1.1 本试验方法描述了使用被动中子多重计数对金属、氧化物、废料、残渣或废物等形式的钚进行无损检测。该测试方法提供的结果通常比常规中子符合计数更准确。该方法可应用于各种容器中的各种钚项目，包括罐、208-L桶或1900-L标准废物箱。它已用于分析钚含量在1克到1000克之间的项目。 1.2 有几种电子学或数学方法可用于多重性分析，包括多重性移位寄存器、Euratom时间相关分析仪和列表模式模块，如Ref。 ( 1. ) . 2. 1.3 本试验方法主要用于测定 240 基于移位寄存器电子学矩的多重性分析 ( 1. , 2. , 3. ) 以及专门为多重性分析设计的高效中子计数器。 1.4 本试验方法需要了解钚同位素的相对丰度，以确定钚的总质量（见试验方法 C1030 ). 1.5 该试验方法也可用于改进的中子符合计数器 ( 4. ) 未专门设计为多重性计数器（即HLNCC、AWCC等），结果会相应降低。 1.6 以国际单位制表示的数值应视为标准值。本标准不包括其他计量单位。 1.7 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和健康实践，并确定监管限制的适用性。 ====意义和用途====== 5.1 本试验方法有助于测定杂质钚氧化物、混合钚/铀氧化物、氧化钚金属、钚废料和废物、钚工艺残留物和武器部件等项目的钚含量。 5.2 使用本试验方法进行的测量可能适用于保障措施或废物特性要求，例如: 5.2.1 核材料责任， 5.2.2 库存验证 ( 7. ) , 5.2.3 核材料含量的确认 ( 8. ) , 5.2.4 发货人/收货人差异的解决 ( 9 ) , 5.2.5 过剩武器材料检查 ( 10 , 11 ) , 5.2.6 废物防护终止 ( 12 , 13 ) , 5.2.7 裂变当量含量的测定 ( 14 ) . 5.3 中子多重性计数的一个重要特征是，由于第三个测量参数的可用性，它能够捕获比中子符合计数更多的信息，从而减少大多数材料类别的测量偏差，从而达到适当的精度。 该功能还可以对一些不符合传统重合计数的厂内材料进行分析，包括潮湿或不纯的氧化钚、氧化金属以及某些类别的废料、废物和残留物 ( 10 ) . 5.4 许多材料类型的校准不需要代表性标准。因此，该技术可用于无校准标准的库存验证 ( 7. ) ，但如果有代表性标准，测量偏差可能会更低。 5.4.1 由于计数统计，测量结果的重复性与核材料的数量、干扰中子和测量的计数时间有关 ( 15 ) . 5.4.2 对于某些材料，如小钚、小于1克的物品、一些含钚废物或非常不纯的钚工艺残留物，其中（α，n）反应速率压倒了三重信号，多重性信息可能没有用处，因为在实际计数时间内三重重合的计数统计较差 ( 12 ) . 5.5 对于纯钚金属、纯氧化物或其他具有良好特征的材料，不需要额外的多重性信息，传统的符合计数将提供更好的重复性，因为不使用三重符合的低计数统计。 传统的符合信息可以通过切换到符合分析器模式或在符合模式下分析多重性数据来获得。 5.6 中子多重性数据的数学分析基于以下几点假设，详见 附件A1 . 考虑的数学模型是空间中的一个点，假设中子探测效率、消失时间和乘法在整个项目中是恒定的 ( 16 , 17 ) . 随着测量偏离这些假设，偏差将增加。 5.6.1 被动式中子多重性测量中的偏差与“点模型”的偏差有关，例如探测效率、基质成分或项目内部核材料分布的变化。 5.6.2 核材料、中子慢化剂和中子吸收剂分布的不均匀性可能会引入影响结果准确性的偏差。在含量均匀的物品上进行的测量将比在含量不均匀的物品上进行的测量更准确。

1.1 This test method describes the nondestructive assay of plutonium in forms such as metal, oxide, scrap, residue, or waste using passive neutron multiplicity counting. This test method provides results that are usually more accurate than conventional neutron coincidence counting. The method can be applied to a large variety of plutonium items in various containers including cans, 208-L drums, or 1900-L Standard Waste Boxes. It has been used to assay items whose plutonium content ranges from 1 g to 1000s of g. 1.2 There are several electronics or mathematical approaches available for multiplicity analysis, including the multiplicity shift register, the Euratom Time Correlation Analyzer, and the List Mode Module, as described briefly in Ref. ( 1 ) . 2 1.3 This test method is primarily intended to address the assay of 240 Pu-effective by moments-based multiplicity analysis using shift register electronics ( 1 , 2 , 3 ) and high efficiency neutron counters specifically designed for multiplicity analysis. 1.4 This test method requires knowledge of the relative abundances of the plutonium isotopes to determine the total plutonium mass (See Test Method C1030 ). 1.5 This test method may also be applied to modified neutron coincidence counters ( 4 ) which were not specifically designed as multiplicity counters (that is, HLNCC, AWCC, etc), with a corresponding degradation of results. 1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.7 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 and health practices and determine the applicability of regulatory limitations prior to use. ====== Significance And Use ====== 5.1 This test method is useful for determining the plutonium content of items such as impure Pu oxide, mixed Pu/U oxide, oxidized Pu metal, Pu scrap and waste, Pu process residues, and weapons components. 5.2 Measurements made with this test method may be suitable for safeguards or waste characterization requirements such as: 5.2.1 Nuclear materials accountability, 5.2.2 Inventory verification ( 7 ) , 5.2.3 Confirmation of nuclear materials content ( 8 ) , 5.2.4 Resolution of shipper/receiver differences ( 9 ) , 5.2.5 Excess weapons materials inspections ( 10 , 11 ) , 5.2.6 Safeguards termination on waste ( 12 , 13 ) , 5.2.7 Determination of fissile equivalent content ( 14 ) . 5.3 A significant feature of neutron multiplicity counting is its ability to capture more information than neutron coincidence counting because of the availability of a third measured parameter, leading to reduced measurement bias for most material categories for which suitable precision can be attained. This feature also makes it possible to assay some in-plant materials that are not amenable to conventional coincidence counting, including moist or impure plutonium oxide, oxidized metal, and some categories of scrap, waste, and residues ( 10 ) . 5.4 Calibration for many material types does not require representative standards. Thus, the technique can be used for inventory verification without calibration standards ( 7 ) , although measurement bias may be lower if representative standards were available. 5.4.1 The repeatability of the measurement results due to counting statistics is related to the quantity of nuclear material, interfering neutrons, and the count time of the measurement ( 15 ) . 5.4.2 For certain materials such as small Pu, items of less than 1 g, some Pu-bearing waste, or very impure Pu process residues where the (α,n) reaction rate overwhelms the triples signal, multiplicity information may not be useful because of the poor counting statistics of the triple coincidences within practical counting times ( 12 ) . 5.5 For pure Pu metal, pure oxide, or other well-characterized materials, the additional multiplicity information is not needed, and conventional coincidence counting will provide better repeatability because the low counting statistics of the triple coincidences are not used. Conventional coincidence information can be obtained either by changing to coincidence analyzer mode, or analyzing the multiplicity data in coincidence mode. 5.6 The mathematical analysis of neutron multiplicity data is based on several assumptions that are detailed in Annex A1 . The mathematical model considered is a point in space, with assumptions that neutron detection efficiency, die-away time, and multiplication are constant across the entire item ( 16 , 17 ) . As the measurement deviates from these assumptions, the biases will increase. 5.6.1 Bias in passive neutron multiplicity measurements is related to deviations from the “point model” such as variations in detection efficiency, matrix composition, or distribution of nuclear material in the item's interior. 5.6.2 Heterogeneity in the distribution of nuclear material, neutron moderators, and neutron absorbers may introduce biases that affect the accuracy of the results. Measurements made on items with homogeneous contents will be more accurate than those made on items with inhomogeneous contents.