微堆循环中子活化分析方法的建立与应用

Establishment and application of the cyclic neutron activation analysis method on mini-reactor

仪器中子活化分析是一种非破坏性的分析方法。一些元素辐照后产生短半衰期(<60 s)放射性核素,其他元素既产生长寿命核素也产生短寿命核素。这些短寿命核素,单次测量误差较大。为了减少误差,提高灵敏度,可采用循环中子活化分析的方法。通过一个连接到样品传送器、探测器以及微型反应堆辐照管道,并可自动控制照射时间和计数时间的装置,根据某些元素的核参数,试验确定了照射时间、计数时间和循环周期次数,从而建立了基于微型堆的循环活化分析方法。研究了17种元素的循环活化分析条件,并应用于实际样品的测定。探讨了循环超热中子活化分析的方法实验。通过对国家标准参考物质的分析,证实了该方法的可靠性和灵敏度高、精度好、分析周期短的优点。循环中子活化分析是只有短寿命核素元素的有效分析方法,其精度优于单次短照活化分析。对同时有短寿命和长寿命核素的元素,该方法可以缩短分析周期,从几天到几周缩短至几分钟。

Background： Instrument neutron activation analysis is a nondestructive analytic method. Some elements after irradiation produce short half-life radio-nuclides （〈60 s）, and others produce both long-lived and short-lived nuclides. For these short-lived nuclides, the single measurement has big error. Purpose： In order to reduce the error, cyclic neutron activation analysis can be used to improve the sensitivity. Methods： A device was designed to be connected to the sample transporter, detector and irradiation pipeline in the reactor, which can automatically control the irradiation time and counting time. According to the nuclear parameters of certain elements, irradiation time and counting time and cycle times were determined by experiment. Cyclic activation analysis method was established at the mini-reactor. Results： This paper studied cyclic activation analysis conditions of 17 kinds of element, and applied to the determination of actual samples. Cyclic epithermal neutron activation analysis （CENAA） method was discussed too. By the analysis of national standard reference materials, the reliability of this method was confirmed. Conclusion： Cyclic neutron activation analysis （CNAA） is an effective analytic method for only short life nuclide elements. For both short and long lived nuclides of elements, the cyclic activation analysis method can make the analytical cycle shorten, from a few days or several weeks to within a few minutes. Cyclic activation analysis has the advantages of high sensitivity, and its precision and accuracy are better than single short irradiation activation analysis.