Research On The Monte Carlo Virtual Detector

Actually the nuclear pulse signal is generated by means of a detector and a radioactive source.However,in the actual situation,some detectors are so expensive that the expenditure is difficult to support the purchase.The use of radioactive sources is often limited by venues,and some radioactive sources are used for some experiments,which have a great impact for experimenter's physical health.Therefore it is necessary to find a way to generate nuclear pulse signals to replace the use of detectors and radioactive sources.In order to avoid the purchase of expensive detectors and harm of radioactive sources to the human body,this paper presents a Monte Carlo virtual detector that can simulate different types of detectors and radioactive sources.The virtual detector can simulate the physical interaction between ray and virtual detector by Monte Carlo method,thus it produces the amplitude information of nuclear pulse signal which have physical meaning.This paper firstly introduces the statistical fluctuation that appeared in the detection for the randomicity of nuclear event itself,which makes nuclear signal taking on Poisson distribution on time and Gaussian distribution on amplitude,and exponential model on the signal shape,which established the important theoretical and practical foundation to research Signal Generator of Imitated Nuclear Radiation.Then this paper introduces that the Monte Carlo virtual detectors are composed of the upper computer system and the lower computer system.In the first part,the upper computer system mainly includes Qt interface,Monte Carlo simulation and the method of Qt interface modifying,calling and running the Monte Carlo Geant4 program.It provides all kinds of detectors which users can choose,and can modify parameters of detector,radioactive,and shield.And it generates nuclear digital pulse signal and then delivery to the lower computer software by USB serial port.It also provides three kinds of time interval.Firstly,the time interval is zero.Secondly,the time interval is a constant but the constant can be set by the user.Thirdly,the time interval obey exponential distribution,in other words,the nuclear signal takes on Poisson distribution on time.In addition,it provides generator mold of some simple digital pulse signal,for example,sine and cosine digital pulse signal,square wave digital pulse signal,triangular wave digital pulse signal and so on.In the second part,the lower computer software mainly includes USB communication interface circuit,FPGA chip and its support circuit and data handling program,DAC,and low pass filter and so on.The paper takes the NaI(Tl)detector as examples to show the study of Monte Carlo virtual detector.Firstly,the paper analyzes amplitude,shape and three kinds of time interval of the nuclear pulse signal in the oscilloscope.The results of amplitude analysis show that the nuclear pulse signal amplitude,which is generated by the virtual detector,have the linear relationship with its corresponding radiation energy.Thus we can conclude that the energy spectrum which is from the Monte Carlo Simulation,obey a certain distribution and at the same time the nuclear pulse shape also obey the certain distribution.The results of shape analysis show that when the time constant is smaller,the nuclear pulse signal decline faster and its width is also smaller.In addition,their shapes meet the exponential model.The results of three kinds of time internal analysis show that the Monte Carlo virtual detector can basically realize the three kinds of time internal between the nuclear pulse signal,which represent that the time interval is zero,the time interval is a constant and the time interval obey exponential distribution.Finally,the nuclear pulse signal,which is generated by the virtual detector is used to test the performance of multichannel pulse amplitude analyzer(MCA)which is developed by my studio,in the linearity and the energy spectrum.The test results show that the MCA has good performance,thus it's concluded that the developed virtual detector has good linearity and can be used to test the linearity and the energy spectrum of MCA.In addition,the generated nuclear pulse signal amplitude not only can reflect amplitude information of the full-energy peak(Gaussian distribution),but also can reflect amplitude information of the Compton platform and backward scatting peak et al.Thus the nuclear pulse signal have the physical significance which can reflect all kinds of interaction between the ray and the matter in actual detector.