ASTM C1832-2016
利用热离子质谱仪的改进总蒸发 (MTE) 法测定铀同位素成分的标准试验方法

Standard Test Method for Determination of Uranium Isotopic Composition by the Modified Total Evaporation (MTE) Method Using a Thermal Ionization Mass Spectrometer

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标准号

ASTM C1832-2016

发布日期

2016年

实施日期

废止日期

无

发布单位

US-ASTM

适用范围

5.1x00a0;Uranium material is used as a fuel in certain types of nuclear reactors. To be suitable for use as nuclear fuel, the starting material shall meet certain specifications such as those described in Specifications C753, C776, C787, C833, C967, C996, and C1008, or as specified by the purchaser. The isotope amount ratios of uranium material can be measured by mass spectrometry following this test method to ensure that they meet the specification.

5.2x00a0;The MTE method can be used for a wide range of sample sizes even in samples containing as low as 50 x03bc;g of uranium. If the uranium sample is in the form of uranium hexafluoride, it can be converted into a uranium nitrate solution for measurement by the MTE method. The concentration of the loading solution for MTE has to be in the range of 1 to 6 mg/g to allow a sample loading of 2 to 6 x03bc;g of uranium. A minimum loading of 3 x03bc;g uranium per filament is recommended. This is needed to have a suitable ion signal especially for the two minor isotopes (²³⁴U and ²³⁶U) thus enabling the internal calibration of SEM versus the Faraday cups during the measurement.

5.3x00a0;Until now, the instrument capabilities for the MTE method have only been implemented on the TRITONx2122; TIMS instrument.5 Therefore all recommendations for measurement parameters in this test method are specified for the TRITONx2122; TIMS instrument. The manufacturers of other TIMS instruments (for example, IsotopX and Nu Instruments) have plans to implement the modifications needed in their instruments to use the MTE method.

5.4x00a0;The MTE method described here can also be extended to measurement of elements other than uranium. Note that the MTE method has already been implemented for plutonium and calcium.

1.1x00a0;This test method describes the determination of the isotope amount ratios of uranium material as nitrate solutions by the modified total evaporation (MTE) method using a thermal ionization mass spectrometer (TIMS) instrument.

1.2x00a0;The analytical performance in the determination of the ²³⁵U/²³⁸U major isotope amount ratio by MTE is similar to the (x201c;classicalx201d;) total evaporation (TE) method as described in Test Method C1672. However, in the MTE method, the evaporation process is interrupted on a regular basis to allow measurements and subsequent corrections for background form peak tailing, perform internal calibration of a secondary electron multiplier (SEM) detector versus the Faraday cups, peak centering, and ion source refocusing. Performing these calibrations and corrections on a regular basis during the measurement, improves precision, and significantly reduces uncertainties for the minor isotope amount ratios ²³⁴U/²³⁸U and ²³⁶U/²³⁸U as compared to the TE method.

1.3x00a0;In principle, the MTE method yields major isotope amount ratios without the......

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