1.1 本试验方法描述了使用热电离质谱仪（TIMS）仪器，通过双峰（DS）法测定硝酸盐溶液中铀材料的同位素量比。 1.2 测定的分析性能 235 U/ 238 在内部和外部再现性方面，与试验方法中所述的（“经典”）全蒸发（TE）方法相比，DS方法的U主同位素量比要高出5到10倍 C1672 以及试验方法中所述的“修正总蒸发”（MTE） C1832 . 这是由于使用了 内部的 而不是 外部的 使用已知或经认证的双尖峰材料进行质量分馏校正 233 U/ 236 U同位素比值，在样品制备过程中或直接在TIMS灯丝上测量之前与样品混合。 1.3 DS方法不能用于确定 236 U/ 238 U微量同位素量比，也不建议用于测定 234 U/ 238 铀微量同位素量比。 1.4 如果已知或证明双尖峰的铀量浓度，则可以使用测试方法中所述的同位素稀释质谱法（IDMS）测定样品的铀量浓度 C1672 ，通过重量法将样品与双尖峰混合，并进行DS测量。 1.5 根据TE的建议和MTE测量的要求，通过测量加载在不同灯丝上并在相同测量序列中测量的认证标准物质进行外部质量分馏校正，对于DS方法来说是不必要的。然而，出于质量控制（QC）目的，建议定期对低浓缩铀或天然铀同位素标准物质进行DS测量。 1.6 DS方法仅适用于具有相对同位素丰度的铀样品 233 U/U低于10 –5 和 236 U/U低于5×10 –4 因此，DS方法主要用于低浓缩铀或接近天然铀的样品。 1.7 单位- 以国际单位制表示的数值应视为标准。如果未提供国际单位制，则这些值仅供参考。 1.8 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.9 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 铀材料在某些类型的核反应堆中用作燃料。为了适合用作核燃料，起始材料应符合某些规范，如规范中所述 C753 , C776 , C787 , C833 , C967 , C996 和 C1008 或由买方指定。这个 235 U/ 238 铀同位素量比和铀材料的量含量可根据本试验方法通过质谱法测量，以确保其符合规范。 5.2 双峰法已用于同位素地球化学和宇宙化学中铀分馏效应的研究，核取证中铀源的归属，以及核工业和核保障中转换或采样过程的调查 ( 7- 11 ) . 最近，双峰法已用于验证超滤膜的Cristallini采样方法 6. ( 12和 13 ) . 即使在铀含量低至50μg的样品中，双峰法也可用于大范围的样品尺寸。DS方法的加载溶液浓度必须在1至6 mg/g范围内，以允许4至6μg铀的样品加载。建议每个灯丝的最小负载量为4μg铀。 5.3 测量 236 U/ 238 由于来自该方法的较大等压干扰，因此不可能使用该方法进行U比率 236 双尖峰的U离子束 236 样品中的U离子束（>50.000次，例如，对于接近天然的材料，如IRMM-184）。 5.4 双尖峰法在激光测量中的应用 235 U/ 238 U比受以下因素之间的等压干扰限制: 236 U来自双尖峰材料和 236 样品中含有U。因此，该方法不适用于含有大量 236 U由于之前的中子俘获 235 U在先前的材料中。对于带有 236 U/ 238 U比率高于10左右 –6 ，应用双峰法时应注意等压校正。为了进行适当的等压校正 236 U/ 238 应使用合适的测量方法，例如改进的总蒸发MTE法（试验方法），单独测定样品的U比 C1832 ，参考 ( 5. ) 和 ( 6. ) ). 5.5 测量 234 U/ 238 由于样品的等压干扰，使用该方法的U比值在分析性能上非常有限 234 U从双尖刺开始 234 样品中的U（范围从5到15 %). 校正算法见 14.3 ，但未给出精度和偏差的说明。其他方法，如MTE（试验方法 C1832 ，参考 ( 5. ) 和 ( 6. ) )更适合和更可靠地测量 234 U/ 238 U比率。 5.6 如果有合适的双尖峰材料，此处描述的直接谱方法也可以扩展到铀以外的元素的测量。

1.1 This test method describes the determination of the isotope amount ratios of uranium material as nitrate solutions by the double spike (DS) method using a thermal ionization mass spectrometer (TIMS) instrument. 1.2 The analytical performance in the determination of the 235 U/ 238 U major isotope amount ratio by the DS method is five to ten times better in terms of the internal and external reproducibility compared to the (“classical”) total evaporation (TE) method as described in Test Method C1672 and the “modified total evaporation” (MTE) as described in Test Method C1832 . This is due to the use of an internal rather than external mass fractionation correction by using a double spike material with a known or certified 233 U/ 236 U isotope ratio, which is mixed with the sample prior to the measurement, either during the sample preparation or directly on the TIMS filament. 1.3 The DS method cannot be applied for the determination of the 236 U/ 238 U minor isotope amount ratio, and is also not recommended for the determination of the 234 U/ 238 U minor isotope amount ratio. 1.4 In case the uranium amount concentration of the double spike is known or certified, the uranium amount concentration of the sample can be determined using the isotope dilution mass spectrometry (IDMS) method as described in Test Method C1672 , by blending the sample gravimetrically with the double spike and performing a DS measurement. 1.5 An external mass fractionation correction by measurements of a certified reference material loaded on different filaments and measured in the same measurement sequence, as recommended for TE and required for MTE measurements, is not necessary for the DS method. However, for quality control (QC) purposes it is recommended to perform DS measurements of low enriched or natural uranium isotopic reference materials on a regular basis. 1.6 The DS method can only be applied to uranium samples with relative isotope abundances 233 U/U below 10 –5 and 236 U/U below 5 × 10 –4 , the DS method is therefore mainly used for low enriched or close to natural uranium samples. 1.7 Units— The values stated in SI units are to be regarded as the standard. When no SI units are provided, the values are for information only. 1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 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 235 U/ 238 U isotope amount ratios and the amount content of uranium material can be measured by mass spectrometry following this test method to ensure that they meet the specification. 5.2 The double spike method has been used for studies of uranium fractionation effects in isotope geochemistry and cosmochemistry, for uranium source attribution in nuclear forensics and for investigation of conversion or sampling processes in nuclear industry and nuclear safeguards ( 7- 11 ) . Most recently, the double spike method has been used for the validation of the Cristallini sampling method of UF 6 ( 12 and 13 ) . The double spike method can be used for a wide range of sample sizes even in samples containing as low as 50 μg of uranium. The concentration of the loading solution for the DS method has to be in the range of 1 to 6 mg/g to allow a sample loading of 4 to 6 μg of uranium. A minimum loading of 4 μg uranium per filament is recommended. 5.3 The measurement of 236 U/ 238 U ratios using this method is not possible due to the large isobaric interference from the 236 U ion beam of the double spike onto the 236 U ion beam from the sample (>50.000 times for close to natural material, for example, like IRMM-184). 5.4 The application of the double spike method for measurements of 235 U/ 238 U ratio is limited by the isobaric interference between the 236 U from the double spike material and the 236 U contained in the sample. As a consequence, the method is not suitable for samples which contain significant amounts of 236 U due to prior neutron capture from 235 U in the predecessor materials. For samples with 236 U/ 238 U ratios higher than about 10 –6 , the double spike method should be applied with care for the isobaric correction. For an appropriate isobaric correction, the 236 U/ 238 U ratios of the samples should be determined separately using a suitable measurement method, for example, the modified total evaporation MTE method (Test Method C1832 , Ref ( 5 ) and ( 6 ) ). 5.5 The measurement of 234 U/ 238 U ratios using this method is very limited in the analytical performance due to the isobaric interference of the 234 U from the double spike with the 234 U from the sample (range from 5 to 15 %). The correction algorithms are presented in 14.3 , but statements for precision and bias are not given. Other methods like MTE (Test Method C1832 , Ref ( 5 ) and ( 6 ) ) are better suited and more reliable for measurements of 234 U/ 238 U ratios. 5.6 The DS method described here can also be extended to measurement of elements other than uranium, if a suitable double spike material is available.