Construction of a mass spectrometric system for isotope analysis of argon from micro-gram-size samples

在没有VG工程师的情况下安装了新的VG5400。1996年6月20日获得了残留气体的质谱图。之后，对其进行了改进和修改。1996年12月27日开始对地热气体样品进行氦同位素分析。所有岩石样品的惰性气体(He、Ne、Ar、Kr和Xe)都是从1997年1月18日开始测量的，其中大部分是来自地幔的包体。通过对低惰性气体浓度样品的分析，获得了较好的稳定性和空白水平。然而，与我实验室灵敏度最高的MS-II质谱仪相比，其灵敏度并不令人满意。原因可能是由于离子源中灯丝的对准不足。1)质谱仪真空：-lt；5x10^；-10&gt；Torr绝对灵敏度：5x10^&lt；-4&gt；A/Torr(用于Ar)检测下限：5x10^&lt；-15&gt；cm^3STP(用于Ar)同位素比率分析精度：1%(对于^lt；40&gt；Ar/^&lt；36&gt；Ar与5x10^；-10&gcm^；40&gt；ar)空白：5x10^&lt；-12&gt；Cm^3STP(用于^lt；40；gt；ar)2)稀有气体提取净化系统真空：&lt；5x10^；-10&gt；塔式加热器毛坯：&lt；3x10^；-9&gt；cm^3STP(用于^lt；40&gt；ar)激光提取毛坯：&lt；10^lt；-11&gt；cm^3STP(用于^lt；40&gt；ar)3)惰性气体可测量绝对体积的系统总动态范围：10^lt；-7；-10^lt；-16不同稀有气体提取方法的可行性：钽炉：镁-克样品大小激光提取：镁-杯(-ng)粉碎和熔化

A new VG5400 was installed without VG engineer. Residual gas mass spectrum was obtained on June 20,1996. After that, it was improved and modified. Helium isotopic analyzes of geothermal gas samples began on December 27,1996. All noble gases (He, Ne, Ar, Kr and Xe) of rock samples, mostly mantle derived xenoliths, were measured from January 18,1997. Fairly good stability and blank level have been attained through the analyzes of samples with low noble gas concentrations. However, sensitivity is not satisfactory if it is compared with that of the mass spectrometer, MS-II,with the highest sensitivity in my laboratory. The reason is probably due to an insufficient alignment of filament in the ion source. It will be improved in the near future.Summary of performed specifications1) Mass spectrometerVacuum : <5x10^<-10>TorrAbsolute sensitivity : 5x10^<-4>A/Torr (for Ar)Detection limit : 5x10^<-15>cm^3STP (for Ar)Precision of isotope ratio analysis : 1% (for ^<40>Ar/^<36>Ar with 5x10^<-10>cm^3STP^<40>Ar)Blank : 5x10^<-12>cm^3STP (for ^<40>Ar)2) Noble gas extraction and purification systemVacuum : <5x10^<-10>TorrBlank of Ta-heater : <3x10^<-9>cm^3STP (for ^<40>Ar)Blank of laser extraction : <10^<-11>cm^3STP (for ^<40>Ar)3) Total systemDynamic range of measurable absolute volume of noble gases : 10^<-7>-10^<-16>cm^3STPAvailability of different methods of noble gas extraction : Ta-furnace : mg-g sample size Laser extraction : mg-mug (-ng) Crush and melt