应用Argus多接收稀有气体质谱仪准确测量空气的Ar同位素组成

稀有气体质谱仪准确测量氩同位素组成是Ar-Ar法高精度定年的前提,目前测量氩同位素主要应用单接收或多接收质谱仪,其中多接收稀有气体质谱仪在数据准确性和重现性等方面具备优势。本文研究了Argus多接收稀有气体质谱仪应用于测量Ar同位素过程中一些主要因素对测量结果准确度和重现性的影响情况。结果表明,整套系统在静态模式下不同时间段的本底值极低,不影响测定;仪器电子倍增器的接收效率优于99.67%,可显著提高Ar低含量样品测量精度,当⁴⁰Ar信号强度低于0.5 V时,用电子倍增器测量⁴⁰Ar/³⁶Ar组成的标准偏差仅为0.11%,而用法拉第杯测量⁴⁰Ar/³⁶Ar组成的标准偏差为0.53%;仪器的质量歧视效应可通过多次循环测量并采用指数定律获得稳定的质量歧视校正因子(此值相对标准偏差为0.0434%),实现对Ar同位素组成的准确校正。本文以测量空气中的氩同位素组成为例,证明了Argus多接收稀有气体质谱仪的测试效率比单个接收器跳峰方式的测试效率高,测试结果更精确,因此适合年轻样品或含钾量极低的样品的Ar-Ar高精度定年工作。

Accurate Measurement of Argon Isotope Composition of Air by Argus Multi-collector Noble Gas Mass Spectrometer

The accurate measurement of Argon isotopes is the primary of Ar-Ar dating with high precision, The two main kinds of instruments for Argon isotopes measurement are single collector and multi-collector mass spectrometers, where the multi-collector noble gas mass spectrometer has advantage on the accuracy and reproducibility of the data. The paper discussed some main factors which affect the accuracy and repoducibility of the results during the measurement of the Argon isotopes by the Argus multi-collector noble gas mass spectrometer. Results show that the background of the whole system in static mode has little effect on the Argon isotopes composition measurement. The efficiency of the multiplier of the instrument is superior to 99.67%, which can measure the small signal precisely. When the signal of ⁴⁰Ar is less than 0.5V, the standard error is only 0.11% of the ⁴⁰Ar/³⁶Ar measured by the CDD, while the standard error is 0.53% when measured by the Faraday Cup. The mass discrimination effect of the instrument is existed but could be calibrated with Logarithmic Law through the repeated measurement of argon isotopes in air, the relative standard error of the mass discrimination is only 0.0434%, indicate that the mass discrimination effect is very stable. The paper take the argon isotopes in air as an example, proved that the efficiency of the measurement by Argus multi-collector mass spectrometer is higher than that of the single-collector method, the data is more precise and accurate.Therefore, it is very suitable for the high precise Ar-Ar dating research of the young samples or poor-potasium samples.