基于~(252)Cf中子源自相关分析的核事件死时间测量与修正方法

基于所研制的252Cf中子源频域测量系统,针对核探测系统的死时间使核事件丢失这一问题,利用自相关分析,研究了一种核探测系统死时间测量与修正的方法。试验测量结果表明:采用自相关图谱,可以直接获得高速频谱测量系统的死时间为40 ns,既方便又快捷,且测量精度高,达到了ns级,优于国外文献报道的类似核武器识别测量系统的死时间20μs。     

标记配对相干态下有限探测器死时间的测量设备无关量子密钥分配

量子密钥分配在实际应用中会受到有限探测器死时间的影响,当信号脉冲发送速率过大时,探测器测量失败的概率增加,安全密钥生成速率降低。对标记配对相干态光源下测量设备无关量子密钥分配的有限探测器死时间问题进行了分析。研究并仿真了安全密钥生成速率与信号发送速率的关系。考虑探测器死时间时,基于标记配对相干态光源的测量设备无关量子密钥分配协议的安全密钥生成速率比基于弱相干光源的测量设备无关量子密钥分配协议的安全密钥生成速率高。分析了有限探测器死时间τ分别为50,100,150 ns时安全密钥生成速率的情况。结果表明,有限探测器死时间越大,安全密钥生成速率的极限值越低。安全密钥生成速率的极限与有限探测器死时间的关系为8.1×10³/τ。     

单光子雪崩二极管的死时间效应分析

单光子雪崩二极管是一种采用盖革模式的单光子探测器件。一旦触发后探测器需要一段时间来重启,重启之后才能进行下一个光子事件的探测。重启所用时间(也叫死时间)的大小会影响探测器的光子计数分布。对单光子雪崩二极管的工作方式进行了数学建模,研究死时间对探测器输出响应的影响,推导出了在入射光子数服从泊松分布情况下探测器光子计数值的概率分布函数,并采用蒙特卡洛仿真进行了验证。结果表明死时间会使探测器输出的光子计数值减小,其分布会更加集中,并且死时间越大,入射光子速率越高,这种效应就越明显。     

HPGe γ谱仪系统死时间校正方法的实验研究

给出了HPGe γ谱仪系统死时间校正的一种实用方法. 用强源干扰找到了HPGe γ谱仪系统百分死时间与计数率丢失校正因子的关系, 使该系统允许计数率大大 提高, 从而解决了放射性定量测量中的一些困难.     

提高气体取样簇射计数器能量分辨率的实验研究

李文报告了最小电离β粒子在气体计数管中形成的正比、饱和正比和SQS信号谱, 指出了用SQS模式代替传统的正比模式气体取样簇射计数器以改善其能量分辨率的可能性. 对SQS的死时间、死空间测量的结果表明, 虽然它们对不同的气体成分数值有所不同, 但数量级相似, 典型值为死时间~10μs, 死空间~3 mm.     

X射线脉冲星导航系统导航精度的研究

为提高X射线脉冲星导航系统的导航精度,提出了一种基于低通滤波器的恒比定时方法,以提高X射线脉冲星导航系统中X射线脉冲到达时间的测量精度.通过设计测量方案,对原有的峰值定时方法和改进后的恒比定时系统的定时精度和死时间进行测量.测量结果表明,峰值定时系统的定时精度和死时间分别为18和4750 ns,恒比定时系统的定时精度和死时间分别为0.78和105 ns,与原有的峰值定时系统相比,采用恒比定时系统的定时精度和死时间均得到明显的提高.在X射线脉冲星导航系统中,通过利用这两种不同定时系统来测量X射线光子的到达时间以构造累积脉冲轮廓.实验结果表明,与峰值定时系统相比,采用改进的恒比定时系统获得的累积脉冲轮廓的信噪比得到明显改善,因此,采用恒比定时系统的导航精度可得到提高.     

用于脉冲星导航的X射线光子计数探测器研究

研制了用于脉冲星导航的X射线光子计数探测器原理样机, 该探测器主要由对X射线灵敏度较高的CsI光电阴极、微通道板电子倍增器和收集阳极组成. 对X射线光子计数探测器灵敏度、时间分辨率和整个系统的死时间进行了测试, 实验结果表明该探测器的灵敏度在5 keV时可达5.2× 10³ A/W, 时间分辨率可达到1.1 ns, 系统整体的死时间为100 ns. 关键词： 脉冲星导航 光子计数探测器 灵敏度 时间分辨率     

硅雪崩光电二极管单光子探测器

将硅雪崩光电二极管应用于盖革模式下,制作出高量子效率、低噪音、短死时间的单光子探测器.设计并制作了雪崩抑制电路,获得探测器特性参量为无源抑制方式下死时间1μs,有源抑制下60～80ns,输出脉冲宽度15～20ns.并详细检测了探测器直到液氮温度下的特性.观察到一些新现象.     

低场核磁共振短死时间射频线圈与射频开关的设计

本文以核磁共振（NMR）射频线圈振铃信号产生原理为对象进行分析研究,提出了一种适用于低场环境下由环状间隙腔线圈与螺线管线圈构成的收发分离式短死时间射频线圈设计方案,采用优化调谐匹配网络提高发射效率;根据射频线圈方案需求设计了快速切换的射频开关及驱动．在此基础上依据仿真结果制作了短死时间射频线圈,并应用于自主研制的低场9.51 MHz便携式NMR谱仪系统,进行NMR实验,结果显示可将收发切换时间缩短至10 μs以内,验证了该设计方案的可行性．     

基于单光子探测机理的伪随机码测距性能研究

建立了伪随机码测距的系统测距模型,从光子统计理论出发提出一种新的系统输出信噪比模型。蒙特卡罗算法模拟不同系统死时间下,系统输出信噪比和伪随机码码型的关系。理论模型与蒙特卡罗仿真基本吻合,结果表明信噪比随着伪随机码1的比例增大先增大再减小,选择最佳的发送码型可以获得最佳信噪比。根据新的模型,系统死时间的降低可提高信噪比,光子计数值增大,信噪比先增大再减小。引入系统高斯抖动,重构接收脉冲时间记录值,码速越高单点记录值出现误差的可能性越大,选取1GHz的码发送速率可完全避免距离数值误差。     

X光衍射实验的改进与校正

用X射线衍射仪做定量分析衍射实验，会出现因盖革计数器存在分辨时间而漏计的现象．为了简便地测定分辨时间，本文利用单层膜二次照射技术，导出了用来校正积分强度的近似公式，并与逐点校正法作了对比分析，二者符合很好．     

Dead time corrections to photon counting statistics II: Quantum theory

The recent formulation of the quantum theory of photodetection, based on the quantum theory of continuous measurements, is extended to the case of a (nonideal) detector which has non-zero dead time. A general result is proven which expresses the dead time modified counting statistics in terms of the counting statistics of anassociated ideal detector. As an illustration, the dead time corrections to the counting statistics of a single-mode free field are worked out, and these corrections are shown to be identical in form to the dead time corrections for a classical optical field of constant intensity.     

Estimation of key rate after setting dead time

The estimation of key rate is an important aspect of the quantum key distribution process,especially in the use of dead time.In this paper,we demonstrate a numerical simulation to estimate the average detection probability and the key rate.Using our method,the estimated average detection probability is better than the previous result.Besides,we can easily find the best dead time,especially when considering the impact of after pulse.     

A closed-form solution for removing the dead time effects from the poststimulus time histograms

Discharge patterns from cochlear nerve fibers contain important information about acoustic stimuli and encoding schemes of the peripheral auditory system. Yet these patterns are distorted due to refractory or dead time effects. By modeling discharges from peripheral auditory nerves as a self-exciting Poisson process, the effects of dead time on a poststimulus time histogram can be determined, assuming the recovery time does not depend on acoustic stimuli. If the recovery function is known, a closed-form formula is available to remove the dead time distortions from the poststimulus time histogram.     

On the effect of dead time on the counting statistical error

In X‐ray intensity measurements, the counting statistical error is typically calculated as the square root of the number of counts collected. This, however, is an approximation in the sense that the effect of the dead time in the counting process has been ignored. In this work, the equations for calculation of the counting statistical error in X‐ray fluorescence measurements will be derived, including the effect of the dead time of the counting chain. Copyright © 2016 PANalytical B.V. X‐Ray Spectrometry Published by John Wiley & Sons Ltd.     

主动抛光盘面形测试技术的研究

主动抛光盘技术是新发展起来的一种能够根据需要将抛光盘面实时地主动变形成离轴非球面来磨制深非球度高精度天文镜面的磨制技术。简单介绍了抛光盘变形控制结构和面形检测机构，对深非球面度面形变形进行了精度分析，探讨了主动抛光盘的动态响应和校正，并对抛光盘的改造提出了一些建议。     

Decaying source model: Alternative approach to determination of true counting rates at X and gamma ray counting systems

The counting systems consisting of electronic devices are used for detection of radiation due to X or gamma rays. The dead time of the counting system is based on time limitations of these electronic devices. The dead time causes counting losses. Determination of counting rate losses in quantitative and qualitative analysis become a vital step for correction of analysis. Therefore, compensating for counting rate losses is of great importance. These counting rate losses are due to piled up reject time, paralyzable or non-paralyzable system dead time or a combination of these mechanisms. Paralyzable and non-paralyzable models are well-known and frequently used for correction of counting rate losses dependent on the system dead time. However, these two models do not provide enough correction at medium and high counting rates. Therefore, the new models for corrections of counting rate losses are needed. For this reason, both an alternative approach is proposed and a simulation program is coded for counting rate losses in this study. A good agreement is obtained between theoretical model and simulation program.     

Dead time corrections to photon counting statistics I: Classical theory

A complete solution is given to the problem of calculating the dead time corrections to the counting statistics of an arbitrary doubly stochastic Poisson process with a non-negative random intensity function. It is shown that for the particular case of an optical field with constant intensity, the general dead time modified counting formula leads to a corrected version of results earlier derived by Bedard.     

用激光偏振干涉技术测量KDP晶体柱面生长速度

 采用激光偏振干涉技术实现了KDP晶体柱面生长速度的实时测量,精度可达0.01 μm/min。研究了不同的过饱和度控制方式对柱面死区实时测量的影响。发现晶体双折射率随温度的变化是导致光强-时间曲线中死区直线斜率不为零的原因。认为晶体生长速度与杂质离子的吸附时间有关。研究了杂质离子含量不同的两种原料在不同的溶液饱和点下的柱面生长速度和死区随过饱和度的变化关系,结合C-V模型和K-M理论讨论了其中的动力学规律。讨论了晶体光学质量与生长过饱和度的关系,认为利用激光偏振干涉系统进行溶液鉴定,将传统降温法的过饱和度控制在死区范围内和将点籽晶快速生长技术的过饱和度控制在线性区是保证晶体光学质量的关键。     

Dead time corrections to photocounts and clipped correlations of Gaussian light

A general method of dealing with the photocount distribution is proposed when dead time effects are to be taken into account. The clipped correlations of photocounts are investigated in detail and pointwise bounds for the correlation functions are explicitly provided when the dead times are not necessarily small compared to the sample time.