CN113126140A - System and method for real-time discrimination of high-speed digital n/gamma waveforms - Google Patents
System and method for real-time discrimination of high-speed digital n/gamma waveforms Download PDFInfo
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Abstract
The invention belongs to the technical field of nuclear radiation detection, and particularly relates to a high-speed digital n/gamma waveform real-time discrimination system and a method. And combining the area value after pulse normalization and the back edge time to achieve the aim of high-speed real-time discrimination of the n/gamma rays. The invention overcomes the defects of poor stability and limited allowable counting rate measurement range of the traditional analog waveform discrimination system, and can operate in a higher counting rate environment; the invention adopts the time-alternating parallel sampling technology, overcomes the high-speed and high-precision limitation of the existing analog-digital conversion device, and greatly improves the speed and precision of a sampling system; the invention overcomes the defect of poor timeliness of the measurement result of the digital off-line waveform discrimination system and can discriminate in real time at high speed; the waveform discrimination system provided by the invention has the advantages of compact volume, low power consumption, portability and application in field work.
Description
Technical Field
The invention belongs to the technical field of nuclear radiation detection, and particularly relates to a high-speed digital n/gamma waveform real-time discrimination system and a method.
Background
In neutron detection, gamma ray interference is inevitably accompanied, and most of medium materials applied to detect neutrons are sensitive to gamma rays, so that the accuracy of measurement results is deteriorated, and therefore, it is necessary to discriminate n/gamma rays. Neutrons and gamma rays are incident on the scintillator detector, and the electrical pulses collected by the photomultiplier tube anode differ in shape. Waveform discrimination mainly discriminates the type of incident particles according to the difference of pulse shapes, and is widely applied to the fields of particle detection, environmental radiation detection, geological exploration, deep space detection and the like at present.
Although the waveform discrimination method based on the analog circuit technology can realize the particle discrimination effect to a certain extent, the current measurement requirements are difficult to meet due to the fact that an analog signal processing hardware system is complex and large in scale and inevitable limitations exist in the aspects of signal processing speed, processing precision, system counting overload resistance, discrimination algorithm flexibility and the like. With the rapid development of digital signal processing technology and digital processing devices in recent years, a firm technical foundation is laid for the discrimination of digital waveforms. The high-speed ADC is used for digitally sampling the full pulse waveform, then the sampling quantity is sent to the digital unit for processing, and finally a measurement result is obtained through a discrimination algorithm.
The existing digital waveform discrimination technology mainly comprises offline discrimination and real-time discrimination, and the digital real-time discrimination scheme of the waveform is more ideal based on the timeliness required by the measurement result. Digitally sampling the full waveform of pulses output by the scintillator detector; after the data stream is input into the FPGA, a corresponding algorithm is designed to complete effective discrimination of the digital pulse; and finally, transmitting the measurement result to an upper computer for display in real time through a serial port. The real-time screening of the digital waveforms can reduce the dead time of the system, so that the screening algorithm is more flexible in design, and the system is allowed to operate in a higher counting rate environment on the basis of meeting the timeliness of measurement results.
Disclosure of Invention
Aiming at the defects, the invention mainly aims to provide a high-speed digital n/gamma waveform real-time discrimination system and a method for the current situation that the real-time discrimination effect is not ideal when the current n/gamma discrimination is applied to a high counting rate environment, and the high-speed real-time discrimination of n/gamma rays is achieved by combining the parameter characteristics of two parts, namely an area value and a back edge time after pulse normalization.
The technical scheme of the invention is as follows:
a high-speed digital n/gamma waveform real-time discrimination system comprises a BC501A type liquid scintillator detector, a dual-channel high-speed AD parallel alternate sampling circuit, an FPGA processing unit and an upper computer;
the BC501A type liquid scintillator detector divides signals into two paths and transmits the signals to two AD9684 chips with 14 bits and 500mps, the chips carry out primary processing on data and then gather and transmit the processed data to the FPGA processing unit, the FPGA processing unit further processes the signals and then transmits the final processing result to the upper computer;
the device comprises a high-speed parallel alternate sampling AD circuit consisting of two AD9684 chips with 14 sampling bits and 500MSps sampling rate, an FPGA digital processing unit consisting of an xc7a100tfgg4842l chip and an RS232 serial port data transmitting circuit;
the electric pulse output by the detector module is amplified, signal conditioning such as single-ended to LVDS differential type conversion is carried out, and then the electric pulse is sent into a high-speed AD circuit to carry out full waveform digital sampling;
integrating digital signals with the sampling bit number of 14 bits and the sampling rate of 500MSPS into data streams with 14 bits and 1GSps of a single channel in an FPGA, and processing and discriminating the signals by utilizing an algorithm; and finally, sending the related discrimination parameters and the particle measurement parameters to an upper computer through a serial port, and displaying the two-dimensional distribution of the discrimination parameters and corresponding neutron and gamma spectrums.
The specific steps of real-time waveform discrimination are as follows;
1) the n/gamma rays are incident into a BC501A type liquid scintillator detector, and an anode of a photomultiplier tube collects electric pulse signals;
2) after the analog pulse signal is simply conditioned, the analog pulse signal is connected with a double-channel AD sampling circuit to be alternately sampled in parallel at a high speed, and the full waveform is quantized into a digital signal;
3) two-channel parallel sampling data streams are input into an FPGA, and the two-channel signals are firstly spliced and integrated into a single-channel data stream with double sampling rate in the FPGA; then carrying out digital filtering smoothing, threshold value discrimination, baseline estimation and recovery, accumulation discrimination and other processing on the data stream; finally, two parts of discrimination parameters of the area value and the back porch time after pulse normalization are extracted; combining the two parts of screening parameter characteristics, and comprehensively comparing the two parts of screening parameter characteristics with set threshold parameters to finally determine the particle type;
4) packaging the measurement data according to the content of the communication protocol, and sending the measurement data to an RS232 serial port sending module; 5) after the upper computer receives the effective measurement data, displaying the two-dimensional distribution of the discrimination parameters and corresponding neutron and gamma spectrum distribution;
the specific steps of the step 5) are as follows: 5.1) the upper computer receives the data packet sent by the serial port and analyzes the data packet according to a communication protocol; 5.2) performing CRC verification on the data in the data packet, comparing a verification result with a verification value of a packet tail, and judging the accuracy of the data; and 5.3) displaying the measured data in the effective data packet, and displaying a two-dimensional distribution result of the discrimination parameters and corresponding neutron and gamma spectrum distribution.
The specific steps of the step 2) are as follows: 2.1) amplifying the analog signal output by the anode of the photomultiplier and conditioning the single-ended signal to LVDS differential signal; 2.2) the conditioned analog signal is accessed into a high-speed AD sampling circuit to complete full waveform digital sampling; in order to realize the system sampling indexes of 1GSps and 14-bit sampling precision and the simulation bandwidth reaching 2GHz, two AD9684 chips with the sampling precision of 14 bits and the sampling rate of 500MSps are selected to complete the design of a dual-channel alternative parallel sampling system; and 2.3) configuring an ADC (analog to digital converter) sampling clock and chip selection and other signal input by the FPGA based on the time alternation parallel sampling technical principle to finish the related sampling process.
The specific steps of the step 3) are as follows: 3.1) splicing and integrating two channels of data point by point in an FPGA into a digital data stream with a single channel sampling bit number of 14 bits and a sampling rate of 1 GSps; 3.2) selecting a proper filtering algorithm for noise reduction according to the frequency spectrum characteristics of the digital signal; 3.3) comparing the threshold value of the sampling quantity point by point, if the sampling quantity is continuously and repeatedly larger than the set threshold value, considering that an effective nuclear pulse is detected, wherein the moment is the initial moment of arrival of the nuclear pulse; if the sampling quantity is continuously less than the set threshold value for multiple times at the trailing edge moment of the pulse, the pulse is considered to be ended; the time period lasting from the pulse starting time to the pulse ending time is a valid kernel pulse interval; 3.4) in the invalid nuclear pulse range, calculating the average value of the selected 64 sampling quantities according to a baseline estimation algorithm, wherein the numerical result is used as the baseline value of the upcoming adjacent pulse, and the final baseline restoration result is the original sampling quantity minus the baseline estimation value; 3.5) carrying out accumulation identification on the digital signals, if the pulses are accumulated, removing the pulses, and then carrying out counting rate correction; 3.6) extracting parameters of the pulse without accumulation to obtain two discrimination parameters of an area value and a back porch time after pulse normalization; 3.7) comprehensively comparing the area value and the back edge time after the pulse normalization with the set threshold respectively, and finally determining the type of the incident particle.
The specific steps of the step 4) are as follows: 4.1) designing a serial port communication protocol, packaging the measurement result, adding a packet header identification code to the data packet, and adding the measurement data as a CRC-16 check result as a packet tail; and 4.2) sending the data packet to an upper computer through RS 232.
The data integration in the step 4) is based on the time alternation parallel sampling technical principle, the sampling quantities of 14 bits and 500MSps of the two channels are interpolated point by point, and the sampling quantities are integrated into a digital signal stream of 14 bits and 1GSps of a single channel, so that the precision and the speed of a sampling system are improved;
the filtering smoothing is to perform noise reduction processing on the signal by adopting a multipoint filtering smoothing method, so that the influence of noise on a measurement result is reduced;
judging the threshold value, comparing the threshold value of the sampling quantity point by point, and if the numerical value of the sampling quantity is continuously and repeatedly greater than the set threshold value, determining that an effective nuclear pulse is detected, wherein the moment is the initial moment of the nuclear pulse; and if the sampling value is less than the set threshold value continuously for multiple times at the trailing edge time of the pulse, the nuclear pulse is considered to be ended, the time is the nuclear pulse ending time, and the range from the pulse starting time to the pulse ending time is an effective nuclear pulse interval.
The method for estimating the digital baseline by the baseline estimation in the step 4) is characterized in that under the state without a nuclear signal, the average value of 64 sampling points meeting the requirements is intelligently selected in real time according to the dynamic state of a counting rate environment to serve as a baseline value; by carrying out digital baseline restoration on the signals, the influence of baseline shift on energy spectrum acquisition can be reduced;
the method for rejecting digital accumulation rejection comprises the steps of detecting two adjacent nuclear pulses, and judging whether the value of the sampling quantity at the moment is larger than a set threshold value when the back edge stage of the current pulse jumps to the front edge of the next pulse; if the sampling quantity is larger than a set threshold value, the pulse is judged to be piled up, and the pulse is abandoned in subsequent processing; if the amplitude is smaller than the threshold value, the signal is considered to be a normal signal;
the amplitude value of the pulse is extracted by the discrimination algorithm in the step 4), the area value and the back porch time after the pulse normalization are calculated, and the type of the incident particle is finally determined by combining the two parts of parameter characteristics and comprehensively comparing the two parts of parameter characteristics with a set threshold; screening threshold values are acquired by carrying out large-quantity statistics on area and trailing edge time values after n/gamma waveform normalization before experiments, and then setting a corresponding appropriate threshold value range according to a fitting distribution rule;
the serial port communication 7 packs the measurement data according to a serial port communication protocol, adds an identification code as a packet head, uses a CRC-16 check result of the measurement data as a packet tail, and sends the whole packet of data to an upper computer in real time through an RS232 serial port;
amplitude extraction adopts a trapezoidal filter forming method to extract the amplitude of the nuclear pulse, and the amplitude information of the pulse is extracted in real time;
the back porch time calculation takes the constant f1, f2 trigger ratio of the pulse amplitude A as the upper threshold and the lower threshold of the pulse trigger in the back porch part of the pulse;
3) counting the number N of sampling quantities within the range of an upper threshold and a lower threshold of the pulse trailing edge part;
4) calculating the trailing edge time of the pulse, namely multiplying the number of the sampling quantity by the clock period;
and calculating the normalized area of the pulse within the range of the effective pulse interval, accumulating and summing the digital sampling quantity to obtain the area of the whole pulse, dividing the area value of the pulse by the amplitude value, and calculating the area value result after the pulse normalization.
And comprehensively comparing the area threshold value and the back edge time threshold value 4 with the corresponding area threshold value and the back edge time threshold value in combination with the parameter information of the area value and the back edge time parameter after the pulse normalization, and finally determining the type of the incident particles.
The invention has the beneficial effects that:
(1) the invention overcomes the defects of poor stability and limited allowable counting rate measurement range of the traditional analog waveform discrimination system, and can operate in a higher counting rate environment;
(2) the invention adopts the time-alternating parallel sampling technology, overcomes the high-speed and high-precision limitation of the existing analog-digital conversion device, and greatly improves the speed and precision of a sampling system;
(3) the invention overcomes the defect of poor timeliness of the measurement result of the digital off-line waveform discrimination system and can discriminate in real time at high speed;
(4) the waveform discrimination system provided by the invention has the advantages of compact volume, low power consumption, portability and application in field work.
Drawings
Fig. 1 is a schematic diagram of a high-speed digital n/gamma waveform real-time discrimination method according to the present invention.
Fig. 2 is a hardware system block diagram of a high-speed digital n/gamma waveform real-time discrimination method provided by the invention.
Fig. 3 is a signal processing flow chart of a high-speed digital n/gamma waveform real-time discrimination method provided by the invention.
Fig. 4 is a flow chart of an implementation of a high-speed digital n/gamma waveform real-time discrimination algorithm provided by the invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the embodiments.
A high-speed digital n/gamma waveform real-time discrimination system comprises a BC501A type liquid scintillator detector, a dual-channel high-speed AD parallel alternate sampling circuit, an FPGA processing unit and an upper computer.
BC501A type liquid scintillator detector divides the signal into two the way and sends to the AD9684 chip of two 14 bit, 500mps, and the chip carries out preliminary treatment with data and then gathers the data that will handle and send to FPGA processing unit, and FPGA processing unit further processes the signal, sends the last processing result to the host computer again.
A high-speed digital n/gamma waveform real-time discrimination method comprises the following specific steps: 1) the n/gamma rays are incident into a BC501A type liquid scintillator detector, and an anode of a photomultiplier tube collects electric pulse signals; 2) after the analog pulse signal is simply conditioned, the analog pulse signal is connected with a double-channel AD sampling circuit to be alternately sampled in parallel at a high speed, and the full waveform is quantized into a digital signal; 3) two-channel parallel sampling data streams are input into an FPGA, and the two-channel signals are firstly spliced and integrated into a single-channel data stream with double sampling rate in the FPGA; then carrying out digital filtering smoothing, threshold value discrimination, baseline estimation and recovery, accumulation discrimination and other processing on the data stream; and finally, extracting two parts of discrimination parameters of the area value and the back edge time after pulse normalization. Combining the two parts of screening parameter characteristics, and comprehensively comparing the two parts of screening parameter characteristics with set threshold parameters to finally determine the particle type; 4) packaging the measurement data according to the content of the communication protocol, and sending the measurement data to an RS232 serial port sending module; 5) and after the upper computer receives the effective measurement data, displaying the two-dimensional distribution of the discrimination parameters and corresponding neutron and gamma spectrum distribution.
The specific steps of the step 2) are as follows: 2.1) amplifying the analog signal output by the anode of the photomultiplier and conditioning the single-ended signal to LVDS differential signal; 2.2) the conditioned analog signal is connected to a high-speed AD sampling circuit to complete full-waveform digital sampling. In order to realize the system sampling indexes of 1GSps and 14-bit sampling precision and the analog bandwidth reaching 2GHz, two AD9684 chips with the sampling precision of 14 bits and the sampling rate of 500MSps are selected to complete the design of a dual-channel alternative parallel sampling system. And 2.3) configuring an ADC (analog to digital converter) sampling clock and chip selection and other signal input by the FPGA based on the time alternation parallel sampling technical principle to finish the related sampling process.
The specific steps of the step 3) are as follows: 3.1) splicing and integrating two channels of data point by point in an FPGA into a digital data stream with a single channel sampling bit number of 14 bits and a sampling rate of 1 GSps; 3.2) selecting a proper filtering algorithm for noise reduction according to the frequency spectrum characteristics of the digital signal; 3.3) comparing the threshold value of the sampling quantity point by point, if the sampling quantity is continuously and repeatedly larger than the set threshold value, considering that an effective nuclear pulse is detected, wherein the moment is the initial moment of arrival of the nuclear pulse; and if the sampling quantity is less than the set threshold value continuously for multiple times at the trailing edge time of the pulse, the pulse is considered to be ended. The time period lasting from the pulse starting time to the pulse ending time is a valid kernel pulse interval; 3.4) in the invalid nuclear pulse range, calculating the average value of the selected 64 sampling quantities according to a baseline estimation algorithm, wherein the numerical result is used as the baseline value of the upcoming adjacent pulse, and the final baseline restoration result is the original sampling quantity minus the baseline estimation value; 3.5) carrying out accumulation identification on the digital signals, if the pulses are accumulated, removing the pulses, and then carrying out counting rate correction; 3.6) extracting parameters of the pulse without accumulation to obtain two discrimination parameters of an area value and a back porch time after pulse normalization; 3.7) comprehensively comparing the area value and the back edge time after the pulse normalization with the set threshold respectively, and finally determining the type of the incident particle.
The specific steps of the step 4) are as follows: 4.1) designing a serial port communication protocol, packaging the measurement result, adding a packet header identification code to the data packet, and adding the measurement data as a CRC-16 check result as a packet tail; and 4.2) sending the data packet to an upper computer through RS 232.
The specific steps of the step 5) are as follows: 5.1) the upper computer receives the data packet sent by the serial port and analyzes the data packet according to a communication protocol; 5.2) performing CRC verification on the data in the data packet, comparing a verification result with a verification value of a packet tail, and judging the accuracy of the data; and 5.3) displaying the measured data in the effective data packet, and displaying a two-dimensional distribution result of the discrimination parameters and corresponding neutron and gamma spectrum distribution.
The BC501A type liquid scintillator detector has better time characteristic, pulse shape discrimination capability and neutron detection efficiency.
The particles are incident into a detector and ionized and excited with a scintillator substance, and the energy deposited in the scintillator emits fluorescence photons in a de-excitation mode; then the fluorescence photons reach the photocathode of the photomultiplier through the light guide and the optical coupling agent, and photoelectrons are emitted in the whole process; finally, photoelectrons are multiplied in a photomultiplier, and corresponding electric pulse signals are collected on the anode so as to realize the detection of particles. After the interaction between the neutrons and the scintillator, the recoil protons are mainly generated; and secondary electrons are generated after the interaction between the gamma rays and the scintillator material. The fluorescence pulses excited by different charged particles contain components with different durations, and the intensity ratio of the fast and slow components is related to the ionization density formed by the charged particles in the scintillator detector. The energy deposition density of the recoil proton in the scintillator is larger, and the decay time of the excited fluorescence pulse is longer. The energy deposition density of the secondary electrons in the scintillator is low, the proportion of transient photons is high in the process of de-excitation luminescence, and the decay time of the excited fluorescence pulse is short. Fig. 1 shows a normalized result of an n/gamma waveform output by an anode of a BC501A type liquid scintillator detector, wherein the waveform results of two types of particles are almost consistent in a pulse leading edge part, and the decay time of a neutron waveform is longer in a pulse trailing edge stage, so that waveform discrimination can be performed according to the difference in the aspect. The principle and the implementation process of the high-speed digital n/gamma waveform real-time discrimination method provided by the invention are as follows: 1) firstly, extracting an amplitude value A of a pulse; 2) the constant f1 and f2 trigger ratios of the amplitude A are used as a lower threshold and an upper threshold of pulse trailing edge triggering in the pulse trailing edge part; 3) counting the number N of sampling quantities within the lower threshold range and the upper threshold range; 4) the trailing edge time of the pulse is the number of samples times the sampling clock period. The shorter the sampling clock period is, the higher the accuracy of the n/gamma waveform discrimination result is; 5) and in the effective range of the pulse, the sampling amount is accumulated and summed and then divided by the amplitude value of the pulse to obtain the area value after the pulse normalization.
Fig. 2 is a hardware system block diagram of the high-speed digital n/gamma waveform real-time discrimination method provided by the invention, which mainly comprises a high-speed parallel alternate sampling AD circuit composed of two AD9684 chips with 14 bits of sampling bits and a sampling rate of 500MSps, an FPGA digital processing unit composed of an xc7a100tfgg4842l chip, and an RS232 serial port data transmission circuit. The electric pulse output by the detector module is amplified, signal conditioning such as single-ended to LVDS differential type conversion is carried out, and then the electric pulse is sent into a high-speed AD circuit to carry out full waveform digital sampling; integrating digital signals with the sampling bit number of 14 bits and the sampling rate of 500MSPS into data streams with 14 bits and 1GSps of a single channel in an FPGA, and processing and discriminating the signals by utilizing an algorithm; and finally, sending the related discrimination parameters and the particle measurement parameters to an upper computer through a serial port, and displaying the two-dimensional distribution of the discrimination parameters and corresponding neutron and gamma spectrums.
Fig. 3 is a signal processing flow of the high-speed real-time digital n/γ waveform discrimination method provided by the present invention, and the specific signal processing flow is as follows:
the data integration 1 is based on the time alternation parallel sampling technology principle, interpolates the sampling quantity of 14 bits and 500MSps of two channels point by point, and integrates the sampling quantity into a digital signal flow of 14 bits and 1GSps of a single channel, thereby improving the precision and the speed of a sampling system.
And the filtering smoothing 2 is used for carrying out noise reduction processing on the signal by adopting a multipoint filtering smoothing method, so that the influence of noise on the measurement result is reduced.
Threshold value discrimination 3 compares the sampling quantity threshold value point by point, if the sampling quantity numerical value is continuously and repeatedly greater than the set threshold value, a valid nuclear pulse is considered to be detected, and the moment is the nuclear pulse starting moment; and if the sampling value is less than the set threshold value continuously for multiple times at the trailing edge time of the pulse, the nuclear pulse is considered to be ended, the time is the nuclear pulse ending time, and the range from the pulse starting time to the pulse ending time is an effective nuclear pulse interval.
The baseline estimation 4 digital baseline estimation method is that under the state without nuclear signals, the average value of 64 sampling points meeting the requirements is intelligently selected in real time according to the counting rate environment dynamic state to be used as a baseline value. By performing digital baseline restoration on the signal, the effect of baseline shift on the energy spectrum acquisition can be reduced.
The digital accumulation rejection method of accumulation rejection 5 is to detect two adjacent nuclear pulses, and judge whether the value of the sampling quantity at the moment is larger than the set threshold value when the back edge stage of the current pulse jumps to the front edge of the next pulse. If the sampling quantity is larger than a set threshold value, the pulse is judged to be piled up, and the pulse is abandoned in subsequent processing; if the amplitude is smaller than the threshold value, the signal is considered to be a normal signal.
The discrimination algorithm 6 extracts the amplitude value of the pulse, calculates the area value and the back edge time after the pulse normalization, and comprehensively compares the two parts of parameter characteristics with a set threshold value to finally determine the type of the incident particles. The acquisition of the discrimination threshold value needs to be carried out by carrying out a large amount of statistics on the normalized area and trailing edge time values of the n/gamma waveform before the experiment, and then setting a corresponding appropriate threshold value range according to a fitting distribution rule.
The serial port communication 7 packs the measurement data according to a serial port communication protocol, adds an identification code as a packet header, uses a CRC-16 check result of the measurement data as a packet tail, and sends the whole packet of data to an upper computer in real time through an RS232 serial port.
FIG. 4 is a flow chart of implementing a high-speed digital n/gamma waveform real-time discrimination algorithm provided by the invention, which comprises the following specific steps:
Back porch time calculation 2 takes constant f1, f2 trigger ratios of pulse amplitude a as the upper and lower thresholds of pulse triggering during the back porch portion of the pulse; 3) counting the number N of sampling quantities within the range of an upper threshold and a lower threshold of the pulse trailing edge part; 4) and calculating the trailing edge time of the pulse, namely multiplying the number of the sampling amount by the clock period.
And (3) in the range of the effective pulse interval, performing accumulated summation on the digital sampling quantity to obtain the area of the whole pulse, dividing the area value of the pulse by the amplitude value, and calculating the area value result after the pulse normalization.
And comprehensively comparing the area threshold value and the back edge time threshold value 4 with the corresponding area threshold value and the back edge time threshold value in combination with the parameter information of the area value and the back edge time parameter after the pulse normalization, and finally determining the type of the incident particles.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention, but rather as the following claims are included in the present invention.
Claims (10)
1. A high-speed digital n/gamma waveform real-time discrimination system comprises a BC501A type liquid scintillator detector, a dual-channel high-speed AD parallel alternate sampling circuit, an FPGA processing unit and an upper computer;
the method is characterized in that: the BC501A type liquid scintillator detector divides signals into two paths and transmits the signals to two AD9684 chips with 14 bits and 500mps, the chips carry out primary processing on data and then gather and transmit the processed data to the FPGA processing unit, the FPGA processing unit further processes the signals and then transmits the final processing result to the upper computer;
the device comprises a high-speed parallel alternate sampling AD circuit consisting of two AD9684 chips with 14 sampling bits and 500MSps sampling rate, an FPGA digital processing unit consisting of an xc7a100tfgg4842l chip and an RS232 serial port data transmitting circuit;
the electric pulse output by the detector module is amplified, signal conditioning such as single-ended to LVDS differential type conversion is carried out, and then the electric pulse is sent into a high-speed AD circuit to carry out full waveform digital sampling;
integrating digital signals with the sampling bit number of 14 bits and the sampling rate of 500MSPS into data streams with 14 bits and 1GSps of a single channel in an FPGA, and processing and discriminating the signals by utilizing an algorithm; and finally, sending the related discrimination parameters and the particle measurement parameters to an upper computer through a serial port, and displaying the two-dimensional distribution of the discrimination parameters and corresponding neutron and gamma spectrums.
2. A high-speed digital n/gamma waveform real-time discrimination method is characterized in that: the specific steps of real-time waveform discrimination are as follows;
1) the n/gamma rays are incident into a BC501A type liquid scintillator detector, and an anode of a photomultiplier tube collects electric pulse signals;
2) after the analog pulse signal is simply conditioned, the analog pulse signal is connected with a double-channel AD sampling circuit to be alternately sampled in parallel at a high speed, and the full waveform is quantized into a digital signal;
3) two-channel parallel sampling data streams are input into an FPGA, and the two-channel signals are firstly spliced and integrated into a single-channel data stream with double sampling rate in the FPGA; then carrying out digital filtering smoothing, threshold value discrimination, baseline estimation and recovery, accumulation discrimination and other processing on the data stream; finally, two parts of discrimination parameters of the area value and the back porch time after pulse normalization are extracted; combining the two parts of screening parameter characteristics, and comprehensively comparing the two parts of screening parameter characteristics with set threshold parameters to finally determine the particle type;
4) packaging the measurement data according to the content of the communication protocol, and sending the measurement data to an RS232 serial port sending module; 5) after the upper computer receives the effective measurement data, displaying the two-dimensional distribution of the discrimination parameters and corresponding neutron and gamma spectrum distribution;
the specific steps of the step 5) are as follows: 5.1) the upper computer receives the data packet sent by the serial port and analyzes the data packet according to a communication protocol; 5.2) performing CRC verification on the data in the data packet, comparing a verification result with a verification value of a packet tail, and judging the accuracy of the data; and 5.3) displaying the measured data in the effective data packet, and displaying a two-dimensional distribution result of the discrimination parameters and corresponding neutron and gamma spectrum distribution.
3. The method for real-time discrimination of high-speed digital n/gamma waveforms according to claim 2, wherein: the specific steps of the step 2) are as follows: 2.1) amplifying the analog signal output by the anode of the photomultiplier and conditioning the single-ended signal to LVDS differential signal; 2.2) the conditioned analog signal is accessed into a high-speed AD sampling circuit to complete full waveform digital sampling; in order to realize the system sampling indexes of 1GSps and 14-bit sampling precision and the simulation bandwidth reaching 2GHz, two AD9684 chips with the sampling precision of 14 bits and the sampling rate of 500MSps are selected to complete the design of a dual-channel alternative parallel sampling system; and 2.3) configuring an ADC (analog to digital converter) sampling clock and chip selection and other signal input by the FPGA based on the time alternation parallel sampling technical principle to finish the related sampling process.
4. The method for real-time discrimination of high-speed digital n/gamma waveforms according to claim 2, wherein: the specific steps of the step 3) are as follows: 3.1) splicing and integrating two channels of data point by point in an FPGA into a digital data stream with a single channel sampling bit number of 14 bits and a sampling rate of 1 GSps; 3.2) selecting a proper filtering algorithm for noise reduction according to the frequency spectrum characteristics of the digital signal; 3.3) comparing the threshold value of the sampling quantity point by point, if the sampling quantity is continuously and repeatedly larger than the set threshold value, considering that an effective nuclear pulse is detected, wherein the moment is the initial moment of arrival of the nuclear pulse; if the sampling quantity is continuously less than the set threshold value for multiple times at the trailing edge moment of the pulse, the pulse is considered to be ended; the time period lasting from the pulse starting time to the pulse ending time is a valid kernel pulse interval; 3.4) in the invalid nuclear pulse range, calculating the average value of the selected 64 sampling quantities according to a baseline estimation algorithm, wherein the numerical result is used as the baseline value of the upcoming adjacent pulse, and the final baseline restoration result is the original sampling quantity minus the baseline estimation value; 3.5) carrying out accumulation identification on the digital signals, if the pulses are accumulated, removing the pulses, and then carrying out counting rate correction; 3.6) extracting parameters of the pulse without accumulation to obtain two discrimination parameters of an area value and a back porch time after pulse normalization; 3.7) comprehensively comparing the area value and the back edge time after the pulse normalization with the set threshold respectively, and finally determining the type of the incident particle.
5. The method for real-time discrimination of high-speed digital n/gamma waveforms according to claim 2, wherein: the specific steps of the step 4) are as follows: 4.1) designing a serial port communication protocol, packaging the measurement result, adding a packet header identification code to the data packet, and adding the measurement data as a CRC-16 check result as a packet tail; and 4.2) sending the data packet to an upper computer through RS 232.
6. The method of claim 5 for real-time discrimination of high-speed digital n/gamma waveforms, wherein: the data integration in the step 4) is based on the time alternation parallel sampling technical principle, the sampling quantities of 14 bits and 500MSps of the two channels are interpolated point by point, and the sampling quantities are integrated into a digital signal stream of 14 bits and 1GSps of a single channel, so that the precision and the speed of a sampling system are improved;
the filtering smoothing is to perform noise reduction processing on the signal by adopting a multipoint filtering smoothing method, so that the influence of noise on a measurement result is reduced;
judging the threshold value, comparing the threshold value of the sampling quantity point by point, and if the numerical value of the sampling quantity is continuously and repeatedly greater than the set threshold value, determining that an effective nuclear pulse is detected, wherein the moment is the initial moment of the nuclear pulse; and if the sampling value is less than the set threshold value continuously for multiple times at the trailing edge time of the pulse, the nuclear pulse is considered to be ended, the time is the nuclear pulse ending time, and the range from the pulse starting time to the pulse ending time is an effective nuclear pulse interval.
7. The method of claim 5 for real-time discrimination of high-speed digital n/gamma waveforms, wherein: the method for estimating the digital baseline by the baseline estimation in the step 4) is characterized in that under the state without a nuclear signal, the average value of 64 sampling points meeting the requirements is intelligently selected in real time according to the dynamic state of a counting rate environment to serve as a baseline value; by carrying out digital baseline restoration on the signals, the influence of baseline shift on energy spectrum acquisition can be reduced;
the method for rejecting digital accumulation rejection comprises the steps of detecting two adjacent nuclear pulses, and judging whether the value of the sampling quantity at the moment is larger than a set threshold value when the back edge stage of the current pulse jumps to the front edge of the next pulse; if the sampling quantity is larger than a set threshold value, the pulse is judged to be piled up, and the pulse is abandoned in subsequent processing; if the amplitude is smaller than the threshold value, the signal is considered to be a normal signal.
8. The method of claim 5 for real-time discrimination of high-speed digital n/gamma waveforms, wherein: the amplitude value of the pulse is extracted by the discrimination algorithm in the step 4), the area value and the back porch time after the pulse normalization are calculated, and the type of the incident particle is finally determined by combining the two parts of parameter characteristics and comprehensively comparing the two parts of parameter characteristics with a set threshold; screening threshold values are acquired by carrying out large-quantity statistics on area and trailing edge time values after n/gamma waveform normalization before experiments, and then setting a corresponding appropriate threshold value range according to a fitting distribution rule;
the serial port communication 7 packs the measurement data according to a serial port communication protocol, adds an identification code as a packet header, uses a CRC-16 check result of the measurement data as a packet tail, and sends the whole packet of data to an upper computer in real time through an RS232 serial port.
9. The method for real-time discrimination of high-speed digital n/gamma waveforms according to claim 2, wherein: amplitude extraction adopts a trapezoidal filter forming method to extract the amplitude of the nuclear pulse, and the amplitude information of the pulse is extracted in real time;
the back porch time calculation takes the constant f1, f2 trigger ratio of the pulse amplitude A as the upper threshold and the lower threshold of the pulse trigger in the back porch part of the pulse;
3) counting the number N of sampling quantities within the range of an upper threshold and a lower threshold of the pulse trailing edge part;
4) calculating the trailing edge time of the pulse, namely multiplying the number of the sampling quantity by the clock period;
and calculating the normalized area of the pulse within the range of the effective pulse interval, accumulating and summing the digital sampling quantity to obtain the area of the whole pulse, dividing the area value of the pulse by the amplitude value, and calculating the area value result after the pulse normalization.
10. The method for real-time discrimination of high-speed digital n/gamma waveforms according to claim 9, wherein: and comprehensively comparing the area threshold value and the back edge time threshold value 4 with the corresponding area threshold value and the back edge time threshold value in combination with the parameter information of the area value and the back edge time parameter after the pulse normalization, and finally determining the type of the incident particles.
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