A method for generating simulated signals for a position-sensitive 3He tube neutron detector

Abstract

This invention discloses a method for generating simulated signals for a position-sensitive 3He tube neutron detector. The method obtains the random distribution function of the total pulse amplitude of a single particle impact, the random distribution function of the time interval between neutron impacts on the detector, and the random position distribution function of the neutron impact on the 3He tube. Based on these functions, the invention constructs digital waveform pulses of the signals at both ends of the 3He tube. These digital waveform pulses are then converted into two real pulse signals via two DACs. Furthermore, these two pulse signal sources are simulated signal sources capable of containing energy, time, and position distribution information for neutron detection by a position-sensitive 3He tube neutron detector. This invention will greatly contribute to the development of corresponding readout electronics, particularly in the fields of position measurement algorithm optimization and position measurement accuracy calibration.

Description

Technical Field

[0001] This invention relates to the field of signal simulation and testing technology, and in particular to a method for generating simulation signals for a position-sensitive 3He tube neutron detector. Background Technology

[0002] The discovery and application of the neutron is one of the most important scientific and technological achievements of the 20th century. Neutron detection is widely used for reactor nuclear power measurement or core neutron flux distribution measurement. Simultaneously, as a special electrically neutral particle, the neutron possesses a magnetic moment. Compared with X-ray diffraction, neutron scattering technology has irreplaceable advantages such as extremely strong penetrating power, sensitivity to light elements, isotope resolution, magnetic microscopic analysis, and non-destructive nature. In these neutron detection applications, especially neutron scattering imaging, position-sensitive measurements are often required to obtain information about the internal structure of the sample.

[0003] The 3He (helium-3) proportional counter is a highly efficient detector for neutrons, often used to efficiently measure the intensity of thermal and hyperthermal neutrons. Compared to other proportional counters, the 3He proportional counter has higher detection efficiency and a wider energy response range. When a neutron strikes the 3He tube detector, the charge generated by gas ionization flows along the anode wire to both ends of the detector. By measuring the difference in signals across the two ends of the 3He tube neutron detector, the location of the neutron impact can be determined. Therefore, the 3He tube detector is widely used for position-sensitive neutron detection.

[0004] Typically, a position-sensitive 3He tube detector array can be used to measure the two-dimensional position of neutrons. The resolution of the entire system depends on both the accuracy of the 3He tube itself and the performance of the readout electron charge measurement and position calculation algorithms. The readout electron system first converts the charge signal across the 3He tube into a voltage signal using a charge-sensitive amplifier; then, through analog-to-digital conversion, it obtains the amplitude of the voltage signal; finally, through digital signal processing and using a specific algorithm, it compares the difference in amplitude between the two signals to determine the position of the particle impact.

[0005] In the development of readout electronics for position-sensitive 3He tube detectors, testing and calibration using 3He tube detectors are necessary to verify overall position resolution performance. However, 3He tube detectors are rare, expensive, and have long lead times due to the scarcity of the inert gas 3He (an isotope of He). Therefore, in the early stages of development, commercial signal sources are typically used instead of actual 3He tube detectors and neutron sources to accelerate the development process and reduce costs. However, commercial signal sources generally only output periodic pulse signals and cannot output the neutron energy distribution, neutron time distribution, and especially the neutron position distribution information contained in the detector signal. In recent years, some nuclear simulation signal generators have been reported, which can simulate pulse signals that match the energy and time distribution of particles, but they cannot output two nuclear pulse signals containing particle (neutron) position distribution information. Summary of the Invention

[0006] The purpose of this invention is to provide a method for generating simulation signals for a position-sensitive 3He tube neutron detector.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for generating a simulation signal for a position-sensitive 3He tube neutron detector, comprising the following steps:

[0008] Step 1: Obtain the random distribution function of the total pulse amplitude of a single particle hit, the random distribution function of the time interval between neutron hits on the detector, and the random position distribution function of neutron hits on the 3He tube, respectively.

[0009] Step 2: Construct digital waveform pulses for the signals at both ends of the 3He tube based on the total pulse amplitude random distribution function, the time interval random distribution function of the neutron hitting the detector, and the random position distribution function of the neutron hitting the 3He tube;

[0010] Step 3: Convert the digital waveform pulse into two real pulse signals through two DACs.

[0011] Preferably, the method for obtaining the total pulse amplitude random distribution function includes:

[0012] The charge generated when a neutron strikes a 3He tube detector is proportional to the neutron energy. The detector uses a charge-sensitive preamplifier, whose output pulse amplitude is proportional to the input charge. The total pulse amplitude distribution of the signals at both ends of the 3He tube detector represents the neutron energy distribution. The total pulse amplitude distribution function generated by a neutron striking a 3He tube can be calculated using a specific neutron energy spectrum. The specific steps for obtaining the neutron energy distribution function using a specific neutron energy spectrum are as follows:

[0013] Assume the neutron energy spectrum to be simulated is divided into M channels, from channel 0 to (M-1), and the channel counts are N0 to N.M-1 Then the probability that the neutron's energy is in channel X is:

[0014]

[0015] The probability distribution of falling within the range [0, X] is as follows:

[0016]

[0017] Preferably, the method for obtaining the random distribution function of the time interval between neutron strikes on the detector includes:

[0018] Among these, nuclear events can be considered independent. Given a count rate, the number of neutrons hitting the detector per unit time follows a Poisson distribution. According to the Poisson distribution, the probability of n neutrons appearing within time ΔT is:

[0019]

[0020] in, This is the average count rate of neutrons, and the time interval between neutron appearances (i.e., the pulse time interval) follows an average value of... If the exponential distribution is true, then the random distribution function of the pulse signal time interval t can be obtained from the exponential distribution as follows:

[0021]

[0022] The method for obtaining the random position distribution function of neutrons hitting the 3He tube includes:

[0023] The method for determining the random position distribution function of neutrons hitting a 3He tube depends on the scenario being simulated. In electronics testing scenarios, the most common scenarios are uniform neutron impact positions or single-point impacts by collimated neutrons. In these two cases, the random position distribution function can be directly obtained from the mathematical properties of distribution. For example, for a uniform position distribution, assuming the effective length of the 3He tube is L, the distribution function of the position l of the neutron hitting the 3He tube is:

[0024]

[0025] Preferably, in step 2, the method for constructing the digital waveform pulses of the signals across the 3He tube includes:

[0026] Given that the random distribution function of the pulse signal amplitude is y = F(x), since the probability in the real world cannot be negative, the distribution function F(x) is always monotonically increasing. Therefore, y = F(x) must have an inverse function, that is, x can be obtained by using y. The sampling of parameter x can be replaced by sampling of a uniformly distributed random number y between [0,1], and then the sampled value of x can be obtained through the inverse function.

[0027] If a uniformly distributed 32-bit random number Y1 is obtained by sampling using the Linear Feedback Shift Register (LSFR) method in an FPGA, then there must exist an X1 such that:

[0028]

[0029] In the FPGA, a lookup table is set up. X1 obtained by calculating Y1 through uniform distribution is the random number of the total pulse amplitude generated this time. A similar method is used to obtain the random number of the nuclear pulse time interval and the random number of the neutron hit position.

[0030] In a single neutron impact event, the signal amplitude across the 3He tube depends on the total charge and the particle impact position. Assuming the effective length of the 3He tube is L, the distance from the neutron incident position to end A is X, and the resistance of the anode wire along length X is R. A The resistance of the anode wire corresponding to segment LX is R. B When a neutron is incident at position X of the 3He tube, it reacts with the 3He gas to produce protons and tritium nuclei. During their movement, the protons and tritium nuclei produce electrons. These electrons move towards the anode wire under the influence of the electric field, undergoing avalanche amplification during their movement. The charge reaching the anode wire moves towards both ends of the 3He tube in the form of pulsed currents. The two currents are in opposite directions and have magnitudes i and i', respectively. A (t), i B (t), is inversely proportional to the resistance of each anode wire, i.e., i A (t)=V(t) / R A i B (t)=V(t) / R B Current i A (t), i B (t) After flowing out of the 3He transistor from both the left and right ends, the currents enter the next stage of the amplifier circuit and other electronic components. Finally, the data acquisition system reads the charge values ​​R corresponding to the two currents. A R B ;

[0031] The electronic systems on both sides of the 3He transistor have the same current amplification factor, i.e., Q. A =∫i A (t)dt,Q B =∫i B Then Q(t)dt. A ×R A =Q B ×R B Since the resistance of the anode wire is directly proportional to its length, the equation for the incident position is obtained by conversion:

[0032]

[0033] Meanwhile, due to the voltage U output by the preamplifiers at both ends A and U B Proportional to Q A and Q B Therefore, the relationship between the voltage across the terminals and the total voltage is as follows:

[0034]

[0035]

[0036] Using the above calculation formula, the amplitude of the signals at both ends of the 3He tube to be simulated can be obtained based on the amplitude distribution random number and the hit position random number. Combined with the pulse time interval random number, the digital pulse signals at both ends of the 3He tube can be simulated and synthesized respectively.

[0037] After obtaining the digital pulse signals from both ends of the 3He tube, the digital pulses are converted into real pulse signals through two DAC circuits for 3He readout electronics testing. The relative amplitude of the two pulses contains the neutron impact location information, the sum of the amplitudes of the two pulses contains the neutron energy information, and the pulse time interval contains the neutron count rate information.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] This invention constructs digital waveform pulses of the signals at both ends of the 3He tube based on the random distribution function of the total pulse amplitude, the random distribution function of the time interval between neutron strikes to the detector, and the random position distribution function of neutron strikes to the 3He tube. These digital waveform pulses are then converted into two real pulse signals by two DACs. Furthermore, these two pulse signal sources are simulated signal sources capable of containing energy, time, and position distribution information for neutron detection by the position-resolved 3He tube neutron detector. This invention will greatly contribute to the development of corresponding readout electronics, particularly playing an important role in areas such as position measurement algorithm optimization and position measurement accuracy calibration. Attached Figure Description

[0040] Figure 1 This is a block diagram of the simulation signal generator for the position-sensitive 3He tube neutron detector of the present invention.

[0041] Figure 2 This is a schematic diagram of the charge distribution at both ends of the neutron detector in the 3He method of the present invention;

[0042] Figure 3 This is a schematic diagram of the DAC conversion circuit of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] This invention provides a method for generating simulation signals for a position-sensitive 3He tube neutron detector, comprising the following steps:

[0045] Step 1: Obtain the random distribution function of the total pulse amplitude of a single particle hit, the random distribution function of the time interval between neutron hits on the detector, and the random position distribution function of neutron hits on the 3He tube, respectively.

[0046] Step 2: Construct digital waveform pulses for the signals at both ends of the 3He tube based on the total pulse amplitude random distribution function, the time interval random distribution function of the neutron hitting the detector, and the random position distribution function of the neutron hitting the 3He tube;

[0047] Step 3: Convert the digital waveform pulse into two real pulse signals through two DACs.

[0048] Preferably, the method for obtaining the total pulse amplitude random distribution function includes:

[0049] The charge generated when a neutron strikes a 3He tube detector is proportional to the neutron energy; furthermore, the detector employs a charge-sensitive preamplifier, whose output pulse amplitude is proportional to the input charge. Therefore, we can deduce that the total pulse amplitude distribution of the signals at both ends of the 3He tube detector represents the neutron energy distribution. The total pulse amplitude distribution function generated by a neutron striking a 3He tube can be calculated using a specific neutron energy spectrum. The specific steps for obtaining the neutron energy distribution function using a specific neutron energy spectrum are as follows:

[0050] Assume the neutron energy spectrum to be simulated is divided into M channels, from channel 0 to (M-1), and the channel counts are N0 to N. M-1 Then the probability that the neutron's energy is in channel X is:

[0051]

[0052] The probability distribution of falling within the range [0, X] is as follows:

[0053]

[0054] Preferably, the method for obtaining the random distribution function of the time interval between neutron strikes on the detector includes:

[0055] Since nuclear events can be considered independent, at a given count rate, the number of neutrons hitting the detector per unit time follows a Poisson distribution; according to the Poisson distribution, the probability of n neutrons appearing within time ΔT is:

[0056]

[0057] in, This is the average count rate of neutrons; the time interval between neutron appearances (i.e., the pulse time interval) follows an average value of... If the exponential distribution is true, then the random distribution function of the pulse signal time interval t can be obtained from the exponential distribution as follows:

[0058]

[0059] Preferably, the method for obtaining the random position distribution function of neutrons hitting the 3He tube includes:

[0060] The method for determining the random position distribution function of neutrons hitting a 3He tube depends on the scenario being simulated. In electronics testing scenarios, the most common scenarios are uniform neutron impacts or single-point impacts by collimated neutrons. In these two cases, the random position distribution function can be directly obtained from the mathematical properties of distribution. For example, for a uniform position distribution, assuming the effective length of the 3He tube is L, the distribution function of the position l of the 3He tube in the neutron concentration is:

[0061]

[0062] For a more general probability density distribution at any location, it can be obtained by integrating the location probability density function.

[0063] Preferably, in step 2, the method for constructing the digital waveform pulses of the signals across the 3He tube includes:

[0064] The digital waveform pulses of the signals at both ends of the 3He tube are generated based on the random distribution function of the pulse amplitude, the random distribution function of the pulse signal time interval, and the random position distribution function of the neutron hitting the 3He tube. We know that uniformly distributed random numbers are easily generated in microcontrollers, FPGAs, and other digital control chips. Randomly distributed random numbers can be obtained by combining uniformly distributed random numbers with the inverse function sampling method. The inverse function sampling method is a known and mature algorithm. For example, given the random distribution function of the pulse signal amplitude as y = F(x), since the probability in the real world cannot be negative, the distribution function F(x) is always monotonically increasing. Therefore, y = F(x) must have an inverse function, meaning x can be obtained using y. Sampling the parameter x can be replaced by sampling a uniformly distributed random number y between [0,1], and then obtaining the sampled value of x through the inverse function.

[0065] For example, given the random distribution function of the total pulse amplitude, because the total pulse amplitude is not uniform, it is difficult to directly sample and make it conform to the corresponding distribution function. We can obtain a uniformly distributed 32-bit random number Y1 by sampling using the Linear Feedback Shift Register (LSFR) method in the FPGA. Then, there must exist an X1 such that:

[0066]

[0067] By setting up a lookup table in the FPGA, X1 obtained by calculating Y1 using a uniform distribution is the random number of the total pulse amplitude generated. Similarly, a similar method can be used to obtain random numbers for the nuclear pulse time interval and neutron strike location.

[0068] We know that in a single neutron hit event, the signal amplitude across the 3He tube is related to the total charge and the location of the particle impact. For example... Figure 2 As shown, under ideal conditions, assuming the effective length of the 3He tube is L, the distance from the neutron incident position to end A (left end) is X, and the resistance corresponding to the anode wire of length X is R. A The resistance of the anode wire corresponding to segment LX is R. B When a neutron is incident at position X in the 3He tube, it reacts with the 3He gas to produce protons and tritium nuclei. During their movement, the protons and tritium nuclei produce electrons. These electrons move towards the anode wire under the influence of the electric field, undergoing avalanche amplification during their movement. The charge reaching the anode wire moves towards both ends of the 3He tube in the form of pulsed currents. The two currents are in opposite directions and have magnitudes i. A (t), i B (t), is inversely proportional to the resistance of each anode wire, i.e., i A (t)=V(t) / R A i B (t)=V(t) / R B Current i A (t), i B (t) After flowing out of the 3He transistor from both the left and right ends, the currents enter the next stage of the amplifier circuit and other electronic components. Finally, the data acquisition system reads the charge values ​​R corresponding to the two currents. A R B .

[0069] Typically, the electronic systems on both sides of a 3He transistor have the same current amplification factor, i.e., Q. A =∫i A (t)dt,Q B =∫i B Then Q = ∫(t)dt. A ×R A =Q B ×R BSince the resistance of the anode wire is directly proportional to its length, the equation for the incident position is obtained by conversion:

[0070]

[0071] Simultaneously, the voltage U output by the preamplifiers at both ends A and U B Proportional to Q A and Q B Therefore, the relationship between the voltage across the terminals and the total voltage is as follows:

[0072]

[0073]

[0074] Using the above calculation formula, the amplitude of the signals at both ends of the 3He tube to be simulated can be obtained based on the amplitude distribution random number and the hit position random number. Combined with the pulse time interval random number, the digital pulse signals at both ends of the 3He tube can be simulated and synthesized respectively.

[0075] After obtaining the digital pulse signals across the 3He transistor, the signals are transmitted through two channels such as... Figure 3 The high-speed DAC circuit shown can convert digital pulses into real pulse signals for 3He readout electronics testing. The relative amplitude of the two pulses contains information about the neutron impact location, the sum of the amplitudes of the two pulses contains information about the neutron's energy, and the time interval between the pulses contains information about the neutron count rate.

[0076] The working principle of this invention is as follows: Figure 1 As shown, the first uniformly distributed random number generator combines the total pulse amplitude random distribution function and obtains amplitude random numbers through the first inverse function sampling processor. The second uniformly distributed random number generator combines the neutron-hit-detector time interval random distribution function and obtains time interval random numbers through the second inverse function sampling processor. The third uniformly distributed random number generator combines the neutron-hit-3He tube random position distribution function and obtains hit position random numbers through the third inverse function sampling processor. The amplitude random numbers, time interval random numbers, and hit position random numbers generate two digital pulse signals through digital waveform generators at both ends of the 3He tube: digital waveform at end A and digital waveform at end B. The digital waveforms at end A and end B are then converted into real pulse signals by high-speed DAC circuits to obtain real pulse signals at end A and end B.

[0077] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of generating simulated signals for a position sensitive 3He tube neutron detector, the method comprising: The method comprises the following steps: ​ Step 1, obtaining a total pulse amplitude random distribution function of single particle impact, a time interval random distribution function of neutron impact on a detector and a random position distribution function of neutron impact on a 3He tube respectively; Step 2, constructing a digital waveform pulse of signals at two ends of the 3He tube according to the total pulse amplitude random distribution function, the time interval random distribution function of neutron impact on the detector and the random position distribution function of neutron impact on the 3He tube; Step 3, converting the digital waveform pulse into real two-way pulse signal output through two-way DAC; In step 1, the total pulse amplitude random distribution function acquisition method comprises that the amount of electric charge generated after the neutron impacts on the 3He tube detector is proportional to the neutron energy, and the output pulse amplitude of the charge-sensitive preamplifier is proportional to the input electric charge amount; wherein the total pulse amplitude distribution of signals at two ends of the 3He tube detector represents the energy distribution of the neutrons, and the total pulse amplitude distribution function generated by the neutron impact on the 3He tube can be calculated according to a specific neutron energy spectrum, and the specific operation of obtaining the neutron energy distribution function according to the specific neutron energy spectrum is as follows: Assume that the neutron spectrum to be simulated is divided into M channels, 0 to (M-1), with counts N0 to N M-1 , then the probability that a neutron has an energy in channel X is: ； The probability distribution between [0, X] is: ； In step 1, the time interval random distribution function acquisition method of neutron impact on the detector comprises: Wherein, the nuclear events can be considered as independent and irrelevant, and the number of neutrons hitting the detector per unit time under a given counting rate satisfies the Poisson distribution, and the probability of n neutrons appearing in time ΔT according to the Poisson distribution is: ； wherein, is the average count rate of the neutrons, the time interval of the neutron occurrence (i.e. the time interval of the pulses) obeys an exponential distribution with an average of The random distribution function of the pulse signal time interval t can be obtained from the exponential distribution as follows: ； In step 1, the random position distribution function acquisition method of neutron impact on the 3He tube comprises: The method of neutron hitting the random position distribution function of 3He tube is related to the scene to be simulated. Generally in the scene of electronic test, the most commonly used is that the position of neutron hitting is uniformly distributed, or the collimated neutron hits single, in which case the random position distribution function can be directly obtained according to the mathematical properties of the distribution; for the uniformly distributed position distribution, assuming that the effective length of 3He tube is L, then the distribution function of the position of neutron hitting 3He tube is: ​ ； In step 2, the method for constructing the digital waveform pulse of signals at two ends of the 3He tube comprises: The pulse signal amplitude random distribution function is y=F(x), because the real-world probability cannot be negative, the distribution function F(x) is always monotonically increasing, so y=F(x) must exist an inverse function, that is, y can be used to obtain x; the sampling of the parameter x can be replaced by the sampling of the uniform distribution random number y between [0, 1], and then the sampling value of x is obtained through the inverse function; A 32-bit random number Y1 is obtained by sampling through the linear feedback shift register (LSFR) method in the FPGA, so there must be an X1 that makes: ； The look-up table is set in the FPGA, and the X1 obtained by the Y1 of the uniform distribution is the total pulse amplitude random number generated this time, and the nuclear pulse time interval random number and the neutron impact position random number are obtained by using a similar method; In single neutron hit event, the signal amplitude of 3He tube two ends is related to total charge and particle hit position, assuming 3He tube effective length is , neutron incident position distance A end is , The length of the anode wire corresponding to the resistance is , The resistance of the anode wire corresponding to this section is ; when the neutron incident to 3He tube position , the reaction with 3He gas produces proton and tritium nucleus, the proton and tritium nucleus produce electrons in the process of movement, the electrons move to the anode wire under the action of electric field, the avalanche amplification occurs in the process of movement, the charge reaches the anode wire in the form of pulse current to 3He tube two ends; two current directions are opposite, the current size is , , and the size of the resistance through the anode wire is inversely proportional, that is , ; the current , flows out of 3He tube from left and right two ends and enters the next stage of amplification circuit and other electronics, finally the data acquisition system reads out the corresponding electric quantity value of two currents , ; 3He tube left and right side of the electronics system to the same amplification of the current, namely , , then , since the anode wire resistance and length proportional relationship, conversion is obtained incident position relationship: ； At the same time, the voltage U A and U B outputted by the preamplifiers at both ends are proportional to Q A and Q B respectively, so the relationship between the voltage at both ends and the total voltage is as follows: ， ； Through the above calculation formula, the amplitude of the 3He tube signal at two ends required to be simulated can be obtained according to the amplitude distribution random number and the impact position random number, and the digital pulse signals at two ends of the 3He tube can be simulated and synthesized in combination with the pulse time interval random number.

2. A method of generating simulated signals for a position sensitive 3He tube neutron detector according to claim 1, characterized in that: After obtaining the digital pulse signals at both ends of the 3He tube, the digital pulses are converted into real pulse signals by two DAC circuits for 3He readout electronics test; the relative amplitude of the two pulses contains the information of the neutron hitting position, the sum of the amplitudes of the two pulses contains the information of the neutron energy, and the time interval of the pulses contains the information of the neutron count rate.

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