微堆超热中子活化分析在地学样品测定中的应用

微型中子源反应堆(简称微堆)是以高浓铀(235 U)作燃料的轻水欠慢化型反应堆,辐照孔道内存在有较大份额的超热中子和快中子,适合进行超热中子活化分析(ENAA)的实验研究。地质样品成分复杂,在用普通的中子活化分析时,基体元素影响了部分元素的准确测定。为降低基体成分的本底干扰、改善目标元素的测量精密度和检出限,可采用超热中子活化分析的方法。本文利用微堆上安装的屏蔽材料为镉的超热中子辐照孔道,测定了元素周期表中67种元素的约130个核素的镉比,讨论了在超热中子活化分析中某些元素的有利因子及铀裂变和(n,p)反应的干扰情况,验证了微堆ENAA方法在地质科学样品检测中的实际应用,证实利用本方法可测定地学样品中20余种元素,其检出限、精密度和准确度均得到了较明显的改善。该法是常规活化分析方法必要的、有益的补充。

Application of MNSR Epithermal Neutron Activation Analysis in Determination of Geological Sample

The miniature neutron source reactor (MNSR) is based on highly enriched uranium (²³⁵U) as fuel and light water as moderator. Because of a larger share of epithermal neutron and fast neutron in irradiation channel, the reactor is suitable for epithermal neutron activation analysis (ENAA). In general neutron activation analysis the main component elements in complex geological samples such as aluminum, sodium, iron and so on affect the determination accuracy of some target elements. In order to reduce the interference of the background of main component elements and improve the precision and detection limit of the target element, the ENAA can be used in the test of geological samples. By using epithermal neutron irradiation channel made of cadmium, the Cd ratios of about 130 nuclides of 67 elements in the periodic table were measured. The advantage factors of some elements and the interferences of uranium fission and (n, p) reaction in ENAA were discussed. The practical application of MNSR ENAA method in testing of geological sample was verified. The results show that more than 20 kinds of elements can be ascertained in the sample measuring by this method. The detection limit, precision and accuracy are more significantly improved. The MNSR ENAA is a necessary and beneficial supplement of the conventional activation analysis method.