天然锂材料含有6Li与7Li两种稳定同位素，两种同位素在能源及国防领域均有着重要的应用前景，目前唯一应用于工业生产的锂同位素分离方法是化学交换法——锂汞齐法。锂汞齐法分离锂同位素时将使用大量的汞，这带来极大的安全风险和生态风险。在此背景下，围绕非汞体系锂同位素分离方法的研究一直在进行。光化学锂同位素分离是一种有一定发展前景的非汞体系锂同位素分离方法，本实验室围绕该方法进行了一系列实验研究，并建成了较为完善的光化学锂同位素分离装置。在这个装置上虽然采用吸收光谱方法实现了锂蒸汽密度及其同位素组成测量，但是测量结果只有经过对吸收信号的进一步处理之后才能得到。为了进一步提高锂同位素光化学法分离实验研究的效率，锂蒸汽的原子密度及其同位素丰度的实时监测是非常必要的。这种实时测量可以动态显示实验参数变化对分离过程的影响，为揭示光化学法锂同位素分离过程的规律提供可能。文中首先介绍了吸收光谱法测量锂蒸汽同位素丰度及密度的基本原理。考虑到分离实验中对两个参量的测量是在弱吸收条件下完成的，设计了弱吸收条件下的吸收信号记录方法，给出了锂同位素密度及丰度与测量量之间关系的数学模型。在介绍了实现数据实时采集和处理的技术基础——虚拟仪器技术后，确定了实验中实时监测锂蒸汽密度和丰度的技术方案，并在此基础上完成了数据采集硬件以及数据处理程序开发环境的选择。数据采集硬件选用了NI公司的USB-6212型数据采集卡，该硬件可以通过USB接口与电脑连接，采集到的数据的存储及实时处理可以通过LabVIEW编程实现。后续处理在对实验过程中的光吸收信号进行采集后发现，信号中存在较大的随机干扰，这对原子密度和同位素丰度的计算造成了很大影响。因此在数据处理程序中增加了平均降噪、快速傅里叶变换（FFT）、反离散傅里叶变换（IDFT）等处理手段，实现了分离实验条件下的锂蒸汽密度和同位素丰度的实时测量。本工作建立的数据实时采集与分析系统在光化学锂同位素分离实验研究中得到了实际验证和考验，满足了相关实验工作的要求。该工作的成果具有应用于其他需要实时监测同位素丰度及原子（分子）密度的实验场合的可能。
Natural lithium material contains two kinds of stable isotopes, 6Li and 7Li, both of which have important applications in nuclear power. For the moment, a chemical exchange method, lithium amalgam method is the only commercial method for the production of lithium isotope. However, we have to be faced with the great security and ecological risk because of the use of mercury in this method. Therefore, a lot of studies on non-Hg lithium isotope separation methods have been conducted.Photo-chemical lithium isotope separation has great research value in the industrial-scale separation of lithium isotope. The experiment set-up has been established for the photo-chemical lithium isotope separation in our lab after a series of experiments. In the set-up the atomic density and isotope ratio of the lithium vapor have been measured by the absorption spectrum of lithium. However, the measurement results were obtained after deeper processing of the absorption signal. The measurement method reduced the research efficiency of photo-chemical lithium isotope separation. Thus it’s necessary to monitor the two parameters in real-time. The real-time measurement can not only dynamically display the influence of experimental parameters on the separation process, but also make it possible to reveal the laws of separation process. Firstly, the paper describes the fundamental principle to measure the atomic density and isotope ratio of the lithium vapor. Considering the experiment condition of weak absorption, a new data recording method and a new mathematical model are established based on differential circuit. The real-time data acquisition and processing are based on virtual instrument technology. The technical scheme for monitoring the atomic density and isotope ratio of lithium vapor in real-time is determined after the introduction of virtual instrument technology. Then the selection of software development platform and data acquisition hardware is made based on the technical scheme. NI USB-6212 data acquisition card, which can be connected to the computer through the USB, is selected as the data acquisition hardware. Then the storage and real-time processing of collected data can be realized by LabVIEW. When processing the collected data in the experiment, strong and random interference which causes a considerable margin of error exists in signals. Therefore, average filter, fast Fourier transform (FFT) and inverse discrete Fourier transform (IDFT) are selected to realize the real-time measurement of the atomic density and isotope ratio of lithium vapor. The real-time data acquisition and analysis system established in the photochemical lithium isotope separation experiment meet the requirements of relevant experiment work after actual verification and test. What’s more, the system can be applied to other experiments in which the real-time measurement of isotopic ratio or atomic density of atoms (molecules) is necessary.
