LRAD管道内两面源的放射性测量技术

Radioactive measurement technology of two-surface source based on LRAD inside pipes

针对核设施退役管道中多点或大面积污染情况,采用自主研制的新型长距离α探测技术(LRAD)测量系统,开展了管道中不同参数下两面源(不同核素、不同面活度的α面源)污染影响特征的对比实验。实验结果表明:两面源相对间距为10 cm时,探测效率均高于相对间距为0 cm、20 cm、40 cm三种情况,与理论分析相吻合;241Am源距电离室近、239Pu源距电离室远的测量结果大于两面源前后位置颠倒的测量结果;两个面源同时测量值小于两个面源在相应位置单独测量值之和。所以多面源对LRAD测量值具有一定的影响规律,可为管道内α核素污染测量研究提供一定的技术参考价值。

Background： The development of measuring technologies of radioactive contamination becomes more and more important. Long Range Alpha Detector （LRAD） can effectively solve some problems such as the short ranges of alpha particles, weak penetration ability and so on. LRAD also has advantages that the alpha radioactivity of interior surface of irregular pipes or just irregular surface can be measured nondestructively and precisely. Purpose： This paper attempts to obtain the measured value of multi-point sources and large contamination areas in pipes. And the comparative experiments of impact factors of two different radioactive surface sources （different nuclides and radioactivities） have been done. Methods： In the experiment, a new domestic LRAD is utilized to measure the alpha activity of interior surface of steel pipes. Here, the inner diameter of pipes is 78 nun and there are two kinds of pipes： straight pipe and U-bend pipe. The radioactive sources include 241AlTI （3 772.2 Bq） and 239pu （224.4 Bq）. The distance between different sources takes values of 0 cm, 10 cm, 20 cm and 40 cm, respectively, and the distance between the whole mixed radioactive source and detector increases by step of 20 cm. Results： When the relative distance of the two surface sources is 10 cm, the detection efficiency of LRAD is higher than that of relative distance of 0 cm, 20 cm and 40 cm, which matches the result of theoretical analysis. When 241Am is closer to the detector than 239pu, measuring results are much higher than those of the opposite situation. And in the same position, when the two sources are put together, the measured results are lower than those of the sum of each single source. Conclusion： Based on the experimental results, a self-developed new LRAD measurement system has been used to measure two non-point sources in pipes.