中子深度剖面技术研究

Neutron Depth Profiling (NDP) is a nondestructive near-surface mesearment technique，which is mainly used to determine the concentration and distribution of light nuclides, such as He-3, Li-6, Be-7, B-10, etc, in near-surface layer of materials. It is widely used in the materials in the fields of semiconductor, optics, new energy sources and so on. So far, there is no related resreach work in China. Based on an analysis of the advantages and disadvantages of the traditional Si(Au) detection system and the advanced time of flight (TOF) one, a TOF-based detection system will be adopted in the proposed NDP facility, considering its superior depth-resolution. The NDP facility will be connected with the horizontal neutron beam of China advance research reactor (CARR). The methodologies of TOF-NDP will be studied. A software for converting TOF spectrum to energy spectrum of the emitted particles, and then to depth profiling will be programmed. In the newly designed detection system an array of Si(Au) detectors will be placed around the stopping MCP detector, so that a Si(Au) energy spectrum will be accquired at the same time with the TOF spectrum. The Si(Au) detector array will provide both total concentration determination with high sensitivity (large detection solid angle) and an independent set of depth profile data (although with inferior depth resolution) for cross-check with the high resolution profile data from TOF. The concentration and depth profile of light nuclides are expected to be determined with high depth resolution, at the same time high sensitivity, with this NDP facility.

中子深度剖面(NDP)技术是目前国际上蓬勃发展的一种非破坏近表面分析技术，主要用于测量He-3、Li-6、Be-7、B-10等轻核素/元素在材料近表面的含量和分布。这种分析技术在光学、半导体、新能源等高新技术的材料表征方面具有重要的应用价值。国内尚未开展相关技术的方法研究。本项目比较了目前国际上采用的Si（Au）面垒探测器和飞行时间法（TOF）探测出射带电粒子的优缺点，提出在中国先进研究堆（CARR）中子水平孔道上建立具有国际先进水平的、基于微通道板的飞行时间中子深度剖面分析谱仪系统，并开展NDP方法学和应用基础研究。解决飞行时间谱与出射带电粒子能谱转换等关键问题，编写NDP分析软件，首次实现我国高新技术涉及的半导体、核材料等材料表面难以测定的轻核素的高灵敏、高分辨快速深度分布分析。本系统结合了Si（Au）探测器和飞行时间谱仪（TOF）的优点，使NDP同时达到高深度分辨率和高灵敏度。

在CARR堆上建立了中子深度剖面真空靶室、样品架、换样装置、探测系统，设计了中子准直装置，将中子束流限定为直径为15mm大小，并在该系统上开展了中子深度剖面实验研究，看站了中子深度剖面反演算法的研究，用实验进行了检验。针对现在的中子深度剖面分析技术(NDP)，利用多种蒙特卡罗程序以及现有的设备的情况下，基于概率迭代反演计算方法来计算出元素的浓度深度剖面图。根据CARR堆中的现已有的NDP实验装置，作为蒙特卡罗的NDP基础模拟原型来得到基础能谱图，通过标准样品SRM2137来模拟得到的能谱图。通过MATLAB软件来反演迭代编程来反演出SRM2137的浓度深度变化图，并与原已知的浓度深度图进行归一化对比。通过研究发现，用反演计算方法得出的标准物质SRM2137的深度剖面分布是可行的，而且具有一定的先进性。