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A well-type detector is described for the assay of gamma emitters over a Curie-to-nanoCurie activity range. A large plastic scintillator/photomultiplier is DC-coupled for current measurements at high activities, with pulse counting covering the low activities. The two techniques overlap for two decades in the uCi region, particularly troublesome for the alternative detectors: gas-filled ionization chambers or NaI(Tl) well counters. The plastic well is interfaced to a microcomputer for data acquisition and control of the phototube high voltage, the key to the nine-decade dynamic range. 相似文献
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宽量程中子探测靶室 总被引:1,自引:1,他引:0
马驰 《核电子学与探测技术》1995,15(6):373-376
通过对反冲质子法探测强脉冲高能中子靶室系统灵敏度的理论研究与计算,可使探测靶室的系统灵敏度从1O ̄(-27)~10 ̄(18)(A·s·cm ̄(2))连续变化,计算精度符合要求。 相似文献
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The expectation maximization (EM) algorithm for the maximum likelihood (ML) image reconstruction criterion generates severe checkerboard artifacts in the presence of noise. A classical remedy is to impose an a priori constraint for a penalized ML or maximum a posteriori probability solution. The penalty reduces the checkerboard artifacts and also introduces uncertainty because a priori information is usually unknown in clinic. Recent theoretical investigation reveals that the noise can be divided into two components: one is called null-space noise and the other is range-space noise. The null-space noise can be numerically estimated using filtered backprojection (FBP) algorithm. By the FBP algorithm, the null-space noise annihilates in the reconstruction while the range-space noise propagates into the reconstructed image. The aim of this work is to investigate the relation between the null-space noise and the checkerboard artifacts in the ML-EM reconstruction from noisy projection data. Our study suggests that removing the null-space noise from the projection data could improve the signal-to-noise ratio of the projection data and, therefore, reduce the checkerboard artifacts in the ML-EM reconstructed images. This study reveals an in-depth understanding of the different noise propagations in analytical and iterative image reconstructions, which may be useful to single photon emission computed tomography, where the noise has been a major factor for image degradation. The reduction of the ML-EM checkerboard artifacts by removing the null-space noise avoids the uncertainty of using a priori penalty. 相似文献
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本文介绍了直读式双量程真空室剂量仪的历史背景、基本结构、工作原理和性能特点。对剂量率效应这一关键性能做了简单的计算和验证。 相似文献
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反应堆启动初始阶段,中子注量非常低,是一般核测量系统的测量盲区。针对测量盲区的问题,设计了一种高灵敏度宽量程的中子注量率探测器。通过计算及实验表明,该探测器具有稳定的性能,能提供一种反应堆物理启动过程中盲区中子注量率测量的方法。 相似文献
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GM计数管是一种应用广泛的核辐射探测器,但量程范围较窄,扩展其量程能进一步拓宽其应用范围.回顾了国内外扩展GM计数管量程所采取的主要方法和措施,分析了采用死时间模型和函数拟合修正方法扩展量程存在的不足;简要介绍和分析了改变计数管工件方式或改进外部电路的量程扩展方法,重点介绍了近年来出现的time-to-count方法的工作原理.指出通过革新使用方式,改进计数管结构设计和筛选恰当材料,研制复合型探测器等途径,可大幅提高计数管的性能. 相似文献
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为满足用同一放射性区域监测系统监控高低剂量率的需求,研制了一套宽量程放射性区域监测系统。该系统采用2支不同量程的G-M管切换技术进行区域辐射监测,实现了1×10-7~1 Gy/h宽量程放射性区域监控。测试结果表明:该系统测量0.5μGy/h时,其相对标准偏差不大于2%;测量1Gy/h时,其相对标准偏差不大于0.5%;系统长期稳定性优于1.5%,可有效地满足区域辐射监测需求。 相似文献