Ultra High Sensitive Neutron Dosimetry by detection of trace elements produced through nuclear reactions in Reactor Structural Materials with Resonance lonization Spectroscopy

本研究旨在发展共振电离光谱（RIS）的超高灵敏度中子剂量测定技术，以替代传统的基于放射性测量的方法。RIS系统与离子质谱仪相结合，用于测量中子核反应产生的微量元素的浓度和/或同位素分布，特别是用于检测ppb级浓度的反应堆结构材料上的稳定和/或长寿命放射性同位素，很少或没有等压干扰的背景。为建立这种新方法，包括中子剂量估计的数据分析，进行了基础实验和理论考虑。主要研究成果总结如下：1。制作了用于气态和固体样品中微量元素检测的RIS系统原型，并通过Xe气体分析明确了系统的基本性能，如检出限等。对中子辐照后SUS元素的有效RIS方案进行了理论研究和实验验证。特别是建立了谐振激光烧蚀的理论模型，可以很好地解释离子产额与入射激光功率和波长关系的实验结果。此外，通过改进质谱仪的离子提取，发现其检测灵敏度远高于传统的放射性测量方法。提出了一种新的基于神经网络的中子剂量估计方法，该方法适用于RIS数据模式分析。通过活化箔数据的中子谱调整实例，发现该方法在计算简单、求解有效等方面比传统方法具有潜在的优势。

The present study is aiming at the development of ultra high sensitive neutron dosimetry technique with Resonance lonization Spectroscopy (RIS) as an alternative for conventional methods based on radioactivity measurement. The RIS system combined with an ion mass spectrometer is applied to the measurement of concentration and/or isotopic distribution of trace elements produced by nuclear reactions with neutrons, in particular for the detection of stable and/or long-lived radioactive isotopes on reactor structural materials at ppb level concentration with little or no background from isobaric interferences. The basic experiments and theoretical consideration have been made to establish this new methodology including the data analysis for neutron dose estimation.The main research results are summarized as follows;1. A prototype RIS system was fabricated for detection of trace elements in gaseous and solid samples, and the basic system performance such as a detection limit was made clear through Xe gas analysis.2. Efficient RIS schemes for SUS elements after neutron irradiation were theoretically investigated and verified through experiments. In particular, a theoretical model was developed on resonant laser ablation, which can well explain the experimental results on the dependence of ion yields on incident laser power and wavelength. In addition, by improving the ion extraction to a mass spectrometer, it was shown that the detection sensitivity could be much higher than that of the conventional radioactivity measurement.3. A new method for neutron dose estimation was developed on the basis of neural network, which would be suitable for RIS data pattern analysis. Through examples of neutron spectrum adjustment from activation foil data, it was found that the present method has potential advantages over the conventional ones in computational simplicity and solution validty.