Method and System for Measuring Positron Annihilation Lifetime Spectrum for Liquid Scintillation Characterization

Abstract

The present disclosure relates to a positron annihilation lifetime spectroscopy measurement method and system for liquid scintillation characterization, and relates to the fields of nuclear spectroscopy and nuclear detection technologies. In this method, a liquid scintillation sample is arranged on one side of a radiation source with a preset distance therebetween. The first energy signal generated by the decay of the radiation source is detected to obtain the start time, the second energy signal of the positron entering the liquid scintillation sample after being released from the radiation source is detected to obtain the coincidence time, and the third energy signal generated by the positron annihilation is detected to obtain the stop time. When the start time and the coincidence time meet the preset coincidence selection conditions, the positron annihilation lifetime spectrum is statistically analyzed according to the start time and the stop time. This method does not require the setting of window materials and can flexibly adjust the measurement environment. The coincidence time measured by the liquid scintillation flash is not involved in the statistics, avoiding the influence of the liquid scintillation performance on the accuracy of the measurement results. Instead, the screened start time and stop time are used for statistics, which can exclude error cases and ensure accurate, flexible, and stable measurement.

Description

Background Art

[0002] Liquid scintillation, also known as liquid scintillator, is an organic solution, usually composed of a scintillating organic solvent and a luminescent substance, and sometimes other dopants are added according to actual application requirements. When the energy conversion of particle rays occurs inside the liquid scintillation, fluorescent photons corresponding to the spectrum can be emitted. Therefore, by collecting and detecting the fluorescent photons in the backend electronics, the detection and discrimination of particle rays can be achieved. Among them, particle rays can include charged particles, gamma photons, neutrons, etc. The performance of liquid scintillation is usually related to its microstructure. In applications, the microstructure of liquid scintillation may change due to factors such as physical components, ionic chemical environment, and aging, which may lead to changes in its macroscopic properties, such as optical properties, and further affect its detection and discrimination effects on particle rays. Since the change in the microstructure of a substance occurs earlier than the change in macroscopic properties, the effective characterization of the microstructure of liquid scintillation plays an important role in monitoring the change in the macroscopic properties of liquid scintillation.

[0003] Positron Annihilation Lifetime Spectrum (PALS) measurement can characterize the microstructure of a sample by measuring the probability of positrons annihilating with electrons in the sample per unit time. Usually, different annihilation lifetimes can characterize the types of defects in the microstructure, and the intensities of different annihilation lifetimes can characterize the number of defects in the microstructure. PALS is an effective means for non-destructively characterizing the microstructure of a sample at the atomic scale. Usually, 22 positrons are produced by the decay of a 22 Na radiation source, and then 22 the 1.28 MeV gamma photons cascaded when the 22 Na radiation source produces positrons, and the 0.511 MeV gamma photons produced after the positrons annihilate in the sample are detected, and then the positron annihilation lifetime spectrum is obtained according to the detection time difference.

[0004] Positrons can form positronium (Ps) with electrons in the liquid scintillation, including p-Ps (para-positronium, para-electronium) and o-Ps (ortho-positronium, ortho-electronium). Ps can interact with atoms, ions, and molecular groups in the liquid scintillation, and thus annihilate. Therefore, the change in the microstructure of the liquid scintillation can be characterized by measuring the annihilation lifetime and its intensity of Ps in the liquid scintillation. In PALS, the radiation source-sample usually adopts a "sandwich" structure setting, with two identical samples closely attached to both sides of the radiation source, so as to ensure that all the positrons generated by the radiation source around are annihilated in the samples. However, liquid scintillation is viscous, and direct contact with the radiation source will cause contamination or corrosion to it.

[0005] At present, in the application of using PALS to characterize liquid scintillators, window materials are usually used to seal the radiation source or to seal the liquid scintillator sample to avoid direct contact between the radiation source and the liquid scintillator. For example, a titanium (Ti) film can be used to seal the radiation source, and then the sealed radiation source is placed into the liquid scintillator sample. Or, a polyimide (PI) film can also be used to seal the openings of two containers containing liquid scintillator samples, and then the radiation source is placed between the two containers and set close to the PI film respectively. Alternatively, the radiation source and the sample can be separated. The energy signal generated by the thermalization of positrons in the liquid scintillator sample is used as the start signal, and the energy signal generated after the annihilation of positrons is used as the stop signal.

[0006] In the above solutions, when the sample and the radiation source are set close to each other, sufficient window materials are required to avoid contact between the radiation source and the liquid scintillator, making the measurement structure complex and the operation inconvenient. In particular, it is difficult to replace the sample, and the annihilation component of positrons in the window material cannot be removed, resulting in poor accuracy of the annihilation lifetime measurement. In addition, close contact also makes it difficult to adjust the test conditions and atmosphere environment of the liquid scintillator sample during the measurement, making the applicability and flexibility of using PALS to characterize the liquid scintillator poor. When the radiation source and the sample are separated, the gamma photons generated when the radiation source generates positrons and the gamma photons generated when positrons annihilate in non-liquid scintillator samples and enter the liquid scintillator sample will also be recorded, and it is impossible to avoid introducing error events during the measurement, resulting in poor measurement accuracy. In addition, the acquisition of the start signal in this method is easily affected by the performance of the liquid scintillator sample, and the stability is poor.

[0007] It should be noted that the information disclosed in the above background art section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0008] The purpose of the present disclosure is to provide a positron annihilation lifetime spectrum measurement method and system for liquid scintillator characterization. When using PLAS for liquid scintillator characterization, it can effectively screen error events, ensure measurement stability, avoid the use of window materials, and do not require close contact between the radiation source and the sample. The test conditions, atmosphere environment, etc. of the liquid scintillator sample can be adjusted according to the measurement requirements, improving the accuracy, applicability and flexibility of the measurement.

[0009] According to the first aspect of the present disclosure, a positron annihilation lifetime spectrum measurement method for liquid scintillator characterization is provided. The method may include:

[0010] Detecting the first energy signal generated by the decay of the radiation source to obtain the start time. The energy threshold of the first energy signal is set according to the energy of the start gamma photon, and the start gamma photon is generated by the decay of the radiation source;

[0011] Detecting the second energy signal of the positron to obtain the coincidence time. The positron is released by the radiation source and enters the liquid scintillation sample. The energy threshold of the second energy signal is set according to the electronic noise. The liquid scintillation sample is arranged on one side of the radiation source and separated from the radiation source by a preset distance;

[0012] Detecting the third energy signal generated by positron annihilation to obtain the stop time. The energy threshold of the third energy signal is set according to the energy of the annihilation gamma photon, and the annihilation gamma photon is generated by positron annihilation;

[0013] When the start time and the coincidence time meet the preset coincidence selection conditions, the positron annihilation lifetime spectrum of the liquid scintillation sample is statistically analyzed according to the start time and the stop time.

[0014] Optionally, the preset coincidence selection conditions include that the start time and the coincidence time are obtained within the first time window.

[0015] Optionally, the first time window is less than 1 nanosecond.

[0016] Optionally, when the start time and the coincidence time meet the preset coincidence selection conditions, the positron annihilation lifetime spectrum of the liquid scintillation sample is statistically analyzed according to the start time and the stop time, including:

[0017] When the start time and the coincidence time meet the preset coincidence selection conditions, and the start time and the stop time are obtained within the second time window, the positron annihilation lifetime spectrum of the liquid scintillation sample is statistically analyzed according to the start time and the stop time. The second time window is set according to the annihilation lifetime of the positron in the liquid scintillation sample.

[0018] According to the second aspect of the present disclosure, there is provided a positron annihilation lifetime spectrum measurement system for liquid scintillation characterization. The system may include:

[0019] A start detection module, configured to detect the first energy signal generated by the decay of the radiation source to obtain the start time. The energy threshold of the first energy signal is set according to the energy of the start gamma photon, and the start gamma photon is generated by the decay of the radiation source;

[0020] A coincidence detection module, configured to detect the second energy signal of the positron to obtain the coincidence time. The positron is released by the radiation source and enters the liquid scintillation sample. The energy threshold of the second energy signal is set according to the electronic noise. The liquid scintillation sample is arranged on one side of the radiation source and separated from the radiation source by a preset distance;

[0021] A stop detection module, configured to detect the third energy signal generated by positron annihilation to obtain the stop time. The energy threshold of the third energy signal is set according to the energy of the annihilation gamma photon, and the annihilation gamma photon is generated by positron annihilation;

[0022] A data statistics module, configured to, when the start time and the coincidence time meet the preset coincidence selection conditions, statistically analyze the positron annihilation lifetime spectrum of the liquid scintillation sample according to the start time and the stop time.

[0023] Optionally, the data statistics module includes:

[0024] A coincidence selection unit, configured to output a trigger signal when the start time and the coincidence time meet the preset coincidence selection conditions, where the preset coincidence selection conditions include that the start time and the coincidence time are obtained within a first time window;

[0025] A time difference calculation unit, configured to calculate the positron annihilation lifetime according to the start time and the stop time when receiving the trigger signal;

[0026] A lifetime spectrum statistics unit, configured to statistically analyze the positron annihilation lifetime spectrum of the liquid scintillation sample according to the obtained positron annihilation lifetime.

[0027] Optionally, the first time window is less than 1 nanosecond.

[0028] Optionally, the data statistics module is specifically configured to, when the start time and the coincidence time meet the preset coincidence selection conditions, and the start time and the stop time are obtained within a second time window, statistically analyze the positron annihilation lifetime spectrum of the liquid scintillation sample according to the start time and the stop time, where the second time window is set according to the annihilation lifetime of positrons in the liquid scintillation sample.

[0029] Optionally, the start detection module includes:

[0030] A start detector, configured to detect a first energy signal generated by the decay of a radiation source;

[0031] A first time extraction unit, configured to extract the occurrence time of the first energy signal to obtain the start time when the first energy signal reaches 1.28 MeV;

[0032] Optionally, the stop detection module includes:

[0033] A stop detector, configured to detect a third energy signal generated by positron annihilation;

[0034] A second time extraction unit, configured to extract the occurrence time of the third energy signal to obtain the stop time when the third energy signal reaches 0.511 MeV.

[0035] Optionally, the start detector and the stop detector are scintillation detectors.

[0036] According to the third aspect of the present disclosure, there is provided a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the method of the first aspect is implemented.

[0037] According to a fourth aspect of the present disclosure, there is provided an electronic device, including:

[0038] a processor; and

[0039] a memory for storing executable instructions of the processor;

[0040] wherein, the processor is configured to execute the method of the first aspect above via the executable instructions.

[0041] In an embodiment of the present disclosure, the liquid scintillation sample is arranged on one side of the radiation source and separated from the radiation source by a preset distance. On this basis, the first energy signal generated by the decay of the radiation source is detected respectively to obtain the start time, and the energy threshold of the first energy signal is set according to the energy of the initial gamma photon, which is generated by the decay of the radiation source; the second energy signal of the positron is detected to obtain the coincidence time, the positron is generated by the decay of the radiation source and enters the liquid scintillation sample, and the energy threshold of the second energy signal is set according to the electronic noise; the third energy signal generated by the positron annihilation is detected to obtain the stop time, and the energy threshold of the third energy signal is set according to the energy of the annihilation gamma photon, which is generated by the positron annihilation; and when the start time and the coincidence time meet the preset coincidence selection conditions, the positron annihilation lifetime spectrum of the liquid scintillation sample is statistically analyzed according to the start time and the stop time.

[0042] Since the radiation source and the liquid scintillation sample are not in close contact in the present disclosure, therefore, there is no need to additionally set a window material to isolate the radiation source and the liquid scintillation sample, thus avoiding the problem of low measurement accuracy caused by the difficult removal of the annihilation component of the positron in the window material; moreover, the test conditions, atmosphere environment, etc. of the liquid scintillation sample can be adjusted without affecting the radiation source, expanding the applicability and flexibility of using PALS for liquid scintillation characterization. Further, in the present disclosure, the coincidence time measured according to the positron entering the liquid scintillation sample is not involved in the data statistics, avoiding the influence of the performance of the liquid scintillation sample on the measurement result accuracy and ensuring the stability of the measurement; and since the positron and the initial gamma photon are generated almost simultaneously, and the thermalization time of the positron after entering the liquid scintillation sample is extremely short, and the generation of the annihilation gamma photon has an obvious lag, therefore, according to the preset coincidence selection conditions, the coincidence time and the start time are subjected to coincidence selection, which can exclude the wrong events introduced by the annihilation gamma photon generated outside the liquid scintillation sample entering the liquid scintillation sample; at the same time, the start time after screening is used for statistics, which can exclude the wrong events introduced by the positron not entering the liquid scintillation sample while the initial gamma photon enters the liquid scintillation sample, effectively improving the measurement accuracy.

[0043] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings here are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present disclosure, and are used together with the specification to explain the principles of the present disclosure. Obviously, the accompanying drawings in the following description are only some embodiments of the present disclosure. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0045] Figure 1 A schematic flow chart of a positron annihilation lifetime spectrum measurement method for liquid scintillation characterization according to an embodiment of the present disclosure is illustrated.

[0046] Figure 2 A schematic flow chart of one of the coincidence selection processes according to an embodiment of the present disclosure is illustrated.

[0047] Figure 3 A schematic flow chart of another coincidence selection process according to an embodiment of the present disclosure is illustrated.

[0048] Figure 4 A schematic diagram of dead time in a coincidence selection process according to an embodiment of the present disclosure is illustrated.

[0049] Figure 5 A schematic flow chart of a process for statistically analyzing a positron annihilation lifetime spectrum according to an embodiment of the present disclosure is illustrated.

[0050] Figure 6 A schematic structural diagram of a positron annihilation lifetime spectrum measurement system for liquid scintillation characterization according to an embodiment of the present disclosure is illustrated.

[0051] Figure 7 A schematic structural diagram of another positron annihilation lifetime spectrum measurement system for liquid scintillation characterization according to an embodiment of the present disclosure is illustrated.

[0052] Figure 8 A schematic structural diagram of an electronic device according to an embodiment of the present disclosure is illustrated. Detailed implementation manners

[0053] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the example embodiments to those skilled in the art. The features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of the embodiments of this disclosure. However, those skilled in the art will realize that the technical solutions of this disclosure may be practiced without one or more of the specific details, or other methods, components, devices, steps, etc. may be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring aspects of this disclosure.

[0054] In addition, the accompanying drawings are only schematic illustrations of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0055] In an embodiment of this disclosure, a method for measuring positron annihilation lifetime spectrum for liquid scintillation characterization is provided. By setting a liquid scintillation sample at a preset distance on one side of a radiation source, a first energy signal from the decay of the radiation source is respectively detected to obtain a start time, and the energy threshold of the first energy signal is set according to the energy of the initial gamma photon; a second energy signal of a positron is detected to obtain a coincidence time, the positron is generated by the decay of the radiation source and enters the liquid scintillation sample, and the energy threshold of the second energy signal is set according to the electronic noise; a third energy signal generated by positron annihilation is detected to obtain a stop time, and the energy threshold of the third energy signal is set according to the energy of the annihilation gamma photon, the annihilation gamma photon is generated by positron annihilation; and the start time is screened using the coincidence time, and then the positron annihilation lifetime spectrum of the liquid scintillation sample is statistically analyzed based on the start time and the stop time. Without the need to set a window material, the test conditions, atmosphere environment, etc. of the liquid scintillation sample can be adjusted, thereby improving the accuracy, applicability, and flexibility of the measurement; the coincidence time is used to screen the positron annihilation events, and the coincidence time does not participate in the statistical analysis of the positron annihilation lifetime spectrum, improving the correctness and stability of the measurement.

[0056] The embodiments of this disclosure will be described in detail below with reference to the accompanying drawings.

[0057] Figure 1The flowchart of a positron annihilation lifetime spectrum measurement method for liquid scintillation characterization in an embodiment of the present disclosure is exemplified. This method is applied to a positron annihilation lifetime spectrum measurement system for liquid scintillation characterization, and this device can be integrated on an electronic device, such as a notebook, a desktop computer, etc. This method includes the following steps 110 to 140.

[0058] Step 110: Detect the first energy signal generated by the decay of the radiation source to obtain the start time. The energy threshold of the first energy signal is set according to the energy of the initial gamma photon, and the initial gamma photon is generated by the decay of the radiation source.

[0059] Among them, the measurement of the positron annihilation lifetime spectrum is usually based on the β + decay of radioactive isotopes to generate positrons. In the measurement, 22 Na is often used as the radiation source. 22 Na can release positrons with kinetic energy ranging from 0 to 0.545 MeV. When the radiation source decays to generate positrons, initial gamma photons will be cascaded. Therefore, the time when the initial gamma photons are generated can be used as the start time of the positrons generated by the decay of the radiation source. Since the initial gamma photons released by the decay of the radiation source have a specific energy, such as 22 Na cascades to generate 1.28 MeV initial gamma photons when releasing positrons. Therefore, the corresponding energy threshold can be set according to this specific energy, and the occurrence time when the detected first energy signal reaches this energy threshold is used as the generation time of the positrons to obtain the start time.

[0060] Step 120: Detect the second energy signal of the positrons to obtain the coincidence time. The positrons are released by the radiation source and enter the liquid scintillation sample. The energy threshold of the second energy signal is set according to the electronic noise. The liquid scintillation sample is arranged on one side of the radiation source and is separated from the radiation source by a preset distance.

[0061] In the embodiment of the present disclosure, the liquid scintillation sample can be arranged on one side of the radiation source, at a preset distance from the radiation source. Thus, the radiation source and the liquid scintillation sample are separated, which can effectively prevent the radiation source from being corroded and polluted by the liquid scintillation sample, and can also adjust the test conditions, atmosphere environment, etc. of the liquid scintillation sample without affecting the radiation source, such as measuring under different temperature conditions. The preset distance can be set according to the height of the liquid scintillation sample, the type of radiation source, the requirements of test conditions, etc. The present disclosure does not make specific limitations on this.

[0062] Among them, after the positrons enter the liquid scintillation sample, they usually go through two processes: thermalization and annihilation. During the thermalization process, the positrons in the liquid scintillation sample undergo a series of elastic collisions with atoms and molecules, and their energy rapidly dissipates to the thermal motion energy, that is, <1eV. The second energy signal can be the electrical signal obtained by converting the optical signal generated by scintillation after the positrons enter the liquid scintillation sample through a coincidence detector formed by coupling the liquid scintillation sample with a photomultiplier tube (PMT). Also, since the intensity of the optical signal generated during the scintillation process of the liquid scintillation sample is related to the energy of the positrons, the amplitude of the second energy signal is also related to the energy of the positrons. Therefore, it is possible to detect whether the positrons enter the liquid scintillation sample based on the amplitude of the second energy signal, and extract the occurrence time of the second energy signal to obtain the coincidence time.

[0063] However, on the one hand, since the liquid scintillation sample in the present disclosure is only arranged on one side of the radiation source and separated by a preset distance, and the radiation source generates positrons in random directions, some positrons may annihilate outside the liquid scintillation sample, resulting in a reduction in the effective count; on the other hand, since the energy distribution range of the positrons released by the radiation source is relatively wide, for example 22 When 22 Na is used as the radiation source, it can release positrons with kinetic energy in the range of 0 - 0.545 MeV, making the energy range released during the thermalization process of the positrons relatively wide. Therefore, in order to ensure the detection efficiency of the energy signal of the positrons in the liquid scintillation sample, the energy threshold can be set according to the electronic noise. Electronic noise refers to the signal generated by the statistical fluctuation of the total charge of electrons during their movement, usually generated by the measuring device itself, and will be superimposed on the required signal in statistics, reducing the actual measurement accuracy. In the present disclosure, the energy threshold is set according to the electronic noise of the measuring device, and all the energy signals in the energy signals generated by the liquid scintillation that are not electronic noise are collected, so that after only excluding the noise interference, the second energy signal in the liquid scintillation sample can be efficiently detected, avoiding counting omissions.

[0064] Step 130: Detect the third energy signal generated by positron annihilation to obtain the stop time. The energy threshold of the third energy signal is set according to the energy of the annihilation gamma photons, and the annihilation gamma photons are generated by positron annihilation.

[0065] Among them, since the annihilation gamma photons generated after positron annihilation have a specific energy, usually 0.511 MeV, therefore, the energy threshold can be set according to the energy of the annihilation gamma photons, and the occurrence time when the detected third energy signal reaches this energy threshold is used as the generation time of the annihilation gamma photons, obtaining the stop time of positron annihilation. Since the radiation source generates positrons in random directions, annihilation gamma photons may be released both inside and outside the liquid scintillation sample. Therefore, the stop time obtained from the third energy signal includes the annihilation events of positrons both inside and outside the liquid scintillation sample.

[0066] In the embodiments of the present disclosure, the energy thresholds of the foregoing first energy signal, second energy signal, and third energy signal can be set as upper limit thresholds, lower limit thresholds, range thresholds, etc. according to corresponding requirements. In practical applications, the forms of the energy thresholds corresponding to different energy signals can be adaptively set according to the types of devices for detecting energy signals, device specifications, measurement conditions, etc. The present disclosure does not make specific limitations thereto.

[0067] Step 140: When the start time and coincidence time meet the preset coincidence selection conditions, count the positron annihilation lifetime spectrum of the liquid scintillation sample according to the start time and stop time.

[0068] Among them, in step 120, other sources of particles, such as annihilation gamma photons generated by the annihilation of positrons outside the liquid scintillation sample, and start gamma photons cascaded during the process of the radiation source releasing positrons, may also enter the liquid scintillation sample and accumulate, thereby generating a second energy signal to cause counting and introducing error cases into the data. Since the thermalization process of positrons in the liquid scintillation sample is extremely short, usually within a few picoseconds, it can be considered that the entry of positrons into the liquid scintillation sample and the generation of start gamma photons occur almost simultaneously, while the generation of annihilation gamma photons lags due to the annihilation lifetime of positrons. Therefore, by performing coincidence selection on the start time and coincidence time according to the preset coincidence selection conditions, the coincidence cases of the start time and coincidence time are screened out, and the interference caused by the signal of the annihilation gamma photons can be avoided. In addition, when the start time and coincidence time do not meet the coincidence selection conditions, it can directly enter the coincidence selection of the next case, or further determine this case as an error case, mark or discard the data.

[0069] In the embodiments of the present disclosure, the screened start time indicates the generation time of the start gamma photon corresponding to the positron entering the liquid scintillation sample, and the stop time corresponding to the start time indicates the generation time of the annihilation gamma photon corresponding to the positron entering the liquid scintillation sample. On this basis, since the entry of positrons into the liquid scintillation sample and the generation of start gamma photons occur almost simultaneously, the screened start time and its corresponding stop time can be used to count the positron annihilation lifetime spectrum, thereby effectively avoiding the counting caused by the start gamma photons cascaded by positrons that do not enter the liquid scintillation sample or the annihilation gamma photons generated by the annihilation outside the liquid scintillation sample entering the liquid scintillation sample to generate a second energy signal; it also avoids the counting caused by the third energy signal generated by the annihilation of positrons outside the liquid scintillation sample; moreover, in the measurement of the start time and stop time, it is not necessary to utilize the luminescence characteristics of the liquid scintillation sample, so its time resolution is independent of the performance of the liquid scintillation sample, and the coincidence time that is easily affected by the performance of the liquid scintillation sample is only used for coincidence selection with the start time, ensuring the stability of the time resolution during the measurement of different liquid scintillation samples.

[0070] In an embodiment of the present disclosure, the preset coincidence selection conditions include:

[0071] The start time and the coincidence time are obtained within the first time window.

[0072] Among them, the preset coincidence selection condition can be that the start time and the coincidence time are obtained within the first time window. Since the time required for the thermalization process of positrons in the liquid scintillator sample is usually short, the time difference between the first energy signal and the second energy signal corresponding to the detected positrons is short. Therefore, the time difference between the obtained start time and coincidence time can characterize whether the positrons released by the radiation source enter the liquid scintillator sample, so the preset coincidence selection condition can be that the start time and the coincidence time are obtained within the first time window. When the start time and the coincidence time meet the preset coincidence selection condition, it means that in this instance, the positrons generated by the radiation source at the start time enter the liquid scintillator sample at the coincidence time; when the start time and the coincidence time do not meet the preset coincidence selection condition, it means that the positrons generated by the radiation source in this instance do not enter the liquid scintillator sample. In addition, since the time required for the thermalization process of positrons in the liquid scintillator sample is usually less than the annihilation lifetime of positrons, and the annihilation lifetime of positrons is usually distributed within a certain range, therefore, the size of the first time window can also be set according to the annihilation lifetime of positrons, so as to screen the start time and the coincidence time, and reduce the count caused by the annihilation gamma photons generated after the positron annihilation.

[0073] In the embodiments of the present disclosure, whether the start time and the coincidence time meet the preset coincidence selection condition can trigger timing when any one of the signals of the start time and the coincidence time is obtained, and determine that the preset coincidence selection condition is met when the other signal of the start time and the coincidence time is obtained within the first time window, otherwise it is not met; or, it can also be to continuously collect the start time and the coincidence time, and then judge whether the start time and the coincidence time are obtained within the first time window. The present disclosure does not make specific limitations on this.

[0074] Figure 2 One of the flow diagrams of a coincidence selection example of the embodiments of the present disclosure is shown in Figure 2 As shown, timing is triggered when signal 1 is obtained, and when signal 2 is obtained within the first time window, signal 1 and signal 2 meet the preset coincidence selection condition;

[0075] Or, it can also be to continuously collect signal 1 and signal 2, and count that the time difference between signal 1 and signal 2 is less than or equal to the first time window, then signal 1 and signal 2 meet the preset coincidence selection condition;

[0076] Among them, signal 1 and signal 2 can be the signals of the start time and the coincidence time respectively. When signal 1 is the start time, signal 2 is the coincidence time; when signal 1 is the coincidence time, signal 2 is the start time.

[0077] Figure 3 Schematic diagram II of a coincidence selection process according to an embodiment of the present disclosure is illustrated. As Figure 3 shown, as Figure 3 shown, when signal 1 is obtained, timing is triggered. If signal 3 is not obtained within the first time window of the timing, then signal 1 and signal 3 do not meet the preset coincidence selection conditions;

[0078] Alternatively, if signals 1 and 3 are continuously obtained and the time difference between signals 1 and 3 is statistically greater than the first time window, then signals 1 and 3 do not meet the preset coincidence selection conditions;

[0079] Among them, signals 1 and 3 can be signals of the start time and the coincidence time respectively. When signal 1 is the start time, signal 3 is the coincidence time; when signal 1 is the coincidence time, signal 3 is the start time.

[0080] In an embodiment of the present disclosure, the first time window is less than 1 nanosecond.

[0081] Among them, due to the high detection efficiency of liquid scintillation samples for positrons, almost all positrons entering the liquid scintillation samples can be detected, resulting in a relatively large number of second energy signals in practical applications, and thus a relatively large number of coincidence times are output. In the measurement of positron annihilation lifetime spectra, an invalid event can be a counting event in which any one of the start time and the coincidence time is obtained and the other signal is not obtained within the entire first time window. Therefore, when a relatively large number of coincidence times are output, it waits idle throughout the first time window, and the dead time for screening out invalid events is the entire first time window. The length of the dead time actually affects the efficiency of coincidence selection for the start time and the coincidence time. When the dead time is too long, during the coincidence selection process of the start time and the coincidence time of this event, it may cause the loss of valid events, resulting in a low detection counting rate of the positron annihilation lifetime spectrum.

[0082] In the embodiment of the present disclosure, based on forming a screening for the start time and the coincidence time within the first time window, the first time window can be set very small, thereby shortening the length of the dead time in coincidence selection. Optionally, the first time window can be set within a range less than 1 nanosecond, so that the first time window is at the picosecond level, thereby enabling the coincidence selection of invalid events to be quickly skipped to shorten the dead time. At this time, using a very small first time window can effectively avoid the problem of low counting rate caused by too long dead time in invalid events while ensuring accurate coincidence selection of the start time and the coincidence time, thereby improving the efficiency of coincidence selection for the start time and the coincidence time.

[0083] Figure 4 Schematic diagram of the dead time in a coincidence selection process according to an embodiment of the present disclosure is illustrated. As Figure 4As shown, when triggering the counter in the case of obtaining signal 1, when signal 1 is the starting time, the signal of the starting time is no longer counted before obtaining signal 2 corresponding to the time. When signal 2 is not obtained within the first preset time window, the dead time in this counting is the entire first time window. Thus, setting the first time window to be less than 1 nanosecond can effectively improve the counting efficiency.

[0084] Figure 5 The flowchart of a method for statistically analyzing the positron annihilation lifetime spectrum in an embodiment of the present disclosure is exemplified. In an embodiment of the present disclosure, as Figure 5 shown, step 140 specifically includes the following step 541.

[0085] Step 541: When the starting time and the coincidence time meet the preset coincidence selection conditions, and the starting time and the stopping time are obtained within the second time window, the positron annihilation lifetime spectrum of the liquid scintillation sample is statistically analyzed according to the starting time and the stopping time. The second time window is set according to the annihilation lifetime of positrons in the liquid scintillation sample.

[0086] Among them, on the basis that the starting time and the coincidence time meet the preset coincidence selection conditions, it is also possible to judge whether the starting time and the stopping time meet the second time window. The second time window can be set according to the annihilation lifetime of positrons in the liquid scintillation sample to further verify whether the starting time and the stopping time conform to the positron annihilation event in the liquid scintillation sample. According to the annihilation lifetime of positrons in the liquid scintillation sample, the second time window can usually be set between 50 nanoseconds and 100 nanoseconds.

[0087] In the embodiment of the present disclosure, the liquid scintillation sample is arranged on one side of the radiation source and separated from the radiation source by a preset distance. On this basis, the first energy signal generated by the decay of the radiation source is detected respectively to obtain the starting time. The energy threshold of the first energy signal is set according to the energy of the initial gamma photon, which is generated by the decay of the radiation source; the second energy signal of the positron is detected to obtain the coincidence time. The positron is generated by the decay of the radiation source and enters the liquid scintillation sample. The energy threshold of the second energy signal is set according to the electronic noise; the third energy signal generated by the positron annihilation is detected to obtain the stopping time. The energy threshold of the third energy signal is set according to the energy of the annihilation gamma photon, which is generated by the positron annihilation; and when the starting time and the coincidence time meet the preset coincidence selection conditions, the positron annihilation lifetime spectrum of the liquid scintillation sample is statistically analyzed according to the starting time and the stopping time.

[0088] Since the radiation source and the liquid scintillation sample in the present disclosure are not in close contact, there is no need to additionally set a window material to isolate the radiation source and the liquid scintillation sample, thus avoiding the problem of low measurement accuracy caused by the difficulty in removing the annihilation component of positrons in the window material. Moreover, the test conditions, atmosphere environment, etc. of the liquid scintillation sample can be adjusted without affecting the radiation source, expanding the applicability and flexibility of using PALS for liquid scintillation characterization. Further, in the present disclosure, the coincidence time measured according to the positrons entering the liquid scintillation sample is not involved in data statistics, avoiding the influence of the performance of the liquid scintillation sample on the measurement result accuracy and ensuring the stability of the measurement. Since positrons and the initial gamma photons are generated almost simultaneously, and the thermalization time of positrons after entering the liquid scintillation sample is extremely short, and the generation of annihilation gamma photons has an obvious lag, therefore, according to the preset coincidence selection conditions, coincidence selection is performed on the coincidence time and the start time, which can exclude the wrong events introduced by the annihilation gamma photons generated outside the liquid scintillation sample entering the liquid scintillation sample. At the same time, using the screened start time for statistics can exclude the wrong events introduced by the initial gamma photons entering the liquid scintillation sample while the positrons do not enter the liquid scintillation sample, effectively improving the measurement accuracy.

[0089] The following is an example of the system embodiment of the present disclosure, which can be used to execute the method embodiment of the present disclosure. For the details not disclosed in the device system example of the present disclosure, please refer to the method embodiment of the present disclosure.

[0090] Figure 6 FIG. 1 schematically shows one of the structures of a positron annihilation lifetime spectroscopy measurement system 600 for liquid scintillation characterization in an embodiment of the present disclosure. Figure 6 As shown in FIG. 1, the system may include:

[0091] An initial detection module 610, configured to detect a first energy signal generated by the decay of a radiation source to obtain an initial time, and the energy threshold of the first energy signal is set according to the energy of the initial gamma photons, and the initial gamma photons are generated by the decay of the radiation source;

[0092] A coincidence detection module 620, configured to detect a second energy signal of positrons to obtain a coincidence time, the positrons are released by the radiation source and enter the liquid scintillation sample, the energy threshold of the second energy signal is set according to the electronic noise, the liquid scintillation sample is arranged on one side of the radiation source and is separated from the radiation source by a preset distance;

[0093] A stop detection module 630, configured to detect a third energy signal generated by the annihilation of positrons to obtain a stop time, the energy threshold of the third energy signal is set according to the energy of the annihilation gamma photons, and the annihilation gamma photons are generated by the annihilation of positrons;

[0094] A data statistics module 640, configured to statistically analyze the positron annihilation lifetime spectrum of the liquid scintillation sample according to the initial time and the stop time when the initial time and the coincidence time meet the preset coincidence selection conditions.

[0095] In the embodiments of the present disclosure, a liquid scintillation sample is arranged on one side of a radiation source and separated from the radiation source by a preset distance. On this basis, a first energy signal generated by the decay of the radiation source is detected respectively to obtain a start time, and the energy threshold of the first energy signal is set according to the energy of an initial gamma photon, which is generated by the decay of the radiation source; a second energy signal of a positron is detected to obtain a coincidence time, the positron is generated by the decay of the radiation source and enters the liquid scintillation sample, and the energy threshold of the second energy signal is set according to electronic noise; a third energy signal generated by positron annihilation is detected to obtain a stop time, and the energy threshold of the third energy signal is set according to the energy of an annihilation gamma photon, which is generated by positron annihilation; and when the start time and the coincidence time meet a preset coincidence selection condition, the positron annihilation lifetime spectrum of the liquid scintillation sample is statistically analyzed according to the start time and the stop time.

[0096] Since the radiation source and the liquid scintillation sample in the present disclosure are not in close contact, there is no need to additionally arrange a window material to isolate the radiation source and the liquid scintillation sample, thereby avoiding the problem of low measurement accuracy caused by the difficult removal of the annihilation component of positrons in the window material; moreover, the test conditions, atmosphere environment, etc. of the liquid scintillation sample can be adjusted without affecting the radiation source, expanding the applicability and flexibility of using PALS for liquid scintillation characterization. Further, in the present disclosure, the coincidence time measured according to the positrons entering the liquid scintillation sample is not involved in data statistics, avoiding the influence of the performance of the liquid scintillation sample on the measurement result accuracy and ensuring the stability of the measurement; and since positrons and initial gamma photons are generated almost simultaneously, and the thermalization time of positrons after entering the liquid scintillation sample is extremely short, and the generation of annihilation gamma photons has an obvious lag, therefore, according to the preset coincidence selection condition, the coincidence time and the start time are subjected to coincidence selection, which can exclude the wrong events introduced by the annihilation gamma photons generated outside the liquid scintillation sample entering the liquid scintillation sample; at the same time, using the screened start time for statistics can exclude the wrong events introduced by the initial gamma photons entering the liquid scintillation sample while the positrons do not enter the liquid scintillation sample, effectively improving the measurement accuracy.

[0097] Figure 7 FIG. 2 shows a second schematic structural diagram of a positron annihilation lifetime spectrum measurement system 700 for liquid scintillation characterization in the embodiments of the present disclosure. As Figure 7 shown, the system may include: a start detection module 710, a coincidence detection module 720, a stop detection module 730, and a data statistics module 740;

[0098] Optionally, the data statistics module 740 includes:

[0099] A coincidence discrimination unit 7401, configured to output a trigger signal when a start time and a coincidence time meet a preset coincidence discrimination condition, where the preset coincidence discrimination condition includes that the start time and the coincidence time are obtained within a first time window;

[0100] A time difference calculation unit 7402, configured to calculate a positron annihilation lifetime according to a start time and a stop time when receiving the trigger signal;

[0101] A lifetime spectrum statistics unit 7403, configured to statistically obtain a positron annihilation lifetime spectrum of a liquid scintillation sample according to the positron annihilation lifetime.

[0102] Optionally, the start detection module 710 includes:

[0103] A start detector 7101, configured to detect a first energy signal generated by decay of the radiation source;

[0104] A first time extraction unit 7102, configured to extract the occurrence time of the first energy signal to obtain a start time when the first energy signal reaches 1.28 MeV;

[0105] Optionally, the stop detection module 730 includes:

[0106] A stop detector 7301, configured to detect a third energy signal generated by positron annihilation;

[0107] A second time extraction unit 7302, configured to extract the occurrence time of the third energy signal to obtain a stop time when the third energy signal reaches 0.511 MeV.

[0108] In the system according to an exemplary embodiment of the present disclosure, the start detector 7101 and the stop detector 7301 are scintillation detectors.

[0109] Among them, the start detector 7101 and the stop detector 7301 adopt scintillation detectors, which have the characteristic of high time resolution and can accurately measure the start time and the stop time. Also, in the present disclosure, the start time and the stop time are used for the statistics of the positron annihilation lifetime spectrum, while the coincidence time measured based on the luminescence characteristics of the liquid scintillation sample is only used for coincidence discrimination. Therefore, the accuracy of the measurement system is not affected by the performance of the liquid scintillation sample, ensuring the stability and high time resolution of the measurement system. In the embodiment of the present disclosure, the scintillation detector may be a plastic scintillation detector, a LYSO (lutetium yttrium silicate) detector, a LaBr3 detector, a BaF2 detector, etc., which are not specifically limited herein.

[0110] Optionally, the coincidence detection module 720 includes:

[0111] The coincidence detector 7201 is used to detect the second energy signal generated by the scintillation of positrons in the liquid scintillation sample;

[0112] The third time extraction unit 7202 is used to extract the occurrence time of the second energy signal to obtain the coincidence time when the second energy signal reaches the energy threshold corresponding to the electronic noise.

[0113] Among them, the first time extraction unit 7102, the second time extraction unit 7302, and the third time extraction unit 7202 can respectively extract the time information of the energy signals in the start detector 7101, the stop detector 7301, and the coincidence detector 7201, and simultaneously generate a logic signal and a timing signal. The time extraction unit can discriminate the energy signals detected by the detector and output a logic signal, a timing signal, etc. when the energy signal reaches the preset energy threshold. For the start detector 7101 and the stop detector 7301, the first time extraction unit 7102 and the second time extraction unit 7302 are respectively set with the energy thresholds of 1.28 MeV start gamma photons and 0.511 MeV annihilation gamma photons to ensure the measurement accuracy of the start time and the stop time and exclude the interference of other gamma backgrounds; for the coincidence detector 7201, the third time extraction unit 7202 can only be set with the energy threshold corresponding to the electronic noise. After excluding the energy signals generated by the electronic noise, all the energy signals generated by the scintillation in the liquid scintillation sample are collected to ensure the positron detection efficiency and avoid counting omission.

[0114] In the embodiment of the present disclosure, the coincidence detector 7201 is composed of a liquid scintillation sample coupled with a photomultiplier tube.

[0115] In the embodiments of the present disclosure, the start detector 7101 can input a first energy signal to the first time extraction unit 7102. When the first energy signal reaches 1.28 MeV, the first time extraction unit 7102 can input a logic signal to the coincidence selection unit 7401 and simultaneously input a timing signal to the time difference calculation unit 7402. The stop detector 7301 can input a third energy signal to the second time extraction unit 7302. When the third energy signal reaches 0.511 MeV, the second time extraction unit 7302 can input a timing signal to the time difference calculation unit 7402. The coincidence detector 7202 can input a second energy signal to the third time extraction unit 7202. When the second energy signal reaches the energy threshold of the electronic noise, the third time extraction unit 7202 can input a logic signal to the coincidence selection unit 7401. When the coincidence selection unit 7401 receives the logic signals from the first time extraction unit 7102 and the third time extraction unit 7202 within the first time window, it can input a trigger signal to the time difference calculation unit 7402. When the time difference calculation unit 7402 receives the trigger signal and receives the timing signals from the first time extraction unit 7102 and the second time extraction unit 7302 within the second time window, it can calculate the annihilation lifetime of the positron according to the two-way timing signals and input it to the lifetime spectrum statistics unit 7403. The lifetime spectrum statistics unit 7403 can count the annihilation lifetime of each positron in the liquid scintillator sample by setting the channel width and the number of channels, so as to obtain the positron annihilation lifetime spectrum of the liquid scintillator sample. Additionally, in actual measurement, the radiation source and the liquid scintillator sample need to be placed in a dark room to achieve complete light shielding and avoid the interference of ambient light on the signal.

[0116] In the practical application of the embodiments of the present disclosure, the first time extraction unit 7102, the second time extraction unit 7302, and the third time extraction unit 7202 may adopt a CFDD (Constant Fraction Differential Discriminator). At this time, based on the energy window selection function of the CFDD, different energy thresholds can be set in the form of a photopeak energy window, so as to extract the time of different energy signals within the photopeak energy window and obtain the occurrence time of the corresponding energy signal. The time difference calculation unit 7402 may adopt a TAC (Time-amplitude Converter); the lifetime spectrum statistics unit 7403 may adopt an MCA (Multi-channel Analyzer) and a PC (Personal Computer). Among them, the MCA is used to measure and statistically obtain the positron annihilation lifetime spectrum of the amplitude output by the TAC, and the PC is used to obtain and display the positron annihilation lifetime spectrum; the coincidence selection unit 7401 may adopt a Fast Coincidence (fast coincidence unit). The above description is only for illustration. Those skilled in the art can select different electronic devices to implement the present disclosure according to actual application requirements, measurement conditions, etc. Figure 6 , 7 the functions in the system shown, and the present disclosure does not make specific limitations here.

[0117] In the system according to an exemplary embodiment of the present disclosure, the first time window is less than 1 nanosecond.

[0118] In the system according to an exemplary embodiment of the present disclosure, the data statistics module 740 is specifically configured to statistically obtain the positron annihilation lifetime spectrum of the liquid scintillation sample according to the start time and the stop time when the start time and the coincidence time meet the preset coincidence selection conditions and the start time and the stop time are obtained within the second time window, and the second time window is set according to the annihilation lifetime of positrons in the liquid scintillation sample.

[0119] It should be noted that although several modules or units of devices for action execution are mentioned in the above detailed description, this division is not mandatory. In fact, according to the embodiments of the present disclosure, the features and functions of two or more modules or units described above may be embodied in one module or unit. Conversely, the features and functions of one module or unit described above may be further divided and embodied by multiple modules or units.

[0120] Moreover, although the steps of the methods in this disclosure are depicted in a specific order in the accompanying drawings, this does not require or imply that these steps must be carried out in that specific order, or that all of the steps shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step for execution, and / or one step may be broken down into multiple steps for execution, etc.

[0121] From the description of the above embodiments, those skilled in the art can easily understand that the exemplary embodiments described herein can be implemented by software, or by a combination of software and necessary hardware. Therefore, the technical solutions according to the embodiments of this disclosure can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (which can be a CD-ROM, USB flash drive, mobile hard disk, etc.) or on a network, including several instructions to enable a computing device (which can be a personal computer, server, mobile terminal, or network device, etc.) to execute the methods according to the embodiments of this disclosure.

[0122] In an exemplary embodiment of this disclosure, an electronic device capable of implementing the above method is also provided.

[0123] Those skilled in the relevant technical fields can understand that various aspects of this disclosure can be implemented as a system, method, or program product. Therefore, various aspects of this disclosure can be specifically implemented in the following forms, namely: a complete hardware implementation, a complete software implementation (including firmware, microcode, etc.), or an implementation combining hardware and software aspects, which can be collectively referred to herein as "circuitry", "module", or "system".

[0124] Reference is now made to Figure 8 describe the electronic device 800 according to this embodiment of this disclosure. Figure 8 The electronic device 800 shown is merely an example and should not impose any limitations on the functions and usage scope of the embodiments of this disclosure.

[0125] As Figure 8 shown, the electronic device 800 is presented in the form of a general-purpose computing device. The components of the electronic device 800 may include, but are not limited to: at least one of the above-mentioned processing units 810, at least one of the above-mentioned storage units 820, and a bus 830 connecting different system components (including the storage unit 820 and the processing unit 810).

[0126] Among them, the storage unit stores program code, and the program code can be executed by the processing unit 810, so that the processing unit 810 executes the steps according to various exemplary embodiments of this disclosure described in the "Exemplary Methods" section of this specification.

[0127] The storage unit 820 may include a readable medium in the form of a volatile storage unit, such as a random access storage unit (RAM) 8201 and / or a cache storage unit 8202, and may further include a read-only storage unit (ROM) 8203.

[0128] The storage unit 820 may also include a program / utilities 8204 having a set (at least one) of program modules 8205. Such program modules 8205 include, but are not limited to: an operating system, one or more application programs, other program modules, and program data. Each or some combination of these examples may include an implementation of a network environment.

[0129] The bus 830 may represent one or more of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, a processing unit, or a local bus using any of a variety of bus structures.

[0130] The electronic device 800 may also communicate with one or more external devices 800 (such as a keyboard, a pointing device, a Bluetooth device, etc.), may also communicate with one or more devices that enable a user to interact with the electronic device 800, and / or may communicate with any device that enables the electronic device 800 to communicate with one or more other computing devices (such as a router, a modem, etc.). Such communication may be carried out through the display unit 840 and an input / output (I / O) interface 850 connected to the display unit 840. Moreover, the electronic device 800 may also communicate with one or more networks (such as a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) through a network adapter 860. As shown in the figure, the network adapter 860 communicates with other modules of the electronic device 800 through the bus 830. It should be understood that although not shown in the figure, other hardware and / or software modules may be used in conjunction with the electronic device 800, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems, etc.

[0131] Through the description of the above embodiments, those skilled in the art can easily understand that the exemplary embodiments described herein can be implemented by software, or can be implemented by a combination of software and necessary hardware. Therefore, the technical solutions according to the embodiments of the present disclosure can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.) or on a network, including several instructions to enable a computing device (which can be a personal computer, a server, a terminal device, or a network device, etc.) to execute the method according to the embodiments of the present disclosure.

[0132] In an exemplary embodiment of the present disclosure, there is also provided a computer-readable storage medium, on which a program product capable of implementing the above methods in this specification is stored. In some possible implementation manners, various aspects of the present disclosure can also be implemented in the form of a program product, which includes program code. When the program product runs on a terminal device, the program code is used to cause the terminal device to execute the steps according to various exemplary embodiments of the present disclosure described in the above "Exemplary Method" section of this specification.

[0133] In an embodiment of the present disclosure, there is also provided a program product for implementing the above method. It can be a portable compact disc read-only memory (CD-ROM) and includes program code, and can run on a terminal device, such as a personal computer. However, the program product of the present disclosure is not limited to this. In this document, a readable storage medium can be any tangible medium that contains or stores a program, and this program can be used by or in combination with an instruction execution system, device, or component.

[0134] The program product can adopt any combination of one or more readable media. The readable media can be a readable signal medium or a readable storage medium. The readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or component, or any combination of the above. More specific examples (non-exhaustive list) of the readable storage medium include: an electrical connection with one or more wires, a portable disc, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0135] The computer-readable signal medium can include a data signal propagated in a baseband or as part of a carrier wave, on which the readable program code is carried. Such a propagated data signal can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. The readable signal medium can also be any readable medium other than the readable storage medium, and this readable medium can send, propagate, or transmit a program for use by or in combination with an instruction execution system, device, or component.

[0136] The program code contained on the readable medium can be transmitted by any suitable medium, including but not limited to wireless, wired, optical fiber, RF, etc., or any suitable combination of the above.

[0137] Program code for performing the operations of the present disclosure may be written in any combination of one or more programming languages, including object-oriented programming languages such as Java, C++, etc., and also including conventional procedural programming languages such as the "C" language or similar programming languages. The program code may execute entirely on the user's computing device, partly on the user's device, as a stand-alone software package, partly on the user's computing device and partly on a remote computing device, or entirely on a remote computing device or server. In the case of a remote computing device, the remote computing device may be connected to the user's computing device through any kind of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computing device (e.g., through the Internet using an Internet service provider).

[0138] In addition, the above drawings are only schematic illustrations of the processes included in the method according to the exemplary embodiments of the present disclosure, and are not for limiting purposes. It is easy to understand that the processes shown in the above drawings do not indicate or limit the chronological order of these processes. Additionally, it is also easy to understand that these processes may be executed, for example, synchronously or asynchronously in multiple modules.

[0139] Other embodiments of the present disclosure will be readily apparent to those skilled in the art after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include known common knowledge or conventional technical means in the technical field not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of the present disclosure are pointed out by the claims.

Claims

1. A method for measuring positron annihilation lifetime spectrum for liquid scintillation characterization, characterized in that The method includes: Detecting a first energy signal generated by the decay of a radiation source to obtain a start time, where the energy threshold of the first energy signal is set according to the energy of an initial gamma photon, and the initial gamma photon is generated by the decay of the radiation source; Detecting a second energy signal of a positron to obtain a coincidence time, where the positron is released by the radiation source and enters a liquid scintillation sample, the energy threshold of the second energy signal is set according to electronic noise, the liquid scintillation sample is arranged on one side of the radiation source and is separated from the radiation source by a preset distance; Detecting a third energy signal generated by the annihilation of the positron to obtain a stop time, where the energy threshold of the third energy signal is set according to the energy of an annihilation gamma photon, and the annihilation gamma photon is generated by the annihilation of the positron; When the start time and the coincidence time meet a preset coincidence selection condition, statistically analyzing a positron annihilation lifetime spectrum of the liquid scintillation sample according to the start time and the stop time; the preset coincidence selection condition includes that the start time and the coincidence time are obtained within a first time window; The step of statistically analyzing a positron annihilation lifetime spectrum of the liquid scintillation sample according to the start time and the stop time when the start time and the coincidence time meet a preset coincidence selection condition includes When the start time and the coincidence time meet a preset coincidence selection condition, and the start time and the stop time are obtained within a second time window, statistically analyzing a positron annihilation lifetime spectrum of the liquid scintillation sample according to the start time and the stop time, where the second time window is set according to the annihilation lifetime of the positron in the liquid scintillation sample.

2. The method according to claim 1, characterized in that, The first time window is less than 1 nanosecond.

3. A positron annihilation lifetime spectroscopy measurement system for liquid scintillation characterization, characterized in that, The system includes: A start detection module, configured to detect a first energy signal generated by the decay of a radiation source to obtain a start time, where the energy threshold of the first energy signal is set according to the energy of an initial gamma photon, and the initial gamma photon is generated by the decay of the radiation source; A coincidence detection module, configured to detect a second energy signal of a positron to obtain a coincidence time, where the positron is released by the radiation source and enters a liquid scintillation sample, the energy threshold of the second energy signal is set according to electronic noise, the liquid scintillation sample is arranged on one side of the radiation source and is separated from the radiation source by a preset distance; A stop detection module, configured to detect a third energy signal generated by the annihilation of the positron to obtain a stop time, where the energy threshold of the third energy signal is set according to the energy of an annihilation gamma photon, and the annihilation gamma photon is generated by the annihilation of the positron; A data statistics module, configured to statistically analyze a positron annihilation lifetime spectrum of the liquid scintillation sample according to the start time and the stop time when the start time and the coincidence time meet a preset coincidence selection condition; the preset coincidence selection condition includes that the start time and the coincidence time are obtained within a first time window; The data statistics module is specifically configured to, when the start time and the coincidence time meet the preset coincidence selection conditions, and the start time and the stop time are obtained within a second time window, statistically analyze the positron annihilation lifetime spectrum of the liquid scintillation sample according to the start time and the stop time, where the second time window is set according to the annihilation lifetime of positrons in the liquid scintillation sample.

4. The system according to claim 3, wherein The data statistics module includes: A coincidence selection unit, configured to output a trigger signal when the start time and the coincidence time meet the preset coincidence selection conditions; A time difference calculation unit, configured to calculate the positron annihilation lifetime according to the start time and the stop time when receiving the trigger signal; A lifetime spectrum statistics unit, configured to statistically analyze the positron annihilation lifetime spectrum of the liquid scintillation sample according to the positron annihilation lifetime.

5. The system according to claim 3, wherein The first time window is less than 1 nanosecond.

6. The system according to claim 3, wherein The start detection module includes: A start detector, configured to detect a first energy signal generated by the decay of the radiation source; A first time extraction unit, configured to extract the occurrence time of the first energy signal to obtain the start time when the first energy signal reaches 1.28 MeV; The stop detection module includes: A stop detector, configured to detect the third energy signal generated by positron annihilation; A second time extraction unit, configured to extract the occurrence time of the third energy signal to obtain the stop time when the third energy signal reaches 0.511 MeV.

7. The system according to claim 6, wherein The start detector and the stop detector are scintillation detectors.

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