CN118041461A - Nuclear radiation detection signal real-time digital simulation system and method - Google Patents
Nuclear radiation detection signal real-time digital simulation system and method Download PDFInfo
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Abstract
The invention discloses a real-time digital simulation system and method for nuclear radiation detection signals, which mainly solve the problems of poor application flexibility and real-time performance of the existing simulation equipment. The simulation system comprises an upper computer, a pulse signal forming module connected with the upper computer through a communication module, a nuclear signal sequence generating module connected with the pulse signal forming module, a spectral line distribution simulation calculation module connected with the nuclear signal sequence generating module, a random number generating module connected with the spectral line distribution simulation calculation module, and a DAC output module connected with the pulse signal forming module. According to the invention, the particle transport process is simulated by arranging the radiation source, the detector, the physical process and the detection environment information, and the nuclear pulse signal is generated, so that the particle transport system has stronger flexibility. The simulation method of the invention allows the nuclear event information to be calculated and sent into the FIFO, and simultaneously takes out the signals stored in the queue before to be output, so that the time expenditure is not needed, and the timeliness is higher.
Description
Technical Field
The invention belongs to the technical field of nuclear radiation detection, and particularly relates to a system and a method for real-time digital simulation of nuclear radiation detection signals.
Background
In the fields of nuclear physics experiments and radiation detection, the use of nuclear pulse generators is of paramount importance. These devices are used to simulate real radiation detection signals, allowing an operator to calibrate and test nuclear instruments in a controlled environment without a radioactive source. In particular, for detection by gamma-ray spectrometers, X-ray fluorescence analyzers, and the like, such analog techniques play a critical role in generating accurate pulse signal waveforms and energy deposition spectral distributions.
The implementation of a conventional nuclear signal generator involves several key elements. First is to simulate a typical pulse from a radiation detector, including pulses having exponentially rising and falling shapes. The generation of these pulses may be based on an RC circuit or digitally synthesized by using a high speed DAC controlled by an FPGA. Furthermore, it is important to adjust the amplitude of the pulses to simulate the different energy deposition generated by the radiation within the detector, while the control of the pulse rate is used to simulate the rate of change of the interaction of the radiation with the detector. Advanced pulse generators also incorporate controlled noise into the signal in order to increase the realism of the analogue signal. In addition, the nuclear signal generator must also be designed to take into account pre-storage and sampling of the energy spectrum distribution to determine specific parameters of the pulse signal. However, the spectral distribution data needs to be obtained by pre-storing measured data or using monte carlo simulation software, which may affect the flexibility and real-time of the application of the device.
The limitations of the above technology indicate that there is a need for a generating system that can simulate real radiation detection processes in real time and dynamically generate nuclear pulse signals. Such a system should be capable of calculating particle transport processes in real time to generate pulse sequences with similar statistical characteristics to real nuclear events while dynamically generating pulse waveforms that meet the specified type of detector resolution and electronic system characteristics. The design and implementation of such a method and system would be highly advantageous for improving the convenience and safety of nuclear radiation detection experiments.
Disclosure of Invention
The invention aims to provide a system and a method for real-time digital simulation of nuclear radiation detection signals, which mainly solve the problems of poor application flexibility and poor real-time performance of the existing simulation equipment.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
The real-time digital simulation system for the nuclear radiation detection signals comprises an upper computer, a pulse signal forming module, a nuclear signal sequence generation module, a spectral line distribution simulation calculation module, a random number generation module and a DAC output module, wherein the pulse signal forming module is connected with the upper computer through a communication module; the spectral line distribution simulation calculation module is also connected with the communication module.
Further, in the invention, the pulse signal forming module comprises a front-end circuit structure information module, a front discharge circuit transfer function module, a pulse waveform recursion calculation module and a pulse shaper which are connected in sequence; the input end of the front-end circuit structure information module is connected with the communication module, the other input end of the pulse shaper is connected with the nuclear signal sequence generation module, and the output end of the pulse shaper is connected with the DAC output module.
Further, in the present invention, the core signal sequence generating module includes two core event sequence modules, a pulse interval module connected to both the two core event sequence modules, and an energy spectrum widening module connected to the pulse interval module; the input ends of the two nuclear event sequence modules and the energy spectrum widening module are connected with the spectral line distribution simulation calculation module, and the output end of the energy spectrum widening module is connected with the pulse shaper.
Further, in the invention, the spectral line distribution simulation calculation module comprises a detector information acquisition module, a radioactive source information acquisition module, a geometric model acquisition module, a material list acquisition module and a physical process acquisition module which are directly arranged through an upper computer; the energy deposition event real-time Monte Carlo simulation module is connected with the geometric model acquisition module, the material list acquisition module and the physical process acquisition module; the geometrical model acquisition module is also connected with the detector information acquisition module, and the physical process acquisition module is also connected with the radioactive source information acquisition module; the energy deposition event real-time Monte Carlo simulation module is connected with the two nuclear event sequence modules, and the detector information acquisition module is connected with the energy spectrum widening module.
Further, in the invention, the random number generation module adopts an LFSR random number generator which is connected with the energy deposition event real-time Monte Carlo simulation module, the pulse interval module and the energy spectrum widening module.
Further, in the invention, the DAC output module comprises a DAC controller connected with the pulse shaper and a multipath filtering output circuit connected with the DAC controller; the filtering output circuit consists of a DAC (digital-to-analog converter) and a filtering and amplifying circuit which are connected; the DAC is connected with the DAC controller, and the filtering and amplifying circuit is connected to the device to be tested.
Further, the invention also comprises a signal mixing module arranged between the pulse signal shaping module and the DAC output module; the signal mixing module comprises three signal mixing modules, a digital baseline module, a digital noise module, an adjustable digital filter and an ADC; the signal output by the pulse signal forming module is mixed with the signal output by the digital baseline module in a first signal mixing module, the signal output by the first signal mixing module is mixed with the signal output by the digital noise module in a second signal mixing module, the external input signal is mixed with the signal output by the second signal mixing module in a third signal mixing module after ADC conversion, and the third signal mixing module outputs the mixed signal to the DAC controller; the signal of the digital noise module is converted into a Gaussian white noise sequence by the output sequence of the LFSR random number generator and is sent to the adjustable digital filter module to obtain the signal.
Based on the simulation system, the invention also provides a real-time digital simulation method of the nuclear radiation detection signal, which comprises the following steps:
s1, setting a radiation detection environment model to be simulated, a detector for outputting a signal and front-end circuit information through an upper computer; the set information is converted into a differential equation with high digital system through a front discharge circuit transfer function module, and algorithm parameter setting of the pulse shaper is obtained;
s2, calculating each particle transport process in real time by utilizing a spectral line distribution simulation calculation module to obtain the energy deposited in a detection area;
S3, sampling by using a nuclear signal sequence generating module to obtain time interval and spectrum broadening information of a nuclear event, sending the obtained single nuclear event information into a FIFO (first in first out) queue in the nuclear signal sequence generating module, and taking out elements from the queue to carry out pulse waveform output by a pulse shaper after parameter setting;
s4, mixing a base line, noise and an external input signal into a pulse waveform output by the pulse shaper and sending the mixed signal to the DAC output module;
S5, the DAC output module outputs pulse sequence signals with the amplitude, time distribution, waveform and noise characteristics being simulated and controllable.
Further, in the real-time calculation of step S2, if the integral of the distribution of the given characteristics of the incident particles over the interval [ a, b ] in the specified calculation region is C and the probability density function is f (x), then:
Wherein N i >0 is a constant, 0.ltoreq.g i (x).ltoreq.1, and f i (x) is a normalized probability density function over the interval [ a, b ], then taking g i (x) as a criterion, sampling f i (x) can be constructed to realize analog sampling of f (x); the particles at a given position in space will pass a certain distance in the medium until the next event occurs, and their mean free path is:
Wherein N is the type of substances in the medium, N i is the proportion of the ith substance in the medium, and sigma (Z i, E) is the total differential reaction cross section of the material corresponding to the substance; for a segment with multiple medium paths, the number of the particles passing through the mean free path is n λ, and if n r is the number of the particles passing through the mean free path from the starting point to the position of the nuclear event, the distribution is that Let ζ be a random variable obeying a uniform distribution over the interval (0, 1), then:
The method is characterized in that the average free path number from the starting point to the position where the nuclear event occurs is sampled, so that the track length delta x of the particle with one-time action can be obtained, and the simulation of the particle transportation process is realized.
Further, in the pulse shaper output pulse waveform of step S3, a transfer function of a system formed by the detector and the preamplifier is:
Wherein p k is the pole of the analog system, and the pole is obtained after digitizing by taking T as the sampling period:
The method can be used for obtaining after finishing:
wherein P k and Z l are respectively poles and zeros of the digital system, and r is a constant, and a differential equation of the output signal is written:
Where x (T) is an input signal sequence with T as a sampling period, and y (T) is a desired pulse waveform signal.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, the particle transport process is simulated by arranging the radiation source, the detector, the physical process and the detection environment information, and the nuclear pulse signal is generated, so that the particle transport system has stronger flexibility.
(2) The simulation method of the invention allows the nuclear event information to be calculated and sent into the FIFO, and simultaneously, the signals stored in the queue previously are taken out for output, so that the time expenditure is not needed, and the timeliness is higher.
(3) The invention accords with the statistical characteristics of the actual measurement process through the change rule of the distribution characteristics such as spectral line resolution and the like generated by real-time simulation along with time, the traditional nuclear signal generator for sampling from the pre-stored spectral line does not have the capability, the signal waveform is calculated in real time through a differential equation derived from a system transfer function, and the physical significance is clearer.
(4) The energy spectrum and the pulse can be dynamically generated, and the problems that the traditional nuclear signal generator needs to simulate or actually measure energy spectrum data in advance and sample the energy spectrum data, the preparation work in the early stage is complicated, and the pre-stored energy spectrum and pulse waveform are limited are effectively solved.
(5) The invention allows an operator to calibrate and test nuclear instrumentation in a radiation-free environment using known controllable signal sources with convenience and safety.
(6) The simulation system of the present invention has a plurality of signal output channels, can simulate time-dependent signals, can be used for testing in accordance with a measuring instrument, and has a function of mixing an external signal source, such as mixing known noise or signals into output signals of other detectors, and is used for debugging a pulse amplitude analyzer in more cases, etc.
Drawings
FIG. 1 is a block diagram of the system of the present invention;
FIG. 2 simulates a core signal generation flow diagram;
FIG. 3 illustrates an example detector analog front end equivalent circuit diagram;
FIG. 4 illustrates a diagram of a geometric model of a nuclear radiation detection system;
Fig. 5 is a graph of the generated analog signal and the measured signal.
Detailed Description
The invention will be further illustrated by the following description and examples, which include but are not limited to the following examples.
As shown in fig. 1, the invention discloses a real-time digital simulation system for nuclear radiation detection signals, which comprises an upper computer, a pulse signal forming module connected with the upper computer through a communication module, a nuclear signal sequence generating module connected with the pulse signal forming module, a spectral line distribution simulation calculation module connected with the nuclear signal sequence generating module, a random number generating module connected with the spectral line distribution simulation calculation module, and a DAC output module connected with the pulse signal forming module; the spectral line distribution simulation calculation module is also connected with the communication module.
In this embodiment, the pulse signal forming module includes a front end circuit structure information module, a front discharge circuit transfer function module, a pulse waveform recurrence calculation module, and a pulse shaper, which are sequentially connected; the input end of the front-end circuit structure information module is connected with the communication module, the other input end of the pulse shaper is connected with the nuclear signal sequence generation module, and the output end of the pulse shaper is connected with the DAC output module. The generation of the signal waveform is performed in a digital system, and the transfer function of the system consisting of the detector and the preamplifier can be written as:
Wherein p k is the pole of the analog system, and the pole is obtained after digitizing by taking T as the sampling period:
The method can be used for obtaining after finishing:
Wherein P k and Z l are respectively poles and zeros of the digital system, and r is a constant, and a differential equation of the output signal can be written:
Where x (T) is an input signal sequence with T as a sampling period, and y (T) is a desired pulse waveform signal.
In this embodiment, the core signal sequence generating module includes two core event sequence modules, a pulse interval module connected to both the two core event sequence modules, and a spectrum widening module connected to the pulse interval module; the input ends of the two nuclear event sequence modules and the energy spectrum widening module are connected with the spectral line distribution simulation calculation module, and the output end of the energy spectrum widening module is connected with the pulse shaper. The module sends single core event information obtained by calculating the detection area each time to the FIFO queue, and takes out elements from the queue to be substituted into the pulse shaping module to output pulse waveforms. Wherein the nuclear event contains pulse amplitude and particle type information subject to an energy spectrum distribution and is sampled from a particular distribution to obtain time interval information related to the activity of the source and spectral broadening information related to the energy resolution of the detector.
In this embodiment, the spectral line distribution simulation calculation module includes a detector information acquisition module, a radioactive source information acquisition module, a geometric model acquisition module, a material list acquisition module and a physical process acquisition module, which are directly set by an upper computer; the energy deposition event real-time Monte Carlo simulation module is connected with the geometric model acquisition module, the material list acquisition module and the physical process acquisition module; the geometrical model acquisition module is also connected with the detector information acquisition module, and the physical process acquisition module is also connected with the radioactive source information acquisition module; the energy deposition event real-time Monte Carlo simulation module is connected with the two nuclear event sequence modules, and the detector information acquisition module is connected with the energy spectrum widening module. The module plays a role after the basic communication module transmits the information of the radiation detection model to be simulated into the spectral line distribution simulation calculation module, and the required information comprises detector information, radioactive source information, a geometric model of a detection environment, a material list corresponding to each object and a physical process to be considered. If the integral of the distribution of given features of the incident particle over the interval [ a, b ] in a given calculation region is C, the probability density function is f (x), it can be written as:
Where N i >0 is a constant, 0.ltoreq.g i (x). Ltoreq.1, and f i (x) is a normalized probability density function over the interval [ a, b ], then taking g i (x) as a criterion, sampling f i (x) can be implemented by sampling f (x) with a suitable construction. The particles at a given position in space will pass a certain distance in the medium until the next event occurs, and their mean free path is:
Wherein N is the type of substance in the medium, N i is the proportion of the ith substance in the medium, and sigma (Z i, E) is the total differential reaction cross section of the material corresponding to the substance. For a segment with multiple medium paths, the number of the particles passing through the mean free path is n λ, and if n r is the number of the particles passing through the mean free path from the starting point to the position of the nuclear event, the distribution is that Let ζ be a random variable obeying a uniform distribution over the interval (0, 1), then:
The method is characterized in that the average free path number from the starting point to the position where the nuclear event occurs is sampled, so that the track length delta x of the particle with one-time action can be obtained, and the simulation of the particle transportation process is realized.
In this embodiment, the random number generation module employs an LFSR random number generator, and the LFSR random number generator is connected to the energy deposition event real-time monte carlo simulation module, the pulse interval module, and the energy spectrum widening module. The recurrence relation of the n-stage LFSR output is:
an+k＝cn·an+k-1+cn-1·an+k-2+…+c1·ak
Where a n+k is the state of the nth bit binary register in the kth recursive computation, c n is the feedback coefficient of the nth stage, and both the addition and multiplication are modulo-2 operations. Let the constant coefficient be the coefficient of the primitive polynomial, the linear recurrence sequence can obtain a sequence with period of 2 n -1. The FPGA can then generate a 1-bit binary pseudo-random number per clock cycle. Since FPGA is suitable for parallel computing, to increase efficiency, a multi-bit pseudorandom number can be generated in one clock cycle, letting:
Ak+m＝CmAk
Wherein A is a binary sequence with length of n, C is an n-order feedback coefficient matrix, if m is less than or equal to n, then C m is used as a feedback network to obtain an m-bit pseudo-random number in one clock period, and the initial value of the pseudo-random number is A 0 and can be any n-bit binary number which is not 0. The random number generated by the method has long cycle period and higher quality.
In this embodiment, the DAC output module includes a DAC controller connected to the pulse shaper, and a multiplexing output circuit connected to the DAC controller; the filtering output circuit consists of a DAC (digital-to-analog converter) and a filtering and amplifying circuit which are connected; the DAC is connected with the DAC controller, and the filtering and amplifying circuit is connected to the device to be tested. The output signal of the DAC is regulated to the range of the required amplitude and bandwidth by the filtering amplifying circuit, and finally the amplitude and time distribution and the waveform and noise characteristics are highly similar to those of the real radiation detection signal, so that the known and controllable pulse sequence signal is sent to the equipment to be tested. The system and the method are used for simulating real nuclear radiation detection signals in real time, allow an operator to calibrate and test a nuclear instrument in a controlled environment without a radioactive source, and play an important role in the fields of nuclear physical experiments and radiation detection.
The embodiment also comprises a signal mixing module arranged between the pulse signal forming module and the DAC output module; the signal mixing module comprises three signal mixing modules, a digital baseline module, a digital noise module, an adjustable digital filter and an ADC; the signal output by the pulse signal forming module is mixed with the signal output by the digital baseline module in a first signal mixing module, the signal output by the first signal mixing module is mixed with the signal output by the digital noise module in a second signal mixing module, the external input signal is mixed with the signal output by the second signal mixing module in a third signal mixing module after ADC conversion, and the third signal mixing module outputs the mixed signal to the DAC controller; the signal of the digital noise module is converted into a Gaussian white noise sequence by the output sequence of the LFSR random number generator and is sent to the adjustable digital filter module to obtain the signal. The base line and noise signals are mixed in the signals, the noise signals are converted into Gaussian white noise sequences by the output sequence of the random number generator and sent to the adjustable digital filter module to obtain the analog signal simulation device, the analog signal simulation device can be used for simulating thermal noise, shot noise, 1/f noise and the like in a required bandwidth range, external input signals can be further mixed in the output signals, so that the flexibility of system use is improved, the application range of the system is expanded, and the digital signals obtained through the series of processes are further sent to the DAC control module so as to realize analog signal output.
As shown in fig. 2, based on the above simulation system, the present embodiment further provides a method for real-time digital simulation of a nuclear radiation detection signal, which includes the following steps:
s1, setting a radiation detection environment model to be simulated, a detector for outputting a signal and front-end circuit information through an upper computer; the set information is converted into a differential equation with high digital system through a front discharge circuit transfer function module, and algorithm parameter setting of the pulse shaper is obtained;
s2, calculating each particle transport process in real time by utilizing a spectral line distribution simulation calculation module to obtain the energy deposited in a detection area;
S3, sampling by using a nuclear signal sequence generating module to obtain time interval and spectrum broadening information of a nuclear event, sending the obtained single nuclear event information into a FIFO (first in first out) queue in the nuclear signal sequence generating module, and taking out elements from the queue to carry out pulse waveform output by a pulse shaper after parameter setting;
s4, mixing a base line, noise and an external input signal into a pulse waveform output by the pulse shaper and sending the mixed signal to the DAC output module;
S5, the DAC output module outputs pulse sequence signals with the amplitude, time distribution, waveform and noise characteristics being simulated and controllable.
Take the analog front end equivalent circuit as shown in fig. 3 as an example. R D is the load resistance of the detector, C i is the input capacitance of the amplifier, C f is the feedback capacitance, connected in parallel with resistor R f. The system transfer function is obtained according to the set radiation detector information and the type and structure of a pre-amplifying circuit and the like of the nuclear power system analog front end, and is as follows:
the transfer function of the analog system is converted into a differential equation of the digital system through calculation, so that algorithm parameter setting of the pulse shaper module is obtained, and signals output by the pulse shaper module are as follows:
The energy and time information of the nuclear event is contained, wherein Q is the amount of charge deposited in the detector, and the amount of charge needs to be obtained from a spectral line distribution simulation calculation module.
And calculating the particle transport process in real time according to the set ray source, the geometric model and the physical process in the spectral line distribution simulation calculation module to obtain the energy deposited in the detection area. The geometric model of an exemplary nuclear radiation detection system and a portion of the calculated particle trajectories are shown in fig. 4. The detector is made of NaI, a layer of Fe shell is wrapped, the radioactive source is a gamma ray point source, and the gamma ray point source and the detector are placed in a lead chamber together. The inner measuring cylinder is a detector and a shell, the outer hollow cylinder is a lead chamber, the space inside the lead chamber is filled with air, and the outside is vacuum. The ray source is gamma photon with energy of 0.661MeV, and the physical process of the interaction of the ray and the substance mainly considers the photoelectric effect, compton effect and electron pair effect, and does not consider the characteristic X-ray and Auger electron effect generated by the retrograde excitation of 137 Cs decay daughter.
The nuclear event obtained by sampling the ray source each time contains pulse amplitude and particle type information obeying energy spectrum distribution, and the time interval and line broadening information are obtained by sampling from specific distribution. The random variables which are uniformly distributed by the random number generation module can be obtained by an inverse function direct sampling method, and the random variables obeying the exponential distribution are obtained by the inverse function direct sampling method, and the exponential distribution function is as follows:
Then:
I.e. random variables obeying an exponential distribution, where ζ is random variable obeying a uniform distribution over the interval (0, 1), resulting in a time interval for the event. After obtaining the random variable of the exponential distribution, a random variable which is compliant with the normal distribution can be obtained by using a selective sampling method. The probability density function of the standard normal distribution is:
Can be configured as follows:
The h (x) is taken as a criterion to sample from the distribution with the probability density function of g (x) to obtain the distribution of f (x), the sampling efficiency of the random variable which is compliant with normal distribution is 1/M, and the Gaussian distribution of line broadening can be obtained by combining the resolution information of the detector, and the pulse amplitude of the incident is sampled.
And sending the single core event information obtained by each calculation into a FIFO (first in first out) queue, taking out corresponding information from the queue according to a sampling rate, inputting the information into a pulse forming module, outputting a pulse waveform, further mixing a base line and noise into the signal, sending the signal into a DAC (digital-to-analog converter) control module, and outputting a pulse sequence signal with amplitude, time distribution, waveform and noise characteristics which are both simulated and controllable. A comparison of the instrument spectrum obtained by actually detecting the 137 Cs source in the lead chamber using a NaI scintillation detector with the radiation detection spectrum simulated using the method of the present invention is shown in fig. 5. It can be seen that the system and method for real-time digital simulation of nuclear radiation detection signals of the present invention can generate analog signals highly similar to the measured energy spectrum, and can be used to simulate real radiation detection signals, and can also be used to calibrate or test nuclear instruments without a radioactive source.
Through the design, the particle transport process is simulated by arranging the radioactive source, the detector, the physical process and the detection environment information, and the nuclear pulse signal is generated, so that the particle transport system has stronger flexibility. The simulation method of the invention allows the nuclear event information to be calculated and sent into the FIFO, and simultaneously takes out the signals stored in the queue before to be output, so that the time expenditure is not needed, and the timeliness is higher.
The above embodiment is only one of the preferred embodiments of the present invention, and should not be used to limit the scope of the present invention, but all the insubstantial modifications or color changes made in the main design concept and spirit of the present invention are still consistent with the present invention, and all the technical problems to be solved are included in the scope of the present invention.
Claims (10)
1. The real-time digital simulation system for the nuclear radiation detection signals is characterized by comprising an upper computer, a pulse signal forming module, a nuclear signal sequence generating module, a spectral line distribution simulation calculating module, a random number generating module and a DAC output module, wherein the pulse signal forming module is connected with the upper computer through a communication module; the spectral line distribution simulation calculation module is also connected with the communication module.
2. The system according to claim 1, wherein the pulse signal shaping module comprises a front-end circuit structure information module, a front-end circuit transfer function module, a pulse waveform recurrence calculation module and a pulse shaper which are sequentially connected; the input end of the front-end circuit structure information module is connected with the communication module, the other input end of the pulse shaper is connected with the nuclear signal sequence generation module, and the output end of the pulse shaper is connected with the DAC output module.
3. The system of claim 2, wherein the nuclear signal sequence generation module comprises two nuclear event sequence modules, a pulse interval module connected to both of the two nuclear event sequence modules, and a spectrum broadening module connected to the pulse interval module; the input ends of the two nuclear event sequence modules and the energy spectrum widening module are connected with the spectral line distribution simulation calculation module, and the output end of the energy spectrum widening module is connected with the pulse shaper.
4. A real-time digital simulation system of nuclear radiation detection signals according to claim 3, wherein the spectral line distribution simulation calculation module comprises a detector information acquisition module, a radioactive source information acquisition module, a geometric model acquisition module, a material list acquisition module and a physical process acquisition module which are directly arranged by an upper computer; the energy deposition event real-time Monte Carlo simulation module is connected with the geometric model acquisition module, the material list acquisition module and the physical process acquisition module; the geometrical model acquisition module is also connected with the detector information acquisition module, and the physical process acquisition module is also connected with the radioactive source information acquisition module; the energy deposition event real-time Monte Carlo simulation module is connected with the two nuclear event sequence modules, and the detector information acquisition module is connected with the energy spectrum widening module.
5. The system of claim 4, wherein the random number generation module is an LFSR random number generator, and the LFSR random number generator is connected to the energy deposition event real-time monte carlo simulation module, the pulse interval module, and the energy spectrum widening module.
6. The system of claim 5, wherein the DAC output module comprises a DAC controller coupled to the pulse shaper and a multiplexing output circuit coupled to the DAC controller; the filtering output circuit consists of a DAC (digital-to-analog converter) and a filtering and amplifying circuit which are connected; the DAC is connected with the DAC controller, and the filtering and amplifying circuit is connected to the device to be tested.
7. The system of claim 6, further comprising a signal mixing module disposed between the pulse signal shaping module and the DAC output module; the signal mixing module comprises three signal mixing modules, a digital baseline module, a digital noise module, an adjustable digital filter and an ADC; the signal output by the pulse signal forming module is mixed with the signal output by the digital baseline module in a first signal mixing module, the signal output by the first signal mixing module is mixed with the signal output by the digital noise module in a second signal mixing module, the external input signal is mixed with the signal output by the second signal mixing module in a third signal mixing module after ADC conversion, and the third signal mixing module outputs the mixed signal to the DAC controller; the signal of the digital noise module is converted into a Gaussian white noise sequence by the output sequence of the LFSR random number generator and is sent to the adjustable digital filter module to obtain the signal.
8. A method for real-time digital simulation of nuclear radiation detection signals, characterized in that an analog system according to any one of claims 1 to 7 is used, comprising the following steps:
s1, setting a radiation detection environment model to be simulated, a detector for outputting a signal and front-end circuit information through an upper computer; the set information is converted into a differential equation with high digital system through a front discharge circuit transfer function module, and algorithm parameter setting of the pulse shaper is obtained;
s2, calculating each particle transport process in real time by utilizing a spectral line distribution simulation calculation module to obtain the energy deposited in a detection area;
S3, sampling by using a nuclear signal sequence generating module to obtain time interval and spectrum broadening information of a nuclear event, sending the obtained single nuclear event information into a FIFO (first in first out) queue in the nuclear signal sequence generating module, and taking out elements from the queue to carry out pulse waveform output by a pulse shaper after parameter setting;
s4, mixing a base line, noise and an external input signal into a pulse waveform output by the pulse shaper and sending the mixed signal to the DAC output module;
S5, the DAC output module outputs pulse sequence signals with the amplitude, time distribution, waveform and noise characteristics being simulated and controllable.
9. The method according to claim 8, wherein during each particle transport process of the real-time calculation in step S2, if the integral of the distribution of the given characteristics of the incident particles over the interval [ a, b ] in the designated calculation region is C and the probability density function is f (x), then:
Wherein N i >0 is a constant, 0.ltoreq.g i (x).ltoreq.1, and f i (x) is a normalized probability density function over the interval [ a, b ], then taking g i (x) as a criterion, sampling f i (x) can be constructed to realize analog sampling of f (x); the particles at a given position in space will pass a certain distance in the medium until the next event occurs, and their mean free path is:
Wherein N is the type of substances in the medium, N i is the proportion of the ith substance in the medium, and sigma (Z i, E) is the total differential reaction cross section of the material corresponding to the substance; for a segment with multiple medium paths, the number of the particles passing through the mean free path is n λ, and if n r is the number of the particles passing through the mean free path from the starting point to the position of the nuclear event, the distribution is that Let ζ be a random variable obeying a uniform distribution over the interval (0, 1), then:
The method is characterized in that the average free path number from the starting point to the position where the nuclear event occurs is sampled, so that the track length delta x of the particle with one-time action can be obtained, and the simulation of the particle transportation process is realized.
10. The method according to claim 9, wherein in the pulse shaper output pulse waveform of step S3, a transfer function of a system formed by the detector and the preamplifier is:
Wherein p k is the pole of the analog system, and the pole is obtained after digitizing by taking T as the sampling period:
The method can be used for obtaining after finishing:
wherein P k and Z l are respectively poles and zeros of the digital system, and r is a constant, and a differential equation of the output signal is written:
Where x (T) is an input signal sequence with T as a sampling period, and y (T) is a desired pulse waveform signal.
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