液闪TDCR方法测量(55)^Fe核素活度  

Activity measurement of(55)^Fe using the liquid scintillation TDCR method

作　　者：刘皓然[1,2] 周倩倩 梁珺成[2] 袁大庆[1] LIU Haoran;ZHOU Qianqian;LIANG Juncheng;YUAN Daqing(China Institute of Atomic Energy,Beijing 102413,China;National Institute of Metrology,Beijing 100029,China)

机构地区：[1]中国原子能科学研究院,北京102413 [2]中国计量科学研究院,北京100029

出　　处：《核技术》2023年第1期64-71,共8页Nuclear Techniques

摘　　要：为准确测量(55)^Fe核素活度,本研究采用液闪三双符合比(Triple-to-double Coincidence Ratio,TDCR)方法,首先根据(55)^Fe的核衰变与原子壳层数据,应用随机原子重排模型计算得到(55)^Fe在闪烁液中的电子沉积谱,其次基于自由参数模型计算单能电子在液闪中的计数效率,然后对所有沉积电子的效率进行求和得到(55)^Fe的总效率曲线,最后通过实验测量TDCR值,并结合总效率曲线导出实验计数效率,从而实现(55)^Fe活度的绝对测量。实验观测到光电倍增管(Photomultiplier Tube,PMT)量子效率非对称效应,各样品的修正因子在1.001~1.005之间。(55)^Fe比活度测量结果为94.15 kBq·g^(-1),相对标准不确定度为0.45%。结果表明:液闪TDCR方法测量(55)^Fe可得到较低的相对标准不确定度。液体闪烁计数器对(55)^Fe具有较高的探测效率,两管符合逻辑相加效率达到63%以上。考虑PMT量子效率非对称修正后,得到了更一致的结果。[Background](55)^Fe is a low-energy radionuclide that is difficult to measure and decays to a ground state of55Mn through pure electron capture(EC),accompanied by the emission of Auger electrons and low-energy X-ray.As iron is the main component of nuclear reactor building materials,significant amounts of(55)^Fe have been produced in nuclear reactors and other neutron-producing nuclear facilities.[Purpose]This study aims to develop an(55)^Fe nuclide standard through the absolute measurement of(55)^Fe activity and provides activity traceability services for(55)^Fe measuring instruments to ensure the accuracy and consistency of the measurement results of calibration instruments.[Methods]The liquid scintillation triple-to-double coincidence ratio(TDCR)method was applied to determining the activity of(55)^Fe.First,based on nuclear and atomic data of(55)^Fe,the electron deposition spectrum of(55)^Fe in a scintillator was calculated using a random atomic rearrangement model.Second,the counting efficiency of singleenergy electron was computed based on the free parameter model.The total efficiency curve of(55)^Fe was then obtained by summing the efficiency of all deposited electrons.Finally,the experimental counting efficiency was derived by measuring the TDCR value and combining it with the total efficiency curve to realize an absolute measurement of(55)^Fe activity.[Results]The experimental results show that correction factors for the asymmetric effect of photomultiplier tube(PMT)quantum efficiency obtained on test samples are between 1.001 and 1.005.The measured specific activity of(55)^Fe is 94.15 k Bq·g^(-1)with a relative standard uncertainty of 0.45%.Experimental efficiency is better than 63%for double coincidence logic sum of liquid scintillation counter.[Conclusions]This study demonstrates that low relative standard uncertainty of(55)^Fe activity could be achieved using the liquid scintillation TDCR method with high detection efficiency,and more consistent measurement results can be obtained after applying the

关 键 词：放射性核素计量 (55)^Fe 液体闪烁计数 液闪三双符合比 

分 类 号：TL84[核科学技术—核技术及应用]