {-6}} $。该软件的贡献和由此产生的系统错误在10 $ ^ {-8} $范围内。在详细的模拟中仔细检查了本分析方法的可靠性，并通过指数修正的高斯分布近似了实际的峰形。在数据分析中处理了列表模式数据和测量的直方图。分析方法在强烈重叠的质量分布和低计数率（包括可变背景量）下进行了测试。综上所述，这项工作已经完成了用于非常稀有和短寿命原子核质量测量的实验装置以及相应的数据分析，并且本论文的结果在未来的实验中具有高分辨率测量的巨大潜力。可以在400,000的质量分辨力下以$ mathsf {4.5 cdot 10 ^ {-7}} $的残留不确定度执行带有10个事件的质量测量。

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    Ebert Jens;

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  • 年度 2016
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