Positron annihilation lifetime measurement system

Abstract

The embodiment of the invention discloses a positron annihilation life measurement system. The positron annihilation life measurement system comprises a gamma ray generator, a first gamma ray detector, a second gamma ray detector and a life measurement module, wherein the gamma ray generator is used for generating a first gamma ray and a second gamma ray cascaded with the first gamma ray through nuclear reaction; wherein the first gamma ray is emitted to a detected sample, and positron annihilation occurs in the detected sample to generate a third gamma ray; the first gamma ray detector is used for detecting a second gamma ray to generate an initial signal; the second gamma ray detector is used for detecting a third gamma ray generation termination signal; and the life measurement module is used for measuring the time difference between the initial signal and the termination signal to generate a positron annihilation life spectrum.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on the Chinese patent application with application number 202422558552.6 and application date October 22, 2024, and claims the priority of the above-mentioned Chinese patent application. The entire content of the above-mentioned Chinese patent application is hereby introduced into this application as a reference. Technical Field

[0003] The invention relates to the technical field of positron annihilation, and in particular to a positron annihilation lifetime measurement system. Background Art

[0004] The length of the time interval from the end of thermalization to annihilation of a positron in a sample is closely related to the microstructure of the sample. The thermalization time of a positron entering a sample only takes a few ps, which is negligible compared to the time from the end of thermalization to annihilation. The commonly used positron annihilation lifetime, that is, the time from the generation of a positron to the annihilation of a positron entering a sample, can be used to study the microscopic defects of a sample.

[0005] The related technology generates positrons through isotope decay and analyzes the sample by irradiating the sample surface with positrons. The disadvantage of this method is that the positron penetration depth is shallow and can only obtain defects on the sample surface. It has requirements on the shape and state of the sample and cannot analyze thick and irregular samples. Summary of the invention

[0006] In view of this, an embodiment of the present invention provides a positron annihilation lifetime measurement system.

[0007] The technical solution of the embodiment of the present invention is achieved as follows:

[0008] An embodiment of the present invention provides a positron annihilation lifetime measurement system, the positron annihilation lifetime measurement system comprising: a gamma ray generator, a first gamma ray detector, a second gamma ray detector and a lifetime measurement module; wherein:

[0009] A gamma ray generator, used to generate a first gamma ray and a second gamma ray cascaded therewith through a nuclear reaction; wherein the first gamma ray is emitted toward a sample to be detected, and positron annihilation occurs in the sample to be detected to generate a third gamma ray;

[0010] a first gamma ray detector, used for detecting a start signal generated by the second gamma ray;

[0011] a second gamma ray detector, configured to detect the third gamma ray to generate a termination signal;

[0012] The lifetime measurement module is used to measure the time difference between the start signal and the end signal to generate a positron annihilation lifetime spectrum.

[0013] In the above scheme, the positron annihilation lifetime measurement system further includes:

[0014] A plurality of collimators are respectively arranged at the front ends of the first gamma-ray detector and the second gamma-ray detector.

[0015] In the above scheme, the gamma ray generator includes: a proton accelerator and an aluminum target.

[0016] In the above scheme, the gamma ray generator includes: a proton accelerator and a fluorine target.

[0017] In the above solution, the first gamma-ray detector and the second gamma-ray detector are scintillator detectors.

[0018] In the above solution, the first gamma-ray detector and the second gamma-ray detector include: a scintillator and a photomultiplier tube coupled thereto.

[0019] In the above solution, the life measurement module includes:

[0020] a first constant ratio discriminator, electrically connected to an output end of the first gamma-ray detector;

[0021] The second constant ratio discriminator is electrically connected to the output end of the second gamma ray detector.

[0022] In the above solution, the life measurement module further includes:

[0023] A first delay module, electrically connected to the output end of the first constant fraction discriminator;

[0024] The second delay module is electrically connected to the output end of the second constant fraction discriminator.

[0025] In the above solution, the life measurement module further includes:

[0026] A coincidence circuit is electrically connected to an output end of the first constant fraction discriminator and an output end of the second constant fraction discriminator.

[0027] In the above solution, the life measurement module further includes:

[0028] The time-to-amplitude converter is electrically connected to the output end of the first delay module, the output end of the second delay module, and the output end of the coincidence circuit.

[0029] The positron annihilation lifetime measurement system provided by the embodiment of the present invention comprises: a gamma ray generator, a first gamma ray detector, a second gamma ray detector and a lifetime measurement module; wherein the gamma ray generator is used to generate a first gamma ray and a second gamma ray cascaded therewith through a nuclear reaction; wherein the first gamma ray is directed to a sample to be detected, and positron annihilation occurs in the sample to be detected to generate a third gamma ray; the first gamma ray detector is used to detect a start signal for generating the second gamma ray; the second gamma ray detector is used to detect a stop signal for generating the third gamma ray; and the lifetime measurement module is used to measure the time difference between the start signal and the stop signal to generate a positron annihilation lifetime spectrum. The gamma ray generator of the embodiment of the present invention can generate a first gamma ray with discrete energy and high energy through a nuclear reaction, and the first gamma ray has strong penetrability. When the sample to be detected is irradiated with the first gamma ray, the probability of generating positrons by an electron pair effect in the sample to be detected is higher, so the positron annihilation lifetime spectrum is easier to measure, and the defects of thick and irregular samples can be analyzed. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings herein are incorporated into and constitute a part of the specification. These drawings illustrate embodiments consistent with the present invention and, together with the specification, are used to explain the technical solutions of the present invention.

[0031] Figure 1 A schematic structural diagram of a positron annihilation lifetime measurement system provided by the present invention;

[0032] Figure 2 A schematic structural diagram of another positron annihilation lifetime measurement system provided by the present invention;

[0033] Figure 3 A schematic structural diagram of another positron annihilation lifetime measurement system provided by the present invention;

[0034] Figure 4 A schematic diagram of another positron annihilation lifetime measurement system provided by the present invention

[0035] Figure 5 A schematic structural diagram of a life measurement module provided by the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention are further elaborated in detail below in conjunction with the drawings and embodiments. The described embodiments should not be regarded as limiting the present invention. All other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0037] In the following description, reference is made to "some embodiments", which describe a subset of all possible embodiments, but it is understood that "some embodiments" may be the same subset or different subsets of all possible embodiments, and may be combined with each other without conflict. The terms "first / second" are merely used to distinguish similar objects and do not represent a specific ordering of the objects. It is understood that "first / second" may be interchanged with a specific order or sequence where permitted, so that the embodiments of the present invention described herein can be implemented in an order other than that illustrated or described herein.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein are only for the purpose of describing the present invention and are not intended to limit the present invention.

[0039] Positrons are leptons. As the antiparticle of electrons, they can combine with electrons to annihilate and produce gamma radiation photons of a certain energy. Positron annihilation spectroscopy is a discipline that uses positrons as probes to characterize the microstructure of materials by detecting the time, energy and other information of gamma photons produced by electron annihilation. In the field of materials science, positron annihilation spectroscopy (PAS) is often referred to as positron annihilation technology. Its unique technical advantage is that it can provide information on atomic-scale local defects and microscopic phase transitions in sample materials, and the measurement process is non-destructive to the sample.

[0040] The length of the time interval from the end of thermalization to annihilation of a positron in a sample is closely related to the microstructure of the sample. The thermalization time of a positron entering a sample only takes a few ps, which is negligible compared to the time from the end of thermalization to annihilation. The positron annihilation lifetime, that is, the time from the generation of a positron to the annihilation of entering a sample, is often used to study the microscopic defects of a sample.

[0041] Currently, the commonly used positron sources are mainly isotope sources and accelerators. The samples are analyzed by irradiating the sample surface with positrons. This method can perform better measurements on thin film samples. However, the range of positrons in the sample is very small, so this method can only analyze the surface of the sample with a thickness of ~mm. It cannot analyze thick and irregular samples, nor can it measure internal defects of the material.

[0042] Related technologies provide a method for detecting material defects based on the electron pair effect, which is to bombard a tungsten target with electrons generated by an electron accelerator, generate gamma rays by bremsstrahlung, irradiate the sample with collimated and hardened gamma rays, generate positrons by the electron pair effect in the sample, annihilate the positrons with electrons in the material, and emit 0.511 MeV gamma rays, and measure the energy spectrum of the 0.511 MeV gamma rays to obtain the defects of the material. The disadvantage of this method is that the energy of the gamma rays generated by bremsstrahlung is continuous, with a large number of low-energy parts, and the probability of the occurrence of the electron pair effect is relatively low.

[0043] A similar technology is to use 22Na decay to emit 1.27MeV gamma rays and positrons. The positrons annihilate with the electrons in the material to emit 0.511MeV gamma rays. The time difference between the 1.27MeV gamma rays and the 0.511MeV gamma rays is measured and the lifetime spectrum is obtained by statistics. The concentration and type of material defects can be obtained through analysis. The disadvantage of this method is that the positron penetration depth is shallow, and only defects on the sample surface can be obtained. It has requirements on the shape and state of the sample.

[0044] The sample is analyzed by irradiating the sample surface with positrons using isotope source decay. This method can perform better measurements on thin film samples, but the range of positrons in the sample is very small, and it is not possible to analyze thick and irregular samples. Therefore, positrons are generated inside the sample and the positron annihilation lifetime spectrum is obtained. This is the key to applying positron annihilation to the defect characterization analysis of thick and irregular samples.

[0045] In view of the shortcomings of the above-mentioned related technologies, the present invention provides a positron annihilation lifetime measurement system, which can analyze thick and irregular samples and measure internal defects of materials.

[0046] Figure 1 A schematic diagram of the structure of a positron annihilation lifetime measurement system provided by the present invention is shown in FIG. Figure 1 As shown, the positron annihilation lifetime measurement system includes: a gamma ray generator 11, a first gamma ray detector 12, a second gamma ray detector 13 and a lifetime measurement module 14; wherein,

[0047] A gamma ray generator 11 is used to generate a first gamma ray and a second gamma ray cascaded therewith through a nuclear reaction; wherein the first gamma ray is emitted toward a sample to be detected, and positron annihilation occurs in the sample to generate a third gamma ray;

[0048] a first gamma ray detector 12, used for detecting a start signal generated by the second gamma ray;

[0049] a second gamma ray detector 13, configured to detect the third gamma ray to generate a termination signal;

[0050] The lifetime measurement module 14 is used to measure the time difference between the start signal and the end signal to generate a positron annihilation lifetime spectrum.

[0051] The gamma ray generator 11 generates high energy gamma rays and low energy gamma rays in cascade with them through nuclear reactions, the first gamma rays may be high energy gamma rays, the second gamma rays may be low energy gamma rays, and the third gamma rays are annihilation gamma rays generated by positron annihilation inside the sample.

[0052] The sample is irradiated with high-energy gamma rays. Gamma rays have strong penetrability and can generate positrons through interaction inside the sample. Positrons are generated by interaction inside the sample, and positrons annihilate in the sample to produce annihilation gamma rays.

[0053] The time t1 when the first gamma-ray detector 12 detects the second gamma ray is used as the positron generation time, and the time t2 when the second gamma-ray detector 13 detects the third gamma ray is used as the positron annihilation time. The lifetime measurement module 14 obtains the positron annihilation lifetime spectrum by counting the time difference between t1 and t2.

[0054] Among them, the gamma ray generator 11 has a high yield of gamma rays generated by nuclear reactions, and can generate quasi-monoenergetic high-energy gamma rays, which is conducive to interacting with samples to generate positrons. Compared with the gamma energy generated by isotope decay, the gamma energy generated by nuclear reactions is high, and the depth of the detected material is large. Nuclear reactions can generate energy-discrete and high-energy gamma rays, and the probability of generating positrons by electron pair effect is higher, and the counting rate is high and accurate, so the lifetime spectrum is easier to measure.

[0055] For example, the gamma ray generator 11 generates a second gamma ray with an energy of 1.78 MeV and a first gamma ray with an energy of 2.8 MeV, and the first gamma ray detector 12 detects the gamma ray of 1.78 MeV as a starting signal. The first gamma ray of 2.8 MeV is emitted to the sample to be detected, and interacts inside the sample to generate positrons, which annihilate in the sample to generate a third gamma ray of 0.511 MeV. The second gamma ray detector 13 is used to detect the third gamma ray of 0.511 MeV as a termination signal, and the time difference between the two signals is measured to obtain the positron annihilation lifetime spectrum.

[0056] Among them, the type and size of internal defects of the sample being tested can be determined based on the lifetime spectrum.

[0057] The positron annihilation lifetime measurement system provided by the embodiment of the present invention comprises: a gamma ray generator, a first gamma ray detector, a second gamma ray detector and a lifetime measurement module; wherein the gamma ray generator is used to generate a first gamma ray and a second gamma ray cascaded therewith through a nuclear reaction; wherein the first gamma ray is directed to a sample to be detected, and positron annihilation occurs in the sample to be detected to generate a third gamma ray; the first gamma ray detector is used to detect a start signal for generating the second gamma ray; the second gamma ray detector is used to detect a stop signal for generating the third gamma ray; and the lifetime measurement module is used to measure the time difference between the start signal and the stop signal to generate a positron annihilation lifetime spectrum. The gamma ray generator of the embodiment of the present invention can generate a first gamma ray with discrete energy and high energy through a nuclear reaction, and the first gamma ray has strong penetrability. When the sample to be detected is irradiated with the first gamma ray, the probability of generating positrons by an electron pair effect in the sample to be detected is higher, so the positron annihilation lifetime spectrum is easier to measure, and the defects of thick and irregular samples can be analyzed.

[0058] In some embodiments, the positron annihilation lifetime measurement system further comprises:

[0059] A plurality of collimators are respectively arranged at the front ends of the first gamma-ray detector and the second gamma-ray detector.

[0060] The collimator can focus the gamma rays onto the gamma ray detector, so that the number of gamma rays received by the gamma ray detector increases, thereby improving the detection efficiency.

[0061] like Figure 2 As shown, the positron annihilation lifetime measurement system includes a collimator 15 and a collimator 16 . The collimator 15 is arranged at the front end of the first gamma-ray detector 12 , and the collimator 16 is arranged at the front end of the second gamma-ray detector 13 .

[0062] In addition, a collimator may be arranged between the gamma ray generator and the sample to be detected.

[0063] In some embodiments, the gamma ray generator includes: a proton accelerator and an aluminum target.

[0064] In some embodiments, the gamma ray generator includes: a proton accelerator and a fluorine target.

[0065] For example, the nuclear reaction that generates high-energy gamma rays can use the resonance of protons and aluminum targets. The proton beam with an energy of 1.5MeV and an intensity of 0.5uA generated by the accelerator is hit on a thin aluminum target, and a resonance reaction occurs to generate gamma rays with energies of 1.78MeV and 2.8MeV. The yield of gamma rays generated by this nuclear reaction is high, and quasi-monoenergetic high-energy gamma rays can be generated, which is conducive to interacting with the sample to generate positrons.

[0066] In some embodiments, the first gamma ray detector and the second gamma ray detector are scintillator detectors.

[0067] In some embodiments, the first gamma ray detector and the second gamma ray detector include: a scintillator and a photomultiplier tube coupled thereto.

[0068] To ensure the accuracy of positron annihilation lifetime measurement, both the first gamma-ray detector and the second gamma-ray detector use scintillator detectors with high time resolution, such as BaF2 scintillator with good time performance and a photomultiplier tube coupled thereto.

[0069] like Figure 3 As shown, in some embodiments, the positron annihilation lifetime measurement system further includes:

[0070] The hardened body 17 is disposed at the front end of the second gamma-ray detector and is used to isolate signals other than the third gamma-ray.

[0071] Gamma rays directed at the sample will react with it in many ways, so a large number of annihilation photons, Compton scattered photons, photoelectron bremsstrahlung photons, and transmitted photons from the target head reach the detector, but the detector cannot distinguish them, which will cause serious accumulation. In order to reduce the number of photons reaching the detector to a more appropriate level, and to have an appropriate ratio of annihilation photons to other photons, so that the 0.511MeV gamma rays can be measured as undisturbed as possible, it is necessary to harden the beam before it reaches the detector, and to shield the area around the detector.

[0072] The detector will not only receive annihilation photons, but also other types of photons, such as Compton scattered photons, bremsstrahlung photons generated by photoelectron excitation, etc. It is difficult to distinguish them when they arrive at the detector at the same time, which leads to serious signal accumulation problems. In order to improve this situation, it is necessary to reduce the total number of photons reaching the detector and increase the ratio between annihilation photons and other photons so that the 0.511MeV annihilation photons can be measured more accurately and the interference can be reduced. To this end, ray hardening shielding measures can be implemented at the front end of the second gamma-ray detector. For example, a hardener can be set, and the material of the hardener can be Al or Pb. Let the 0.511MeV signal penetrate the hardener, so that the signal below 0.511MeV can be isolated, which can not only effectively reduce the number of photons in the energy spectrum, thereby reducing the severity of the accumulation phenomenon, but also filter out low-energy photons in the energy spectrum as much as possible.

[0073] Figure 4: is a schematic diagram of the structure of another positron annihilation lifetime measurement system provided by an embodiment of the present invention, the positron annihilation lifetime measurement system comprising:

[0074] The proton beam with energy of 1.5MeV and intensity of 0.5uA generated by the accelerator is hit on the thin AI aluminum target, and a resonance reaction occurs to generate γ rays with energy of 1.78MeV and 2.8MeV. The 1.78MeV γ rays are emitted to the detector 1 through the γ-ray collimator 5. The 2.8MeV high-energy γ rays irradiate the sample through the γ-ray collimator 1 and the γ-ray collimator 2, and interact inside the sample to generate positrons, which will annihilate in the sample to produce 0.511MeV annihilation γ rays. The 0.511MeV annihilation γ rays are emitted to the detector 2 through the γ-ray collimator 3 and the γ-ray collimator 4.

[0075] Among them, the electronics system corresponds to Figure 1 In the lifetime measurement module, the electronics system enables detector 1 to detect 1.78MeV gamma rays as the starting timing signal, and enables detector 2 to detect 0.511MeV gamma rays as the ending timing signal. By measuring the time difference between the two signals, the positron lifetime spectrum can be obtained.

[0076] The detector and the sample can be moved by a moving device.

[0077] Among them, the resonance reaction between protons and aluminum targets not only produces gamma rays with energies of 1.78MeV and 2.8MeV, but also produces low-energy gamma rays. These gamma rays are collimated and directed toward the sample. The low-energy gamma rays will affect the measurement of the lifetime spectrum, so the low-energy gamma rays need to be hardened and shielded.

[0078] Gamma rays directed at the sample will react with it in many ways, so a large number of annihilation photons, Compton scattered photons, photoelectron bremsstrahlung photons, and transmitted photons from the target head reach the detector, but the detector cannot distinguish them, which will cause serious accumulation. In order to reduce the number of photons reaching the detector to a more appropriate level, and to have an appropriate ratio of annihilation photons to other photons, so that the 0.511MeV gamma rays can be measured as undisturbed as possible, it is necessary to harden and shield the beam before it reaches the detector, shield the area around the detector, and adjust geometric factors such as the detector solid angle and detector distance.

[0079] In some embodiments, the lifetime measurement module includes:

[0080] a first constant ratio discriminator, electrically connected to an output end of the first gamma-ray detector;

[0081] The second constant ratio discriminator is electrically connected to the output end of the second gamma ray detector.

[0082] like Figure 5 As shown, the lifetime measurement module 14 includes a first constant ratio discriminator 141 and a second constant ratio discriminator 142 . The first constant ratio discriminator 141 is connected behind the output end of the first gamma ray detector 12 , and the second constant ratio discriminator 142 is connected behind the output end of the second gamma ray detector 13 .

[0083] The constant ratio discriminator is used to discriminate the energy of the start signal and the stop signal. For the start signal and the stop signal, the energy thresholds of the first constant ratio discriminator and the second constant ratio discriminator are set to the photoelectric peak of 1.78MeV gamma rays and the photoelectric peak of 0.511MeV gamma rays, respectively. This can improve the time measurement accuracy and eliminate other gamma background interference. After the two signals are discriminated, a start timing signal and a stop timing signal are generated.

[0084] For example, the signal detected by the gamma-ray detector is selected by the constant ratio discriminator in different energy windows as the starting signal (gamma signal with energy around 1.78 MeV) and the ending signal (gamma signal with energy around 0.511 MeV).

[0085] In some embodiments, the life measurement module further includes:

[0086] A first delay module, electrically connected to the output end of the first constant fraction discriminator;

[0087] The second delay module is electrically connected to the output end of the second constant fraction discriminator.

[0088] like Figure 5 As shown, the lifetime measurement module 14 includes a first delay module 143 and a second delay module 144 . The first delay module 143 is connected to the output end of the first constant fraction discriminator 141 , and the second delay module 144 is connected to the output end of the second constant fraction discriminator 142 .

[0089] The delay module is used to delay the start signal and the end signal.

[0090] In some embodiments, the life measurement module further includes:

[0091] A coincidence circuit is electrically connected to an output end of the first constant fraction discriminator and an output end of the second constant fraction discriminator.

[0092] like Figure 5 As shown, the lifetime measurement module 14 includes a coincidence circuit 145. The coincidence circuit 145 is a circuit for selecting a correlation signal, using time as a selection condition.

[0093] In some embodiments, the life measurement module further includes:

[0094] The time-to-amplitude converter is electrically connected to the output end of the first delay module, the output end of the second delay module, and the output end of the coincidence circuit.

[0095] like Figure 5 As shown, the lifetime measurement module 14 includes a time-to-amplitude converter 146 , which measures the time difference between the start signal and the stop signal as the lifetime of positron annihilation.

[0096] When the start gamma signal and the end gamma signal are detected simultaneously within the time window (nanosecond level), the gating signal of the positron annihilation event will be output. When no gating signal is output, it means that the two timing signals cannot represent the start and end time of a positron, and the time difference calculation between the start timing signal and the stop timing signal will be suppressed. The lifetime measurement module counts the time difference corresponding to each valid positron annihilation event, and after sufficient event accumulation, the positron annihilation lifetime spectrum can be generated.

[0097] exist Figure 5 In the diagram, multichannel is an electronic plug-in that can output signals. The horizontal and vertical axes are time difference and number respectively.

[0098] The various embodiments / implementations provided by the present invention can be combined with each other without causing any contradiction. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0099] The features, structures or characteristics described above may be combined in one or more embodiments in any suitable manner, and if possible, the features discussed in each embodiment are interchangeable. In the above description, many specific details are provided to provide a full understanding of the embodiments of the present invention. However, those skilled in the art will appreciate that the technical solution of the present invention may be practiced without one or more of the specific details, or other methods, components, materials, etc. may be adopted. In other cases, known structures, materials or operations are not shown or described in detail to avoid blurring various aspects of the present invention.

[0100] In this specification, the terms "a", "an", "the", "said" and "at least one" are used to indicate the presence of one or more elements / components / etc.; the terms "comprising", "including" and "having" are used to express an open-ended inclusion and mean that additional elements / components / etc. may exist in addition to the listed elements / components / etc.; the terms "first", "second" and "third" etc. are used only as labels and are not intended to limit the quantity of their objects.

[0101] It should be understood that the present invention is not limited in its application to the detailed structure and arrangement of the components proposed in this specification. The present invention can have other embodiments and can be implemented and executed in a variety of ways. The aforementioned variations and modifications fall within the scope of the present invention. It should be understood that the present invention disclosed and defined in this specification extends to all alternative combinations of two or more individual features mentioned or evident in the text and / or the drawings. All these different combinations constitute multiple alternative aspects of the present invention. The embodiments described in this specification illustrate the best mode known for implementing the present invention and will enable those skilled in the art to utilize the present invention.

Claims

1. A positron annihilation lifetime measurement system, characterized in that: include: A gamma ray generator, a first gamma ray detector, a second gamma ray detector and a lifetime measurement module; wherein, A gamma ray generator, used to generate a first gamma ray and a second gamma ray cascaded therewith through a nuclear reaction; wherein the first gamma ray is emitted toward a sample to be detected, and positron annihilation occurs in the sample to be detected to generate a third gamma ray; a first gamma ray detector, used for detecting a start signal generated by the second gamma ray; a second gamma ray detector, configured to detect the third gamma ray to generate a termination signal; The lifetime measurement module is used to measure the time difference between the start signal and the end signal to generate a positron annihilation lifetime spectrum.

2. The positron annihilation lifetime measurement system according to claim 1, characterized in that: The positron annihilation lifetime measurement system further comprises: A plurality of collimators are respectively arranged at the front ends of the first gamma-ray detector and the second gamma-ray detector.

3. The positron annihilation lifetime measurement system according to claim 1, characterized in that: The gamma ray generator includes a proton accelerator and an aluminum target.

4. The positron annihilation lifetime measurement system according to claim 1, characterized in that: The gamma ray generator includes a proton accelerator and a fluorine target.

5. The positron annihilation lifetime measurement system according to claim 1, characterized in that: The first gamma-ray detector and the second gamma-ray detector are scintillator detectors.

6. The positron annihilation lifetime measurement system according to claim 5, characterized in that: The first gamma-ray detector and the second gamma-ray detector include: a scintillator and a photomultiplier tube coupled thereto.

7. The positron annihilation lifetime measurement system according to claim 1, characterized in that: The life measurement module comprises: a first constant ratio discriminator, electrically connected to an output end of the first gamma-ray detector; The second constant ratio discriminator is electrically connected to the output end of the second gamma ray detector.

8. The positron annihilation lifetime measurement system according to claim 7, characterized in that: The life measurement module also includes: A first delay module, electrically connected to the output end of the first constant fraction discriminator; The second delay module is electrically connected to the output end of the second constant fraction discriminator.

9. The positron annihilation lifetime measurement system according to claim 8, characterized in that: The life measurement module also includes: a coincidence circuit electrically connected to an output terminal of the first constant fraction discriminator and an output terminal of the second constant fraction discriminator; The time-to-amplitude converter is electrically connected to the output end of the first delay module, the output end of the second delay module, and the output end of the coincidence circuit.

10. The positron annihilation lifetime measurement system according to claim 1, characterized in that: The positron annihilation lifetime measurement system further comprises: The hardened body is arranged at the front end of the second gamma-ray detector and is used for isolating signals other than the third gamma-ray.

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