High-efficiency multichannel positron annihilation lifetime measurement method and device
By using a multi-channel valid event trigger selection method, threshold discrimination and conformity selection logic units are used to filter valid signals. Combined with FPGA and DRS4 SCA type chip for signal processing, the problem of high invalid trigger rate is solved, and efficient positron annihilation lifetime measurement is achieved.
Patent Information
- Application Number
- CN202511305597.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-12
- Publication Date
- 2025-11-28
AI Technical Summary
In existing technologies, digital waveform sampling devices suffer from a high invalid trigger rate in positron annihilation detection, resulting in low effective trigger efficiency and an inability to effectively utilize core sampling resources.
A multi-channel valid event triggering and selection method is adopted. Valid signals are screened using a threshold discrimination circuit and a conformity selection logic unit. Signal sampling and digital processing are performed using an FPGA control module, a DRS4 SCA chip, and an ADC to avoid invalid triggering.
It improves the efficiency of acquiring effective signals, reduces dead time caused by invalid triggers, and enhances the utilization efficiency of the system's core sampling resources.
Smart Images
Figure CN121028178A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the field of nuclear spectroscopy and nuclear detection, and proposes a high-efficiency multi-channel positron annihilation lifetime measurement method and device, which adopts a multi-channel effective event trigger selection mode to realize high-efficiency and high-precision digitization of effective event signals and effectively improve the utilization efficiency of core sampling resources and systems. BACKGROUND
[0002] Positron annihilation measurement technology is a non-destructive characterization method for studying the microstructure of materials, which can identify the type, size and relative concentration of defects and other characteristic information. In the traditional field of nuclear technology application, the mode of using standard nuclear instrument modules to process nuclear detector signals has been quite mature. Due to its good expansion performance, high precision and fast speed, it has been widely used in positron annihilation spectrometers. With the continuous improvement of the performance requirements of the spectrometer, the positron annihilation spectrometer tends to be digital and multi-channel, which has significant advantages in high time resolution and high flexibility. Multi-channel means simultaneous detection and processing of multiple gamma photons, multiple types of radiation or multiple events, which not only improves system efficiency, but also contains new methods. For large-scale multi-channel signal data processing, using traditional modular electronics plug-ins faces limitations such as large system integration, insufficient flexibility and high cost. Digital electronics spectrometer has the advantages of low cost, low noise and long-term stable performance, and is particularly suitable for obtaining physical characteristic information of large-scale multi-channel nuclear signals.
[0003] Currently, digital waveform sampling technology and circuits have become a hot topic in the fields of high-energy physics experiments, nuclear medicine, particle physics detection, etc. With the continuous development of advanced digital sampling technology, a variety of new high-performance digital sampling devices with high sampling rate, high bandwidth and low power consumption have been applied in various nuclear detection fields, and their performance is fully suitable for the high-speed sampling of nanosecond-level front fast-time signals of conventional positron annihilation detectors. However, since the chip cannot be sampled during data reading, there is a large dead time, which also leads to its main application in some low-count-rate positron annihilation detection scenarios. For example, if a DRS 4SCA chip is used directly for conventional positron annihilation lifetime measurement, the trigger logic will cause a large amount of invalid signal reading, resulting in a much higher probability of invalid trigger than effective trigger, so that the chip is in the dead time caused by invalid trigger for a long time, resulting in a very low detection efficiency of effective events. SUMMARY
[0004] In view of the problems in the prior art, the purpose of the present application is to provide a high-efficiency multi-channel positron annihilation lifetime measurement method and device. The present application is suitable for various advanced digital waveform sampling technologies and devices and can significantly improve the effective event acquisition efficiency, which is crucial for building a compact and efficient multi-channel positron annihilation lifetime measurement system.
[0005] The technical scheme of the present application is:
[0006] A high-efficiency multi-channel positron annihilation lifetime measurement method, comprising the following steps:
[0007] 1) A plurality of detectors are used to detect the prompt gamma photons and the positron annihilation gamma photons generated by the positrons of the target radioactive source and convert them into analog signals and send them to the sampling circuit;
[0008] 2) The sampling circuit is responsible for sampling and digitizing the analog signals generated by each detector and uploading them to the host computer;
[0009] 3) The host computer analyzes and processes the uploaded data to obtain the positron annihilation lifetime of the target radioactive source.
[0010] Preferably, the sampling circuit comprises a trigger module, a sampling module, a digitizing module and a control module; wherein
[0011] The control module is used to configure the trigger module, the sampling module and the digitizing module according to the instructions of the host computer;
[0012] The trigger module comprises a plurality of channels, each detector occupies one of the channels, each channel is provided with a threshold discrimination circuit, two comparators are provided in the threshold discrimination circuit to discriminate the signal amplitude of the input signal, wherein an upper threshold UL is provided in the first comparator and a lower threshold LL is provided in the second comparator, if the signal amplitude exceeds the upper threshold UL in the first comparator, logic 1 is output, otherwise logic 0 is output; if the signal amplitude exceeds the lower threshold LL in the second comparator, logic 1 is output, otherwise logic 0 is output; the logic signals output by the first comparators in each channel are input into the first coincidence judgment logic unit in the trigger module, and the logic signals output by the second comparators in each channel are input into the second coincidence judgment logic unit in the trigger module; if the sum of the input logic signals by the first coincidence judgment logic unit is equal to 1, it is determined that only one detector has detected a prompt gamma photon in the positron annihilation event; if the sum of the input logic signals by the second coincidence judgment logic unit is greater than or equal to 2, it is determined that a prompt gamma photon and at least one positron annihilation gamma photon have been detected; when the sum of the input logic signals by the first coincidence judgment logic unit is equal to 1 and the sum of the input logic signals by the second coincidence judgment logic unit is greater than or equal to 2, the trigger module controls the sampling module to solid-state sample the analog signals of each detector output by the trigger module;
[0013] The digitizing module is used to digitize the detector signals collected by the sampling module within a certain time window, convert them into data and upload them to the host computer.
[0014] Preferably, the host computer extracts the amplitude and time information of each detector signal, calculates, classifies and counts the positron lifetime between different detectors, and forms a positron annihilation lifetime spectrum containing a certain amount of events.
[0015] Preferably, the target radioactive source is 22 Na radioactive source, the prompt gamma photon is 1.28 MeV gamma photon, and the positron annihilation gamma photon is 0.511 MeV gamma photon.
[0016] Preferably, the upper threshold UL is the starting voltage of the photopeak energy window of the prompt gamma photon, and the lower threshold LL is the starting voltage of the photopeak energy window of the positron annihilation gamma photon.
[0017] Preferably, the control module is a field programmable gate array (FPGA), the sampling module is a DRS4 SCA type chip, and the digitizing module is an analog-to-digital converter (ADC).
[0018] Preferably, the time window is generally 100 ns.
[0019] A high-efficiency multi-channel positron annihilation lifetime measurement device, characterized in that it comprises a plurality of detectors, a sampling circuit and a host computer; wherein,
[0020] The detector is used for detecting the prompt gamma photon and the positron annihilation gamma photon generated by the positron of the target radioactive source and converting them into analog signals and sending them to the sampling circuit;
[0021] The sampling circuit is responsible for sampling and digitizing the analog signals generated by each detector and uploading them to the host computer;
[0022] The host computer is used for analyzing and processing the uploaded data to obtain the positron annihilation lifetime of the target radioactive source.
[0023] Preferably, the sampling circuit comprises a trigger module, a sampling module, a digitizing module and a control module; wherein,
[0024] The control module is used for configuring the trigger module, the sampling module and the digitizing module according to the instructions of the host computer;
[0025] The trigger module comprises multiple channels, each detector occupies one of the channels, each channel is provided with a threshold discrimination circuit, two comparators are arranged in the threshold discrimination circuit to discriminate the signal amplitude of the input signal, wherein an upper threshold UL is arranged in the first comparator, and a lower threshold LL is arranged in the second comparator, if the signal amplitude exceeds the upper threshold UL in the first comparator, logic 1 is output, otherwise logic 0 is output; if the signal amplitude exceeds the lower threshold LL in the second comparator, logic 1 is output, otherwise logic 0 is output; the logic signal output by the first comparator in each channel is input into the first coincidence judgment logic unit in the trigger module, and the logic signal output by the second comparator in each channel is input into the second coincidence judgment logic unit in the trigger module; if the sum of the input logic signals of the first coincidence judgment logic unit is equal to 1, it is determined that only one detector detects the prompt gamma photon in the positron annihilation event; if the sum of the input logic signals of the second coincidence judgment logic unit is greater than or equal to 2, it is determined that one prompt gamma photon and at least one positron annihilation gamma photon are detected; when the sum of the input logic signals of the first coincidence judgment logic unit is equal to 1 and the sum of the input logic signals of the second coincidence judgment logic unit is greater than or equal to 2, the trigger module controls the sampling module to solidify and sample the detector analog signals output by the trigger module.
[0026] The digitization module is used for digitizing the detector signals collected by the sampling module within a certain time window, converting the signals into data and uploading the data to an upper computer; the digitization module comprises a trigger module, a sampling module, a digitization module and a control module.
[0027] The advantages of the present application are as follows:
[0028] The present application can improve the collection efficiency of core signals. In the application, the effective event pre-judgment selection method is used to screen effective events, avoid the redundant triggering of the invalid event of the digitization sampling circuit, and effectively improve the utilization efficiency of the core sampling resources.
[0029] The measurement structure of the present application is simple. The present application can realize accurate measurement of positron annihilation lifetime without relying on complex and expensive nuclear electronics modular plug-ins, and can be popularized in conventional laboratories. BRIEF DESCRIPTION OF DRAWINGS
[0030] Figure 1 It is a schematic diagram of the measurement method principle.
[0031] Figure 2 It is a schematic diagram of the trigger module.
[0032] Figure 3 It is a schematic diagram of the threshold selection of the trigger module.
[0033] Figure 4 This is a measurement example diagram. Detailed Implementation
[0034] The present invention will now be described in further detail with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.
[0035] For use 22 The principle of the multi-channel high-efficiency positron annihilation lifetime measurement method designed in this invention for Na radioactive sources is as follows: Figure 1 As shown, it mainly consists of three parts: a detector, a sampling circuit, and a host computer. The detector is responsible for detecting the instantaneous 1.28 MeV gamma photons generated by positrons and the 0.511 MeV gamma photons annihilated by positrons as start and stop signals, and converting them into analog signals. The sampling circuit is responsible for sampling and digitizing the analog signals generated by each detector and uploading them in packages. The host computer is responsible for program-controlled functions and parameters of the sampling circuit, receiving data uploaded by the sampling circuit, and analyzing and processing it.
[0036] The sampling circuit mainly consists of four parts: a trigger module, a sampling module, a digitization module, and a control module. Its implementation logic is as follows: according to the program issued by the host computer's program control software, the control module configures the functions and parameters of the trigger module, the sampling module, and the digitization module respectively; when the input detector analog signal meets the setting requirements of the trigger module, the sampling module starts or stops sampling the detector signals of each channel; the digitization module digitizes the detector signals collected by the sampling module within a certain time window, converts them into data, packages them in a certain order, and uploads them to the host computer.
[0037] After the detector signal data packets are uploaded to the host computer, the data processing module further processes the detector signals according to the settings of the program control software. This includes extracting the amplitude and time information of each detector signal, calculating, classifying and statistically analyzing the positron lifetimes of different detectors, and finally forming a positron annihilation lifetime spectrum containing a certain number of statistical events.
[0038] The trigger module in the sampling circuit is key to achieving high-efficiency measurement of multi-channel positron annihilation lifetime. Its internal implementation logic is as follows: Figure 2 As shown, the system mainly includes two functions: threshold discrimination and coincidence selection. The system contains multiple detectors, each occupying one channel of the trigger module. Each signal output from the multi-channel detectors, after being input to the trigger module, undergoes amplitude discrimination by both the upper threshold (UL) and lower threshold (LL) in the threshold discrimination circuit. Figure 3As shown, the upper threshold and the lower threshold are calibrated according to the actual amplitude of the output signal of each detector, the starting voltage of the photoelectric peak energy window of the 1.28 MeV gamma photon is taken as the upper threshold, the starting voltage of the photoelectric peak energy window of the 0.511 MeV gamma photon is taken as the lower threshold, and generally the upper threshold voltage value is greater than the lower threshold voltage. When the detector signal is amplitude discriminated, if the signal amplitude exceeds the upper threshold UL or the lower threshold LL, the corresponding output is logic 1, otherwise the output is logic 0.
[0039] After the threshold discrimination of each signal by the two comparators, the logic values output by the threshold discrimination circuit are calculated and discriminated by a coincidence selection logic function to screen out the correct cases of simultaneously detecting 1.28 MeV gamma photons and 0.511 MeV gamma photons. In this function, two logic conditions need to be met simultaneously within a certain time window (usually 100 ns): (1) the sum of the output logic values of each upper threshold discrimination circuit is equal to 1, indicating that only one detector detects 1.28 MeV gamma photons in this positron annihilation event; (2) the sum of the output logic values of each lower threshold discrimination circuit is greater than or equal to 2, indicating that at least one 0.511 MeV annihilation gamma photon is detected in addition to the 1.28 MeV starting gamma photon. When the coincidence selection logic meets the above two logic conditions simultaneously, the trigger module will control the sampling module to solidify and sample each channel of the detector analog signal output by the trigger module.
[0040] Embodiment
[0041] Figure 4 For an embodiment based on the above content of the application, in the sampling circuit, a field programmable gate array FPGA is used as the control module, a DRS4 SCA type chip is used as the sampling module, and an analog to digital converter ADC is used as the digitizing module.
[0042] The method realizes the function of efficient selection of positron annihilation events, can effectively reduce the dead time introduced by false triggers to the sampling circuit, greatly improves the utilization efficiency of the core sampling resources of the positron annihilation lifetime measurement system, and is particularly suitable for greatly improving the efficiency of multi-channel positron lifetime measurement.
[0043] Although specific embodiments of the application are disclosed for illustrative purposes, the purpose is to help understand the content of the application and to implement it, and those skilled in the art can understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the application and the appended claims. Therefore, the application should not be limited to the disclosed content of the best embodiment, and the scope of protection claimed by the application is defined by the scope of the claims.
Claims
1. A high-efficiency multi-channel positron annihilation lifetime measurement method, comprising the following steps: 1) Utilize multiple detectors to detect the transient gamma photons generated by positrons in the target radiation source and the gamma photons annihilated by positrons, and convert them into analog signals to send to the sampling circuit; 2) The sampling circuit is responsible for sampling and digitizing the analog signals generated by each detector and then uploading them to the host computer; 3) The host computer analyzes and processes the uploaded data to obtain the positron annihilation lifetime of the target radioactive source.
2. The method according to claim 1, characterized in that, The sampling circuit includes a trigger module, a sampling module, a digitization module, and a control module; wherein... The control module is used to configure the trigger module, sampling module and digitization module respectively according to the instructions of the host computer; The triggering module includes multiple channels, with each detector occupying one channel. Each channel is equipped with a threshold discrimination circuit, which has two comparators to discriminate the signal amplitude of the input signal. The first comparator has an upper threshold UL, and the second comparator has a lower threshold LL. If the signal amplitude exceeds the upper threshold UL in the first comparator, it outputs logic 1; otherwise, it outputs logic 0. Similarly, if the signal amplitude exceeds the lower threshold LL in the second comparator, it outputs logic 1; otherwise, it outputs logic 0. The logic signals output by the first comparator in each channel are input to the first compliance selection logic unit in the triggering module, and the logic signals output by the second comparator in each channel are input to... The first coincidence selection logic unit adds the input logic signals to the second coincidence selection logic unit in the trigger module. If the sum of the input logic signals by the first coincidence selection logic unit equals 1, it is determined that in the positron annihilation case, only one detector detected a transient gamma photon. If the sum of the input logic signals by the second coincidence selection logic unit is greater than or equal to 2, it is determined that one transient gamma photon and at least one positron annihilation gamma photon were detected. When the sum of the input logic signals by the first coincidence selection logic unit equals 1 and the sum of the input logic signals by the second coincidence selection logic unit is greater than or equal to 2, the trigger module controls the sampling module to perform solidified sampling of the analog signals of each detector output by the trigger module. The digitization module is used to digitize the detector signals collected by the sampling module within a certain time window, convert them into data, and upload them to the host computer.
3. The method according to claim 1, characterized in that, The host computer extracts the amplitude and time information of the signals from each detector, calculates, classifies and statistically analyzes the positron lifetimes of different detectors, and forms a positron annihilation lifetime spectrum containing a certain number of statistical events.
4. The method according to claim 1, 2, or 3, characterized in that, The target radioactive source is 22 The Na radioactive source has a transient gamma photon of 1.28 MeV and a positron annihilation gamma photon of 0.511 MeV.
5. The method according to claim 1, 2, or 3, characterized in that, The upper threshold UL is the starting voltage of the transient gamma photonic photoelectric peak energy window, and the lower threshold LL is the starting voltage of the positron annihilation gamma photonic photoelectric peak energy window.
6. The method according to claim 1, 2, or 3, characterized in that, The control module is a field-programmable gate array (FPGA), the sampling module is a DRS4 SCA chip, and the digitization module is an analog-to-digital converter (ADC).
7. The method according to claim 1, 2, or 3, characterized in that, The time window is 100 ns.
8. A high-efficiency multi-channel positron annihilation lifetime measurement device, characterized in that, It includes multiple detectors, sampling circuits, and a host computer; among which, The detector is used to detect the transient gamma photons generated by the positrons of the target radiation source and the gamma photons annihilated by the positrons, and convert them into analog signals and send them to the sampling circuit. The sampling circuit is responsible for sampling and digitizing the analog signals generated by each detector and then uploading them to the host computer. The host computer is used to analyze and process the uploaded data to obtain the positron annihilation lifetime of the target radioactive source.
9. The apparatus according to claim 8, characterized in that, The sampling circuit includes a trigger module, a sampling module, a digitization module, and a control module; wherein, The control module is used to configure the trigger module, sampling module and digitization module respectively according to the instructions of the host computer; The triggering module includes multiple channels, with each detector occupying one channel. Each channel is equipped with a threshold discrimination circuit, which has two comparators to discriminate the signal amplitude of the input signal. The first comparator has an upper threshold UL, and the second comparator has a lower threshold LL. If the signal amplitude exceeds the upper threshold UL in the first comparator, it outputs logic 1; otherwise, it outputs logic 0. Similarly, if the signal amplitude exceeds the lower threshold LL in the second comparator, it outputs logic 1; otherwise, it outputs logic 0. The logic signals output by the first comparator in each channel are input to the first coincidence selection logic unit in the triggering module, and the logic signals output by the second comparator in each channel are input to the second coincidence selection logic unit in the triggering module. If the first coincidence selection logic unit determines the input logic signal... If the summation equals 1, it is determined that in the positron annihilation case, only one detector detected a transient gamma photon; if the summation of the input logic signals by the second coincidence selection logic unit is greater than or equal to 2, it is determined that one transient gamma photon and at least one positron annihilation gamma photon were detected; when the summation of the input logic signals by the first coincidence selection logic unit is equal to 1 and the summation of the input logic signals by the second coincidence selection logic unit is greater than or equal to 2, the trigger module controls the sampling module to perform solidified sampling of the analog signals of each detector output by the trigger module; the digitization module is used to digitize the detector signals solidified and collected by the sampling module within a certain time window, convert them into data, and upload them to the host computer; it includes a trigger module, a sampling module, a digitization module, and a control module.
10. The apparatus according to claim 8, characterized in that, The host computer extracts the amplitude and time information of the signals from each detector, calculates, classifies and statistically analyzes the positron lifetimes of different detectors, and forms a positron annihilation lifetime spectrum containing a certain number of statistical events.