Researches Of The Digital Nuclear Timing And Analysis System On Real-time DCFD Techniques

Much of the nuclear incident time information exists in the nuclear radiation detectors output signals.For example,excited particle lifetime performance with two successive time interval distribution of the signals,Neutron energy can be expressed as the neutron flight time over the distance,the spatial location of incident particles can be expressed as time information of position sensitive detectors output signals,the type of incident particles also can be expressed in the time distribution of the signal charge.In order to detect the nature of the nuclear incident and the occurrence time and position information,we need to obtain and process nuclear pulse signal time information.Constant Fraction Timing Discriminator (CFD) is an effective timing method used to obtain particles experiment incident time in Nuclear Physics and Particle Physics.CFD triggered by a constant fraction of signals amplitude to detect the arrival time of the nuclear pulse leading edge,it is possible to correct timing accuracy in pulse amplitude fluctuations.The traditional CFD method use analog circuit to given timing signals,then use Time-to-Digital Converter (TDC) chip to quantify timing signal. Time spectral waveform of the time information through computer statistics time data.The disadvantage is analog circuit complex and system equipment is huge.Digital Constant Fraction Timing Discriminator (dCFD) is a digital timing method with using Digital Signal Processing technology to analysis nuclear pulse signals.Nuclear pulse signal quantified directly by high speed Analog-to-Digital Converters (ADC),replaced analog timing circuit by numerical simulation. Advantage of this method is using digital over-sampling keep all the nuclear incident scene information,nuclear signals amplitude,time,particle type and the other information can obtained form one measurement.System structure simpler than the analog system,the algorithm is easy to adjust for different experiment environment. According to the dCFD timing method above,a timing calculating system,which is a hardware circuit,is designed and implemented as a solution. The main technical features of the system are:using high-speed analog-digital converters convert the pulse voltage into digital signals,using MATLAB designed the appropriate filter coefficients and timing algorithm model based on the characteristic relationship between the pulse voltage and the noise voltage,using a high performance FPGA (Field Programmable Gate Array) device and a DSP (Digital Signal Processor) device parallel process of amplitude and time calculating for double-channels pulse signal.USB2.0high-speed data interface used for host communication.The innovations of this thesis are shown as follows:1、 Using MATLAB established signal noise model for dCFD offline simulation, realized Digital filter design, Optimized timing process algorithm,and developed a experiment GUI user system for online digital timing measurement, analyzed system performance, given nuclear pulse signal time histogram.2、 Designed a dCFD prototype for double-channels nuclear pulse signal measurement, based on FPGA and DSP digital processing. The mainly function of the electronics system is integrated in one NIM plug-in module, which implement real-time sampling two channel signals,filtering,incident energy calculation,incident time calculation.Presently, the prototype of electronics system has been produced. After a series of electronics test, the result show that digital electronics system prototype timing accuracy close to traditional analog electronics system, and digital System has more prominent advantages in functional integration and algorithm flexibility.