多节点微口袋裂变电离室信号串扰的抑制

Signal Crosstalk Suppression of Multi-node Micro-pocket Fission Detector

  • 摘要: 微口袋裂变电离室(micro-pocket fission detector, MPFD)是堪萨斯州立大学提出的一种新型微型裂变电离室,通过组合多个探测器形成一个多节点的探测器阵列,用于核反应堆堆芯中子注量率的三维在线监测或辐照样品处中子注量率的原位在线监测。在多节点探测器的设计过程中,由于各节点用于施加电场和输出信号的平行导线距离非常近,必须抑制各节点之间产生信号的相互串扰,以获得各节点输出信号的准确信息。本工作提出了一种3节点的MPFD设计,利用Garfiled、SRIM以及有限元分析方法对MPFD不同节点之间的串扰信号进行模拟分析,结果表明,MPFD串扰信号较主信号低1个量级,且极性相反。同时,制做了3节点的MPFD探测器样机,利用235U自发衰变产生的α粒子对两个节点之间的串扰信号进行了实验测试。实验结果与模拟计算结果一致,表明这种3节点的MPFD,由不同节点产生的串扰信号可通过信号极性和脉冲幅度进行甄别,不影响探测器对中子注量率的测量。

     

    Abstract: For a long time, the micro-neutron detector, which is capable of withstanding the nuclear reactor core environment, has been a research hotspot in related fields. The micro-pocket fission detector (MPFD), which was proposed Kansas State University, is fabricated with microalumina ceramic substrates which are capable of withstanding high temperature and high flux environment. The size of the substrates is only in millimeter scale. This micro-size allows multiple MPFDs to be assembled into an array of detectors to facilitate 3-D mapping of a reactor core neutron flux profile in real-time. For the multi-node MPFD constructed of parallel wire electrodes and substrates, every readout electrode is near each other due to its small size. When the detector structure design is unreasonable, certain signal crosstalk will occur between nodes, that is, the charged particle emitted in one node will often generate similar signals not only on the readout electrode of this node, but also on the corresponding electrodes of other nodes in the MPFD. The crosstalk may cause the fission counting rate of the detector exceed the fission frequency (pulse mode) or current amplitude of the detector distort (current mode and MSV mode), thus decreasing the accuracy of the neutron flux measured by MPFD. Therefore, whether the crosstalk can be reduced is an important index to evaluate the performance of this multinode MPFD detector. The amplitude of crosstalk signal is affected by the structure of the detector. Numerical simulation on the polarity and pulse amplitude of crosstalk signal can provide theoretical guidance for the design of MPFD detector. In this work, a 3-node MPFD design was proposed. Garfiled, SRIM and finite element analysis method were used to simulate and analyze crosstalk signals between different MPFD nodes. The results show that crosstalk signal is one order of magnitude lower than main signal, and the polarity is opposite. At the same time, a 3-node MPFD detector prototype was made. Crosstalk signal generated by α particle emitted from the uranium coating was tested experimentally. The experimental results are consistent with the simulation results, which shows that crosstalk signal between different nodes in this 3-node MPFD can be distinguished by signal polarity and pulse amplitude, so it will not affect the measurement of neutron flux.

     

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