高效率数字二维多普勒展宽谱仪开发及其在合金析出物中的应用

Positron two-dimensional Doppler broadening(2-DB) technique is a powerful probe to study the microstructure of solid materials. Improving the performance of 2-DB technique, especially for 2-DB with higher count rate and higher energy resolution, will make it possible to detect the microstructure of materials in real-time, and more accurately to investigate the precipitates in alloys. Digital 2-DB spectrometer can simplify the modules of system, reduce the noise caused by electronics, well deal with the pulses coming from detectors, analyze signals online as well as offline, keep lower total price and so on, therefore, the digital apparatus attract lots of interests in positron research society. However, it is not easy to develop digital 2-DB with high count rate, excellent energy resolution and better stability synchronously.. This project, which bases on our earlier work, will use a fast digitizer which includes a Field Programmable Gate Array(FPGA) through coincidence triggering to sample and transfer the signal, and use the signal filtering method to lower the noise and filter the digital pulse signal, and ultimately realize the high efficiency digital 2-DB technique. We will then use the digital 2-DB spectroscopy to characterize and identify the microstructure of the precipitates in alloys. By combining other characterization techniques to correctly identify the microstructure of precipitates in alloys, and explore the origin of nucleating, growing and evolution of precipitates phases in alloys in the course of thermal aging and plastic deformation.

正电子二维多普勒展宽谱技术是研究材料微结构的有力手段，提升二维多普勒展宽谱技术的性能，特别是提高其探测效率和能量分辨率后，将有助于实现对材料微结构的跟踪测量，更准确地研究其结构成分。数字二维多普勒展宽谱仪因能够简化仪器结构、降低电学噪声、灵活处理数字化信号脉冲、能进行离线和在线分析、具有成本优势等优点近来在国内外一些正电子小组发展起来，但未能同时实现谱仪的高计数率、高能量分辨率和稳定性。. 本项目提出利用带现场可编程门阵列（FPGA）的高速数字转换器通过软件符合触发对探测器信号进行高速采样、传输，并采用数字滤波方法对信号进行降噪滤波，实现高效率数字二维多普勒展宽谱技术。发展出的数字二维多普勒展宽谱仪将应用于铝合金材料的析出相研究，并与其它常规材料表征手段相结合，期望能够确定具有争议的析出相结构成分，并探索析出相在时效过程、塑性形变过程中成核、生长及演化机制。

正电子二维多普勒展宽谱技术是研究材料微结构的有力手段，提升二维多普勒展宽谱技术的性能，特别是提高其探测效率和能量分辨率后，将有助于实现对材料微结构的跟踪测量，更准确地研究其结构成分。数字二维多普勒展宽谱仪因能够简化仪器结构、降低电学噪声、灵活处理数字化信号脉冲、能进行离线和在线分析、具有成本优势等优点受到国内外一些科研工作者关注。本项目通过仿真模拟研究光电探测器仪器参数和样品对数字符合多普勒展宽谱仪器性能的影响，得到探头分辨函数的改变将会影响低动量谱的峰高度，但不会导致峰位偏移；探头分辨函数影响高动量谱结果；符合多普勒展宽谱的商谱与样品核芯电子湮没比率、核芯电子高斯分布半高宽和价电子抛物线分布的截止宽度相关；然后，我们利用高速数字数字采集卡组装了一套数字多普勒展宽谱仪，编写了一套完整的数字符合多普勒展宽谱应用软件，具有在线或离线收集和分析数字符合多普勒展宽谱数据能力，并应用数字多普勒展宽谱仪进行了对实验样品的简单测试，具有稳定性和可靠性。在此基础上，我们在继续加强改进数字符合多普勒展宽谱仪硬件和软件，并维护其运行稳定性，达到高计数率、高能量分辨率和高稳定性的目标