紧凑型锂同位素分析热电离质谱仪研制

Compact thermal ionization mass spectrometer for lithium isotope analysis

锂同位素测量在核燃料循环中具有重要应用,热电离质谱法精密度高,其是常用的测量手段。传统的方法是使用较大尺寸的商用热电离质谱仪对锂同位素进行分析,其磁分析器的偏转半径多为250 mm,仪器体积较大,价格昂贵。本课题研制出一种紧凑型热电离质谱仪(M90),其磁分析器偏转半径只有90 mm,整机体积小,非常适合锂同位素分析。此紧凑型热电离质谱仪采用模块化设计,由真空系统、离子源、离子透镜、隔离阀、磁质量分析器、检测器、数据采集控制和软件系统组成。真空系统由一台机械泵、涡轮分子泵、离子泵和复合真空规组成,离子源室真空度优于5×10^(-6)Pa,分析室真空度优于5×10^(-7)Pa;离子源由带冷阱的离子源腔室、10工位样品转盘和悬浮高压灯丝电源组成,灯丝电流调节范围介于0~6 A之间;离子透镜由加速电压电极、引出电压电极、狭缝电压电极、上下偏转电压电极、左右偏转电压电极及离子透镜电源组成,各电压调节范围介于0~6 kV之间;磁分析器由磁铁、霍尔探头和磁流电源组成闭环控制系统,能满足质量范围介于6~45 amu之间的需要;检测器由3个独立的法拉第杯及其检测电路组成,检测器输出电压最高到10 V,4 s积分的本底噪声小于30μV;数据采集使用24位ADC数据采集卡实现。软件采用C^(#)语言结合MySQL数据库编写,使用RS485通信协议实现与硬件数据的交换控制。整机对天然锂同位素比值的测试内精密度可以达到0.01%~0.03%的水平。

Lithium isotope measurement plays a significant role in the nuclear fuel cycle.Thermal ionization mass spectrometry(TIMS),known for its high precision,is a commonly used analytical method.Traditionally,large-sized commercial thermal ionization mass spectrometers with a magnetic analyzer deflection radius of 250 mm are employed for lithium isotope analysis,which are bulky and expensive.This study has developed a compact thermal ionization mass spectrometer with a magnetic analyzer deflection radius of only 90 mm,which is small in size and highly suitable for lithium isotope analysis.This compact TIMS features a modular design,consisting of a vacuum system,ion source,ion lens,isolation valve,magnetic mass analyzer,detector,data acquisition and control,and software system.The vacuum system is composed of a mechanical pump,a turbomolecular pump,an ion pump,and a compound vacuum gauge,achieving a vacuum level in the ion source chamber better than 5×10^(-8)hPa and in the analysis chamber better than 5×10^(-9)hPa.The ion source consists of an ion source chamber with a cold trap,a 10-position sample turntable,and a floating high-voltage filament power supply with a filament current adjustment range between 0 to 6 A.The ion lens is made up of acceleration voltage electrodes,extraction voltage electrodes,slit voltage electrodes,upper and lower deflection voltage electrodes,left and right deflection voltage electrodes,and an ion lens power supply,with each voltage adjustable between 0 to 6 kV.The magnetic analyzer forms a closedloop control system with a magnet,Hall probe,and magnet power supply,capable of meeting the mass range requirements between 6 to 45 amu.The detector is composed of three independent Faraday cups and their detection circuits,with the detector output voltage reaching up to 10 V and the background noise of a 4-second integration being less than 30μV.Data acquisition is realized using a 24-bit ADC data acquisition card.The software is written in C^(#)language combined with a MySQL database,employing the RS485 communication protocol to facilitate data exchange and control with the hardware.The overall instrument achieves an internal precision level for the measurement of natural lithium isotope ratios ranging from 0.01%to 0.03%.