1.1 该试验方法的目的是定义通过中子活化技术确定未知热中子注量率的通用程序。完全描述一种适用于大量需要测量热中子注量率的实验情况的技术是不可行的。因此，提出这种方法是为了让用户能够适应他们的特定情况——以下技术的基本过程。 1.1.1 使用纯钴、纯金、纯铟、钴铝、合金、金铝合金或铟铝合金的放射计数技术。 1.1.2 使用纯金或金铝合金的标准比较技术，以及 1.1.3 使用纯铟、铟铝合金、纯镝或镝铝合金的二次标准比较技术。 1.2 所介绍的技术仅限于在室温下进行测量。然而，在高温下进行热中子注量率测量时的特殊问题- 温度环境在中进行了讨论 9.2 对于那些由于潜在的光谱扰动或镉熔点以上的温度而不希望使用镉作为热屏蔽的情况，实践中描述的方法 E481 在某些情况下可以使用。或者，可以使用钆过滤器代替镉。对于铝合金不适用的高温应用，已经使用了诸如钴镍或钴钒的其他合金。 1.3 该测试方法可用于确定等效2200 m/s注量率。实际热中子注量率的准确测定需要了解中子温度，中子温度的测定不在标准范围内。 1.4 所提出的技术仅适用于具有显著热中子组分的中子场，其中存在缓和材料，并且与热中子能量范围内的平均吸收截面相比，平均散射截面大。 1.5 表1 表示每种探测器材料的有用中子注量范围。 1.6 本标准并不旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者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。 1.7 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 ====意义和用途====== 4.1 这种测试方法可以扩展到使用任何具有必要的核特性和活化特性的材料，以适应实验者的特殊情况。没有人试图完全描述计数技术、中子注量下降和厚箔自身的无数问题- 屏蔽。假设实验者将参考关于这些主题的现有文献。这种测试方法确实提供了一种裁判技术（标准金箔），当实验者怀疑他们是否有能力以足够的精度执行辐射测量技术时，可以帮助他们。 4.2 标准比较技术使用一组在形状和质量上尽可能接近相同的箔。箔由任何通过( n、 γ )反应，优选具有与热能范围内的中子速度近似成反比的横截面。一些箔片在已知的中子场中照射（在NIST或其他标准实验室）。箔片在稳定的辐射探测仪器上以固定的几何形状进行计数。根据计数数据计算箔的中子诱导反应速率，并确定已知中子注量速率与计算反应速率的比率。 对于任何给定的箔片、中子能谱和计数装置，这个比率都是常数。同一组中的其他箔片现在可以暴露在未知的中子场中。通过比较根据未知场和参考场的计数数据确定的反应速率，以及考虑两个场之间光谱差异的适当校正，可以获得未知场中注量率的大小（见第节 5. ). 该技术的一个重要特征是它消除了知道检测器效率的需要。 4.3 该试验方法遵循Stoughton和Halperin报告热中子注量的约定。其他公约是韦斯科特公约（在实践中遵循 E481 )和霍格达尔公约。实践 E261 解释了这三种约定，并给出了与由不同约定确定的值相关的转换公式。参考 ( 1. ) 3. 详细讨论了三种热中子约定。

1.1 The purpose of this test method is to define a general procedure for determining an unknown thermal neutron fluence rate by neutron activation techniques. It is not practicable to describe completely a technique applicable to the large number of experimental situations that require the measurement of a thermal neutron fluence rate. Therefore, this method is presented so that the user may adapt to their particular situation the fundamental procedures of the following techniques. 1.1.1 Radiometric counting technique using pure cobalt, pure gold, pure indium, cobalt-aluminum, alloy, gold-aluminum alloy, or indium-aluminum alloy. 1.1.2 Standard comparison technique using pure gold, or gold-aluminum alloy, and 1.1.3 Secondary standard comparison techniques using pure indium, indium-aluminum alloy, pure dysprosium, or dysprosium-aluminum alloy. 1.2 The techniques presented are limited to measurements at room temperatures. However, special problems when making thermal neutron fluence rate measurements in high-temperature environments are discussed in 9.2 . For those circumstances where the use of cadmium as a thermal shield is undesirable because of potential spectrum perturbations or of temperatures above the melting point of cadmium, the method described in Practice E481 can be used in some cases. Alternatively, gadolinium filters may be used instead of cadmium. For high-temperature applications in which aluminum alloys are unsuitable, other alloys such as cobalt-nickel or cobalt-vanadium have been used. 1.3 This test method may be used to determine the equivalent 2200 m/s fluence rate. The accurate determination of the actual thermal neutron fluence rate requires knowledge of the neutron temperature, and determination of the neutron temperature is not within the scope of the standard. 1.4 The techniques presented are suitable only for neutron fields having a significant thermal neutron component, in which moderating materials are present, and for which the average scattering cross section is large compared to the average absorption cross section in the thermal neutron energy range. 1.5 Table 1 indicates the useful neutron fluence ranges for each detector material. 1.6 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. 1.7 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 ====== 4.1 This test method can be extended to use any material that has the necessary nuclear and activation properties that suit the experimenter's particular situation. No attempt has been made to fully describe the myriad problems of counting techniques, neutron fluence depression, and thick foil self-shielding. It is assumed that the experimenter will refer to existing literature on these subjects. This test method does offer a referee technique (the standard gold foil) to aid the experimenter when they are in doubt of their ability to perform the radiometric technique with sufficient accuracy. 4.2 The standard comparison technique uses a set of foils that are as nearly identical as possible in shape and mass. The foils are fabricated from any material that activates by an ( n, γ ) reaction, preferably having a cross section approximately inversely proportional to neutron speed in the thermal energy range. Some of the foils are irradiated in a known neutron field (at NIST or other standards laboratory). The foils are counted in a fixed geometry on a stable radiation-detecting instrument. The neutron-induced reaction rate of the foils is computed from the counting data, and the ratio of the known neutron fluence rate to the computed reaction rate is determined. For any given foil, neutron energy spectrum, and counting setup, this ratio is a constant. Other foils from the identical set can now be exposed to an unknown neutron field. The magnitude of the fluence rate in the unknown field can be obtained by comparing the reaction rates as determined from the counting data from the unknown and reference field, with proper corrections to account for spectral differences between the two fields (see Section 5 ). One important feature of this technique is that it eliminates the need for knowing the detector efficiency. 4.3 This test method follows the Stoughton and Halperin convention for reporting thermal neutron fluence. Other conventions are the Wescott convention (followed in Practice E481 ) and the Hogdahl convention. Practice E261 explains the three conventions and gives conversion formulae relating values determined by the different conventions. Reference ( 1 ) 3 discusses the three thermal neutron conventions in detail.