High-precision potassium measurements using laser-induced breakdown spectroscopy under high vacuum conditions for in situ K-Ar dating of planetary surfaces
High-precision potassium measurements using laser-induced breakdown spectroscopy under high vacuum conditions for in situ K-Ar dating of planetary surfaces
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在高真空条件下使用激光诱导击穿光谱进行高精度钾测量，用于行星表面的原位 K-Ar 定年
DOI：
10.1016/j.sab.2015.02.002
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
T. Matsui
中科院分区：
文献类型：
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作者：
Y. Cho;S. Sugita;S. Kameda;Y. N. Miura;K. Ishibashi;S. Ohno;S. Kamata;T. Arai;T. Morota;N. Namiki;T. Matsui
为了研制适用于行星探测任务的原位等时K-Ar定年仪器，我们在高真空（10- 6Pa）条件下进行了一系列激光诱导击穿光谱（LIBS）K测量实验。与全岩测量方法不同，等时线测量需要在真空室中进行LIBS实验，因为同时进行Ar同位素测量是必要的。然而，详细检查的检测限和准确性，这种方法在低压下还没有被广泛研究之前。在这项研究中，在高真空条件下的K测量的能力进行了检查，使用LIBS。一个紧凑的Czerny-Turner型光谱仪配备了一个电荷耦合器件（CCD）作为检测器。用LIBS方法测量了23个地质标准样品。使用769.89 nm处的第二强K发射线进行校准，因为766.49 nm处的最强发射线可能受到另一发射线的强干扰。使用在777 nm处的氧线的内部归一化构建K的校准曲线，并通过幂律函数很好地拟合。基于预测带法，估计检测限和定量限分别为300和800 ppm。对于1 wt.%的K，K校准的1σ相对不确定度为20 K2 O和40%（3000 ppm K2 O）。如果对35亿年来含1和0.3wt.%的岩石测量Ar的量，误差为15%，K_2O，K-Ar年龄的1σ误差分别为10%和20%。这种精确度将大大改善目前火星年表的不确定性，其不确定性约为2到4倍。这些结果表明，K的浓度可以在高真空条件下定量测量，使用组合的仪器，以前在行星任务中进行，这表明建设现场等时线K-Ar定年仪器LIBS的可行性。
We conducted a series of laser induced breakdown spectroscopy (LIBS) experiments for K measurements under high vacuum conditions (10- 6Pa) for the purpose of developing in-situ isochron type K–Ar dating instruments for planetary missions. Unlike whole rock measurement methods, isochron measurements require LIBS experiments in a vacuum chamber because simultaneous Ar isotopic measurements are necessary. However, detailed examination of detection limits and accuracy of this method at low pressures has not been examined extensively before. In this study, the capability of K measurements under high vacuum conditions was examined using LIBS. A compact Czerny-Turner type spectrometer equipped with a charge-coupled device (CCD) as a detector was employed. Twenty-three geologic standard samples were measured using the LIBS method. The second strongest K emission line at 769.89 nm was used for calibration because the strongest emission line at 766.49 nm may suffer from strong interference from another emission line. A calibration curve was constructed for K using internal normalization with the oxygen line at 777 nm and well fitted by a power-law function. Based on the prediction band method, the detection limit and the quantitation limit were estimated to be 300 and 800 ppm, respectively. The 1σ relative uncertainty of the K calibration was 20% for 1 wt.% K2O and 40% for 3000 ppm K2O. If the amount of Ar is measured with 15% error for the 3.5 billion years rocks containing 1 and 0.3 wt.% K2O, the K–Ar ages would be determined with 10% and 20% 1σ errors, respectively. This level of precision will significantly improve the current Martian chronology, which has uncertainty about a factor of two to four. These results indicate that the concentration of K can be measured quantitatively under high vacuum conditions using a combination of instruments that have previously been carried in planetary missions, which suggests the viability of building in situ isochron K–Ar dating instruments with LIBS.