Study of time-domain digital pulse shaping algorithms for nuclear signals

With the development on high-speed integrated circuit,fast high resolution sampling ADC and digital signal processors are replacing analog shaping amplifier circuit.This paper firstly presents the numerical analysis and simulation on R-C shaping circuit model and C-R shaping circuit model.Mathematic models are established based on 1st order digital differential method and Kirchhoff Current Law in time domain,and a simulation and error evaluation experiment on an ideal digital signal are carried out with Excel VBA.A digital shaping test for a semiconductor X-ray detector in real time is also presented.Then a numerical analysis for Sallen-Key(S-K) low-pass filter circuit model is implemented based on the analysis of digital R-C and digital C-R shaping methods.By applying the 2nd order non-homogeneous differential equation,the authors implement a digital Gaussian filter model for a standard exponential-decaying signal and a nuclear pulse signal.Finally,computer simulations and experimental tests are carried out and the results show the possibility of the digital pulse processing algorithms.     

CR-RC~m滤波器数字化研究

从RC高低通滤波电路输入输出电压之间的线性常系数微分方程出发,推导出数字化CR高通和RC低通滤波器的系统传递函数,进而推导出数字化CR-RC~m成形滤波器的系统传递函数。对数字化CR-RC~m滤波器的频域特征和时域成形特征进行分析和测试,并通过实验,对数字化CR-RC~m成形滤波器滤波成形前后不同脉冲信号的能谱及能谱全能峰能量分辨率进行了测试。实验结果表明,该滤波器可对数字化的核信号成形成高斯型,使脉冲信号的上升沿变缓,峰顶变得更加平坦,提高信噪比,进而提高系统能量分辨率。     

基于实时数字脉冲处理技术的核谱仪研究

本文提出一种基于80 MHz ADC的数字化γ能谱系统。系统由探测器、前端电路、ADC和数字处理单元组成。数字处理在FPGA中完成,主要包括FIR数字滤波、脉冲梯形成形、幅度甄别、数据通讯。为减小高速ADC在采集过程中引入的噪声信号,在数字处理单元实现FIR数字滤波,对数字脉冲信号先进行滤波处理,再进行脉冲梯形成形,得到高分辨率的能谱数据。测量系统中模拟信号全部采用直流耦合,数字脉冲宽度为1.6μs,对137 Cs的能量分辨率达6.88%。     

梯形成形冲击响应函数推导、仿真和实验研究

本文介绍了利用逆 z 变换方法得到梯形成形冲击响应函数的推导过程,采用软件产生的单指数信号对其正确性进行了仿真验证。在单指数信号上加载不同标准差的高斯白噪声,经梯形成形仿真得到输出信号和输入白噪声标准差的比值约为0.447。通过搭建数字核信号获取平台,对实际输入核信号进行梯形成形,验证了推导过程与结果的正确性。     

基于S-K数字成形和种群技术的脉冲参数提取方法

核脉冲信号成形前的指数信号往往含有较为丰富的高频信号并叠加有噪音,使指数信号的参数识别变得困难,对此,本文提出一种通过成形后的信号反推成形前参数的方法。采用S-K高斯数字成形算法和种群技术,由高斯信号搜寻指数信号的参数。结果表明,该方法得到的指数脉冲参数精度高:幅值和产生时间误差在1%以内,时间常数误差为2%左右,是一种性能良好的脉冲识别方法。     

数字高斯脉冲成形算法仿真研究

高斯脉冲具有良好的时间、频率响应和较高的信噪比,探测器输出信号通常被滤波成形为高斯波形或类高斯波形。在高斯脉冲成形算法基础上,引入截止频率和品质因子,讨论成形参数对成形脉冲幅度、宽度的影响。通过与梯形脉冲成形算法对比,研究高斯脉冲成形算法的滤波效果以及对核信号幅度谱的作用。结果表明,在相同达峰时间条件下高斯脉冲成形算法具有更好的噪声抑制能力,同时可减小核信号幅度谱的半高宽;结合使用梯形脉冲成形算法可改善高斯脉冲成形算法在处理堆积脉冲中的不足,提高核信号通过率。     

基于LabVIEW的核信号数字滤波器的研制

本文介绍了基于LabVIEW的核信号数字滤波器的设计与测试。该数字滤波器实现了3种核信号的数字滤波成形方法--基于小波分析技术的高斯滤波成形、匹配滤波成形和梯形滤波成形。为验证该滤波器的性能,利用计算机产生的数字化核脉冲信号作为信号源,对各种滤波成形算法的效果进行了测试。测试结果表明,该数字滤波器的性能良好,参数调节方便,适用于对核信号进行数字滤波成形。     

Estimation method for parameters of overlapping nuclear pulse signal

Identification of nuclear pulse signal is of importance in radioactive measurements,especially in recognizing adjacent overlapping nuclear pulses.In this article,we propose an estimation method for parameters of typical overlapping nuclear pulse signals.First,the nuclear pulses are regarded as individual genes and the norm is set as the fitness function.Second,the global optimal solution is found by searching the population of genetic algorithm,so as to estimate the parameters of nuclear pulse.With high precision,this method can identify parameters of overlapping nuclear pulses in the Sallen-Key Gaussian signal decomposition experiments.This pulse recognition method is of great significance to improve the precision of radioactive measurement and is suitable for serious overlap of nuclear pluses.     

基于软核的数字化多道脉冲幅度分析器

介绍了一种数字化多道脉冲幅度分析器(DMCA),该系统采用数字梯形滤波成形等数字信号处理方法进行核脉冲信号处理,采用NOISII软核处理器进行数据处理,所有数字功能均在单片FPGA中实现。测试表明,该系统转换增益可达4 096道,最大脉冲通过率可达200 kcps以上。     

A fast, programmable, stand-alone pulse generator emulatingspectroscopy nuclear events

The design of a fast, programmable, stand-alone pulse generator emulating spectroscopy nuclear events is described. The generator is one unit in a system aiming to test the validity of the simulation and theoretical work relating to the shaping, acquisition, and processing of spectroscopy signals in different experimental situations arising from different technical and scientific fields. The generator output, which also includes piled-up shapes, can be used in many different ways. For example, it can be used: (1) as an input to a charge sensitive preamplifier and shaping amplifier system; (2) as an input to a module for real-time digital shaping of spectroscopy pulses; and (3) it can generate a digital sequence emulating a digitally sampled analog pulse. The signals that it can emulate include those from simple charge sensitive preamplifiers, from more refined analog shapers, and the signals generated directly from scintillation detectors. The main element of the generator is the Analog Devices 21060, a fast and flexible digital signal processor (DSP). This paper considers various generator configurations arising from the need to reach a compromise among generator speed, shape resolution, and memory requirements. It is possible to program both the emulated average counting rate and the time interval between two consecutive samples (tns) using a predetermined pulse shape. The minimum tns value is equal to 10 ns in parallel configurations     

实时核信号数字化脉冲成形关键技术研究

本文对理想核脉冲信号和实际探测器输出信号分别进行了计算机模拟仿真与分析,总结了不同成形时间的核脉冲信号的数字梯形成形参数的确定方法。在高计数率场合时提高了有效测量计数率,消除了部分脉冲的堆积并减少了系统死时间。同时,采用256点和512点数字三角成形方法测试了Si-PIN半导体探测器的性能,并与模拟电路成形方法进行了对比测试。测试结果表明,脉冲数字成形处理方法提高了探测器计数率和分辨率。     

High-accuracy fit of the poles of spectroscopy amplifiers designedfor mixed analog-digital filtering

In this paper, a method for the identification of the poles' and zeros' position of an analog amplifier for nuclear spectroscopy used as a prefilter for a subsequent digital filter setup is presented. The proposed technique is based upon a subspace-based system state-space identification (4SID) method, which is well suited to a data set constituted by a noisy measurement of the sampled impulse response of the circuit. The algorithm runs unassisted and does not require skills by the operator. The experiments confirm that by using the so-obtained pole values, the shape of the impulse response of the amplifier can be fit with much better than 1% accuracy. Consequently, the overall filtering (analog+digital) can have finite duration and a top with a flatness much better than 1%     

Implementation of a cusp-like for real-time digital pulse shaper in nuclear spectrometry

Pulse shaping,which improves signal-to-noise ratio excellently,has been extensively used in nuclear signal processing.This paper presents a cusp-like pulse-shaping technique developed through the recursive difference equation in time domain.It can be implemented in field programmable gate array hardware system.Another fiat-topped cusp-like shaper is developed to optimize the time constant of pulse shaping and reduce the influence of ballistic deficit.The methods of both baseline restoration and pile-up rejection are described.The 137Cs energy spectra measured with the digital cusp-like shaper are 6.6％ energy resolution,while those by traditional analog pulse shaper are 7.2％ energy resolution,under the same conditions.This technique offers flexibility,too,in adjusting the pulse shaper parameters.     

多道脉冲幅度分析中的数字基线估计方法

介绍了用于多道脉冲幅度分析的数字基线估计方法的基本特点,利用泛函变分方法推导了最小噪声基线滤波器的计权函数．利用Fourier变换导出了数字基线估计的频率响应,探讨了参数取值对其幅频特性的影响。还利用MATLAB模拟了电荷灵敏前置放大器输出的噪声电压信号,验证了最小噪声数字基线估计的处理效果。研究结果表明,数字基线估计方法能实现最佳基线估计,特别适于在数字化多道脉冲幅度分析中使用。     

数字化核能谱获取中信号处理方法的研究

介绍了将核辐射能量信号离散化后进行数字极零识别及补偿、基线扣除、低通滤波、脉冲成形和幅度分析等一系列数字化信号的处理方法，将长尾指数衰减信号成形为梯形波或三角波信号。用所述方法对实测波形进行离线处理后的结果表明，所获能谱的能量分辨率好于模拟式多道系统的测量结果。     

数字快成形算法用于慢衰减闪烁体的高计数率能谱读出

慢衰减型闪烁体(NaI(Tl)、CsI(Tl)等)探测器经过前放输出的脉冲信号具有较长的上升时间,造成电荷在收集的过程中出现严重的弹道亏损。在后续脉冲成形中为了降低弹道亏损对能量分辨率的影响,一般采用较宽的成形平顶来增加电荷的收集时间。但在高辐射粒子注量率的场合下,由于慢衰减型闪烁体输出的脉冲堆积严重,采用传统的滤波成形方式获得的脉冲计数率和能量分辨率明显降低。为解决此问题,本文提出了一种以数字反褶积为核心的数字快成形算法。该算法可去掉慢衰减型闪烁体探测系统的衰减电流拖尾,获得一理想的冲激脉冲电流,然后再通过滤波成形为一窄脉冲,并彻底消除弹道亏损的影响。通过对~(137) Csγ源测量,使用传统成形算法的能谱测量系统在成形时间为1.5μs时,其光电峰能量分辨率为6.99%,计数率为68 000s~(-1);而使用数字快成形系统,在相同情况下获得6.37%的能量分辨率,计数率可达102 000s~(-1)。因此数字快成形算法可有效地修复在高辐射粒子注量率下,窄脉冲成形引起的信号变形和拖尾,从而提高了脉冲堆积甄别能力。     

数字化多道脉冲幅度分析技术研究

多道脉冲幅度分析技术正在朝数字化方向发展,基于数字信号处理技术的数字化多道具有脉冲处理能力强、速度快、稳定性高和灵活性强等特点。文章分析了数字核脉冲处理关键技术,利用MATLAB完成了梯形成形、数字基线估计、数字极零零极补偿、极零点识别等核心算法的模拟。给出了数字化多道初步总体设计方案,探讨了工程没计中的关键技术问题,为研制国产数字化核谱仪打下了基础。     

基于数值微分核脉冲信号数字处理方法

核反应堆核测量系统测量探测器输出的核脉冲信号,该信号后沿拖尾很长,在计数率较高时容易产生信号堆积和基线漂移等问题,导致源区计数率测量上限仅能达到10⁵ Hz左右。文中基于数值微分方法,采用数字处理技术,在时域上分析了核脉冲信号经过前置放大、信号成形、低通滤波和脉冲甄别后的输出,并利用探测器实测信号进行了仿真。仿真结果表明,基于数值微分的数字处理方法可以实现相邻0.4μs脉冲信号的识别和测量,将源区测量计数率上限提升到2×10⁶ Hz以上。     

铀矿伽马能谱测井核脉冲信号数字化处理技术

在铀矿勘查中,可采用伽马能谱测井获取钻孔地层的铀、钍含量。相对于传统的模拟构架,基于数字化核脉冲信号处理技术构建的伽马能谱测井仪具有计数率高、信号噪声低和稳定性好等优点。通过采用核脉冲信号数字化处理技术,实现了伽马能谱的数字化采集,在放射性勘查模型井上进行了测试。混合模型的能谱测量铀、钍含量与标称含量的误差均小于5%,符合铀矿伽马能谱测井相关规范要求。     

剂量仪中数字滤波器设计

单探测器宽量程剂量仪测量范围能超过8个数量级,远大于常规脉冲计数法的剂量仪。在单探测器宽量程剂量仪中,平均等待时间的计算误差直接关系到最终辐射强度或剂量率的计算精度。平均时间求取的实质是采用低通滤波器处理等待时间。信号处理领域中成熟的数字滤波器设计的基础是信号频谱分析,没有考虑核探测中的随机因素,由其设计的滤波器不能同时提高响应速度与测量精度这两个指标。针对单探测器宽量程剂量仪测量等待时间与数字滤波器设计方法的特点,本文提出了基于多目标粒子群优化的滤波器设计方法。理论分析与实验结果均表明：与传统方法所设计的滤波器相比,本文方法所设计的滤波器在相同测量精度条件下具有最快的响应速度;在相同响应速度条件下,具有最高的测量精度。本方法适用于设计宽量程剂量仪或其他类型辐射测量装置的数字滤波器。