Discriminator design considerations for time-interval measurement circuits in collider detector systems

An analysis of timing jitter from leading-edge discriminators (LED's) and constant-fraction discriminators (CFD's) is presented. The jitter is calculated for the cases of random white noise, coherent noise (e.g., digital switching noise or ac power-line hum), and mixed (random and coherent) noise for both discriminator architectures. A general jitter equation valid for all of these conditions is derived. It is shown that the discriminator bandwidth for minimum jitter is strongly dependent on the amount of coherent noise. This effect is shown to be more pronounced for the LED. Even though off-line walk adjustments are possible for many timing measurements, the CFD is shown to provide a major advantage by acting as a correlated double sampler that removes much of the coherent noise expected in large, multichannel collider detector systems.     

RX64DTH -a fully integrated 64-channel ASIC for a digital X-ray imaging system with energy window selection

We report on the multichannel IC (RX64DTH) designed for position sensitive X-ray measurements with silicon strip detectors and dedicated to medical imaging applications. This integrated circuit has a binary readout architecture with a double threshold allowing on selection energy window for measured signals. The design was realized in a 0.8 /spl mu/m CMOS process. The core of the RX64DTH IC consists of 64 readout channels. The single channel is built with four basic blocks: charge sensitive preamplifier, shaper, two independent discriminators, and two independent 20-bit counters. Each readout channel counts pulses which are above the low discriminator threshold and counts pulses independently above the high discriminator threshold. The energy resolution in such architecture is limited by the noise of a single channel and by channel to channel threshold spread. We present the noise and matching performance of a 384-channel module built with a silicon strip detector and six RX64DTH ICs. In the 384-channel module an equivalent noise charge of about 200 el. rms is achieved for the shaper peaking time of 0.8 /spl mu/s and strip capacitance of 3 pF. The deviation of discriminator thresholds for the whole system is only 87 el. rms. The obtained results show that the energy resolution and uniformity of analog parameters (noise, gain, offset) are sufficient for medical diagnostic applications such as dual energy mammography and angiography.     

用于快-快定时系统的微分恒比甄别器

本文介绍了用于快-快定时系统的微分恒比甄别器。它既有定时功能,又有能量选择功能。当输入信号的上升时间为1ns、幅度从-50mV到-5V时,其时间游动是120ps。文章给出了快-快定时系统在不同动态范围的时间分辨率。当动态范围为1.4:1时,其半宽度是201ps。     

A Unique Radiation Detection Concept for a Miniature Particle Spectrometer

A three-channel particle spectrometer employing charge multiplying semiconductor detectors and tunnel diode discriminators has been constructed, environmentally tested and calibrated to detect low energy protons. The three channels have been calibrated to detect protons > 0.5 MeV, >1.5 MeV, and >45 MeV. The instrument is five orders of magnitude more sensitive to protons than to electrons above 500 KeV which ensures successful operation in the midst of electrons injected into the earth's radiation belt from the starfish experiment. The unique features of this instrument are: (1) Discriminates uniquely against a low energy photon background. (2) Electrical noise immunity due to the integration of the detector to the discriminator to give a high signal level output to the binary counter. (3) Thermally generated noise does not compete with the detected signal at the discriminator. The miniature instrument is a result of simple detection circuitry and the use of microelectronic elements in the data compressor. The data compressor consists of three binary counters having a storage capability of 218-1 bits. Each counter has a thin film network to octally encode the binary counts into an analog voltage. The counters have a 1 MHz count rate. This paper describes the instrument design and its characteristics which reflect the design constraints of the flight vehicle. The calibration of the instrument for a small half-angle cone of low energy protons from a Van De Graaff accelerator is discussed.     

A Measuring System for Studying the Time-Resolution Capabilities of Fast Photomultipliers

A measuring system has been developed for studying and optimizing the time-resolution capabilities of fast photoelectric devices, such as standard and microchannel type photomultipliers. The system incorporates a subnanosecond light-pulse generator capable of operating at repetition frequencies up to 3 MHz with output light pulses having a full width at half-maximum of less than 200 psec, and a zero-crossing discriminator which has a time walk of ±40 psec over a 170 mV to 8 V input-pulse amplitude variation. Averaging the data from several successive measurements, the measuring system time resolution is 20 psec.     

简单的n、γ分辨系统

本文介绍了一种简单的n、γ分辨系统和适用于该系统的探测器和脉冲形状甄别器,给出了系统参数、等效电子能量与n、γ分辨特性的关系,以及在~(241)Am-Be源、2.5MeV中子束和14MeV中子束情况下的n、γ时间分布。     

A Pulse Processor for X-Ray Spectrometry with Si(Li)-Detectors

This paper describes the general features of a pulse processor for use with opto-electronic charge sensitive head amplifiers particularly with Si(Li) X-ray detectors. The instrument contains time-variant filters with direct coupled amplifiers and comprehensive pile-up protection and live time correction. The test results indicate that the system can cope with extremely wide range of signal processing times, counting rates and changes of spectral content without any appreciable degradation in energy resolution and with useful output rates for input rates up to well over 50,000 events/sec.     

Timing Electronics and Fast Timing Methods with Scintillation Detectors

Time spectroscopy involves the measurement of the time relationship between two events. This paper reviews time pick-off techniques, practival time-pickoff circuits, and timing with scintillation detectors. A detailed comparison is made between leading-edge timing and constant-fraction timing. Typical timing resolution results are given for 60Co.     

蒸汽发生器水位双PI控制的改进研究

蒸汽发生器（SG）水位的控制问题是压水堆核电站紧急停堆的1个重要原因,尤其在低功率情况下,缩胀效应致使水位控制较难。为了避开水位变化初期的假水位的影响,在控制过程中加入判别器来决定水位信号是否参与控制。采用遗传算法对控制器参数进行整定,采用的SG水位模型是简化的数学模型。对控制器中有无判别器的控制效果进行了对比。对比结果表明：加入判别器后,缩短了调节时间,降低了超调量。     

A real-time neutron-gamma discriminator based on the support vector machine method for the time-of-fiight neutron spectrometer

A new neutron-gamma discriminator based on the support vector machine (SVM) method is proposed to improve the performance of the time-of-fiight neutron spectrometer. The neutron detector is an EJ-299-33 plastic scintillator with pulse-shape discrimination (PSD) property. The SVM algorithm is implemented in field programmable gate array (FPGA) to carry out the real-time sifting of neutrons in neutron-gamma mixed radiation fields. This study compares the ability of the pulse gradient analysis method and the SVM method. The results show that this SVM discriminator can provide a better discrimination accuracy of 99.1%. The accuracy and performance of the SVM discriminator based on FPGA have been evaluated in the experiments. It can get a figure of merit of 1.30.     

A real-time neutron-gamma discriminator based on the support vector machine method for the time-of-flight neutron spectrometer

A new neutron-gamma discriminator based on the support vector machine(SVM) method is proposed to improve the performance of the time-of-flight neutron spectrometer. The neutron detector is an EJ-299-33 plastic scintillator with pulse-shape discrimination(PSD) property. The SVM algorithm is implemented in field programmable gate array(FPGA) to carry out the real-time sifting of neutrons in neutron-gamma mixed radiation fields. This study compares the ability of the pulse gradient analysis method and the SVM method. The results show that this SVM discriminator can provide a better discrimination accuracy of 99.1%. The accuracy and performance of the SVM discriminator based on FPGA have been evaluated in the experiments. It can get a figure of merit of 1.30.     

Active control of noise amplification in the flow over a square leading-edge flat plate utilizing DBD plasma actuator

Perturbation is generally considered as the flow noise,and its energy can gain transient growth in the separation bubble.The amplified perturbations may cause unstable Kelvin–Helmohltz vortices which induce the three-dimensional transition.Active control of noise amplification via dielectric barrier discharge plasma actuator in the flow over a square leading-edge flat plate is numerically studied.The actuator is installed near the plate leading-edge where the separation bubble is formed.The maximum energy amplification of perturbations is positively correlated with the separation bubble scale which decreases with the increasing control parameters.As the magnitude of noise amplification is reduced,the laminar-turbulent transition is successfully suppressed.     

Analog rise-time discriminator for CdZnTe detector

Due to variable time for charge collection,energy resolution of nuclear detectors declines,especially compound semiconductor detectors like cadmium zinc telluride (CdZnTe) detector.To solve this problem,an analog rise-time discriminator based on charge comparison principle is designed.The reference charge signal after attenuation is compared with the deconvoluted and delayed current signal.It is found that the amplitude of delayed current signal is higher than that of the reference charge signal when rise time of the input signal is shorter than the discrimination time,thus generating gating signal and triggering DMCA (digital multi-channel analyzer) to receive the total integral charge signal.When rise time of the input signal is longer than discrimination time,DMCA remains inactivated and the corresponding total integral charge signal is abandoned.Test results show that combination of the designed rise-time discriminator and DMCA can reduce hole tailing of CdZnTe detector significantly.Energy resolution of the system is 0.98％@662 keV,and it is still excellent under high counting rates.     

Energy-dependent systematic errors in dual-energy X-ray CT

Dual-energy X-ray computed tomography (DECT) is a technique which is designed to allow the determination of energy-independent material properties. In this study, results of a computer simulation show that energy-dependent systematic errors exist in the values of attenuation coefficients synthesized using the basis material decomposition technique with acrylic and aluminum as the basis materials, especially when a high atomic number element such as iodine (e.g., from radiographic contrast media) is present in the body. The errors are reduced when an acrylic and an iodine-water mixture are used as the basis materials. The authors propose a simple theoretical model for the calculation of energy-dependent systematic errors using effective energies at the lower and higher energy windows of the X-ray spectrum used in the DECT system. The calculated errors agree well with the errors observed in the simulation. These results suggest that the observed systematic errors are predominantly due to the energy dependence of the basis material coefficients     

Determination of Charge Sensitivity of a Tunnel Diode Voltage Threshold Discriminator Used in Time Difference Measurements

The results of an investigation of the delay time variation of a tunnel diode (TD) threshold sensing discriminator are presented. These variations are a function of the square root of the input signal risetime and are accountable in terms of a charge sensitivity of the tunnel diode. A distinction is made between the charge sensitivity due to continuously rising signals and that due to short low energy pulses. A simple experimental method used for measuring the delay time variation as a function of the input signal risetime is described. The method is quite general and may be applied to any type of threshold discriminator. A theoretical model of the tunnel diode operating in the discriminator mode is developed. An equivalent circuit approach is used in this development by considering three phases of operation; before the TD reaches threshold, during the actual TD switching, and after the TD has fired. The model agrees with the experimental data, and it is concluded that the charge sensitivity model is a usefully valid concept which is applicable to the design and prediction of discriminator time-delay characteristics.     

基于波形采样的PPAC数据处理

数字化波形采样技术在实验核物理中得到了广泛的应用,选取合适的采样频率非常重要。本文使用脉冲幅度甄别定时方法和恒比定时方法对采样频率为100 MHz~5 GHz的平行板雪崩计数器(PPAC)信号进行了模拟分析,采样频率为250~500 MHz时,使用脉冲幅度甄别定时方法可得到比较精确的位置信息,与传统获取系统定位的位置分辨的差别Sigma小于0.15 mm,采样频率低于100 MHz时信号定位误差较大。使用高速采样数字化仪可对信号幅度小于20 mV的信号进行定时分析,与传统的PPAC获取系统相比,探测效率提升了4.3%。     

上升时间法的α/γ波形数字化实时甄别

基于CsI(Tl)探测器的α/γ波形甄别能力,采用上升时间法,设计了一种波形实时甄别系统,系统由高速ADC和高性能FPGA组成。介绍了实时甄别系统的方案设计和甄别算法设计,利用60 Coγ源、241 Amα源对实时系统进行了甄别测试。研究表明:设计的数字化实时波形甄别系统体积小,能实时甄别开α、γ粒子,甄别品质因子为0.687 5,事件计数率可达2.5×105 s-1。     

一个分辨时间小于3ns的快甄别-快计数系统

本文叙述一个快甄别-快计数电路的设计和结果。快甄别电路由高速砷化镓隧道二极管组成,快计数电路由ECL超高速D触发器组成。此系统的分辨时间小于3ns,甄别阈范围为10mV至400mV。     

一种简便的快速定时甄别电路

介绍了一种快速定时甄别器的电路实现。输入可以是各种电平的正相或者负相信号,输出是多路脉冲宽度可调的负相标准NIM信号。这个电路具有较好的定时精度和极小的输出延时,输出脉冲宽度可调,一直在量子信息实验中稳定使用。