1.1 该试验方法包括通过活化反应测量反应速率的程序 27 Al（n，α） 24 不。 1.2 这种活化反应可用于测量能量超过约6.5MeV的中子，以及长达约两天的辐照时间（对于较长的辐照，或当辐照期间反应堆功率有显著变化时，请参阅实践 第261页 )。 1.3 使用合适的技术，裂变中子注量率高于10 6. 厘米 −2 ·秒 −1 可以确定。 1.4 实践中参考了其他快中子探测器的详细程序 第261页 。 1.5 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。 1.6 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====== 5.1 请参阅指南 电子844 用于中子剂量计的选择、辐照和质量控制。 5.2 参考实践 第261页 用于用阈值探测器测定快中子注量率的一般讨论。 5.3 箔或金属丝形式的纯铝很容易获得并易于处理。 27 Al的丰度为100% ( 1. ) 。 3. 5.4 24 Na的半衰期为14.958（2） 4. 小时 ( 2. ) 并发射能量为1.368630（5）和2.754049（13）MeV的伽马射线 ( 2. ) 。 5.5 图1 显示了国际反应堆剂量测定和聚变文件（IRDFF-II）的横截面图 ( 3. ， 4. ) 快中子反应的中子能量 27 Al（n，α） 24 钠 ( 3. ) 以及与当前实验数据库的比较 ( 5. ， 6. ) 虽然RRDF-2008和IRDFF-1.05的横截面从阈值延伸至60 MeV，但由于考虑到可用的验证数据，本标准建议在反应堆剂量测定应用中使用该横截面的能量区域仅从~4的阈值延伸。 25兆电子伏至20兆电子伏。此图用于说明，用于指示 27 Al（n，α）反应。请参阅指南 2018年1月 表中剂量测定横截面的推荐来源。 图1 27 Al（n，α） 24 Na横截面，来自IRDFF-II库，带有EXFOR实验数据 5.6 两个相互竞争的活动， 28 Al（2.25（2）分钟半衰期）和 27 Mg（9.458（12）分钟半衰期）在反应中形成 27 Al（n，γ） 28 Al和 27 Al（n，p） 27 Mg，但这些可以通过在计数前等待2小时来消除。

1.1 This test method covers procedures measuring reaction rates by the activation reaction 27 Al(n,α) 24 Na. 1.2 This activation reaction is useful for measuring neutrons with energies above approximately 6.5 MeV and for irradiation times up to about two days (for longer irradiations, or when there are significant variations in reactor power during the irradiation, see Practice E261 ). 1.3 With suitable techniques, fission-neutron fluence rates above 10 6 cm −2 ·s −1 can be determined. 1.4 Detailed procedures for other fast neutron detectors are referenced in Practice E261 . 1.5 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. 1.6 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 Refer to Guide E844 for the selection, irradiation, and quality control of neutron dosimeters. 5.2 Refer to Practice E261 for a general discussion of the determination of fast-neutron fluence rate with threshold detectors. 5.3 Pure aluminum in the form of foil or wire is readily available and easily handled. 27 Al has an abundance of 100 % ( 1 ) . 3 5.4 24 Na has a half-life of 14.958 (2) 4 h ( 2 ) and emits gamma rays with energies of 1.368630 (5) and 2.754049 (13) MeV ( 2 ) . 5.5 Fig. 1 shows a plot of the International Reactor Dosimetry and Fusion File (IRDFF-II) cross section ( 3 , 4 ) versus neutron energy for the fast-neutron reaction 27 Al(n,α) 24 Na ( 3 ) along with a comparison to the current experimental database ( 5 , 6 ) . While the RRDF-2008 and IRDFF-1.05 cross sections extend from threshold up to 60 MeV, due to considerations of the available validation data, the energy region over which this standard recommends use of this cross section for reactor dosimetry applications only extends from threshold at ~4.25 MeV up to 20 MeV. This figure is for illustrative purposes and is used to indicate the range of response of the 27 Al(n,α) reaction. Refer to Guide E1018 for recommended sources for the tabulated dosimetry cross sections. FIG. 1 27 Al(n,α) 24 Na Cross Section, from IRDFF-II Library, with EXFOR Experimental Data 5.6 Two competing activities, 28 Al (2.25 (2) minute half-life) and 27 Mg (9.458 (12) minute half-life), are formed in the reactions 27 Al(n,γ) 28 Al and 27 Al(n,p) 27 Mg, respectively, but these can be eliminated by waiting 2 h before counting.