CN106443758A - Anticoincidence based positron annihilation detecting method and system - Google Patents

Abstract

The present application discloses a method and system for detecting positron annihilation based on anti-coincidence. The method comprises: using a radioactive source to generate positrons, the positrons including first positrons entering the sample and second positrons entering the scintillator; acquiring gamma photon signals generated by the annihilation of the positrons, the gamma photon signals Including the first gamma photon signal generated by the first positron annihilation and the second gamma photon signal generated by the second positron annihilation; acquiring the scintillation sheet when the second positron passes through the scintillation sheet A first signal is generated; according to the first signal, the second gamma photon signal is removed from the gamma photon signal. This method is able to remove invalid gamma photon signals.

Description

Method and system for detecting positron annihilation based on anticoincidence

technical field

The invention relates to the technical field of nuclear spectroscopy and nuclear detection, in particular to a method and system for detecting positron annihilation based on anticoincidence.

Background technique

The positrons emitted by the radioactive source are injected into the sample to be tested, and after thermal diffusion, they annihilate with the electrons in the sample to be tested, and emit gamma photons. The generation time of the gamma photons and the momentum and energy information they carry are respectively Corresponding to the lifetime of the positron in the material, the momentum and energy distribution information of the annihilated electron can reflect the microstructure of the sample material to be tested.

In the conventional measurement method shown in Figure 1, two identical samples are used to tightly clamp the radioactive source for positron measurement. Fig. 1 is a schematic block diagram of a "sandwich" structure positron annihilation measurement system according to the prior art. As shown in Figure 1, a "sandwich" structure positron annihilation measurement system 100 includes: a radiation source 103, a start signal detector 105, a stop signal detector 107, a first constant ratio timer 109, a delayer 111, a first Two constant-ratio timers 113 , a time-to-amplitude converter 115 and a multi-channel analyzer 117 . The sample to be tested 101 is also shown in the figure.

The working principle of the "sandwich" structure positron annihilation measurement system is: usually the radioactive source is ²² Na, and the positrons emitted by the radioactive source are accompanied by the generation of 1.28MeV characteristic gamma photons. In the positron lifetime spectrum measurement, this feature is selected Gamma photons serve as the initiation signal for positron annihilation. After the positron is annihilated in the material, most of them emit two gamma photons with an energy range of about 0.511MeV, and the two photons are emitted at an angle of about 180 degrees. The gamma photon is selected as the termination signal and the start signal of the positron annihilation The time difference between the positron and the termination signal is the lifetime of the positron, and the positron lifetime spectrum is formed through the statistics of a large number of events. At the same time, using the same test system, the Doppler broadening spectrum can also be obtained by measuring the energy spectrum of 0.511MeV gamma photons, and the momentum angle correlation spectrum can be obtained by measuring the emission angle distribution of 0.511MeV gamma photon pairs.

In the "sandwich" structure positron annihilation measurement system, the positrons are generated by the radioactive source 103, which is sandwiched between two identical samples 101, and placed at the start signal detector 105 and the stop signal detector 107. between the detectors. The start signal detector 105 and the stop signal detector 107 are composed of BaF2 crystal (or plastic scintillator) and photomultiplier tube. The first constant ratio timer 109 and the second constant ratio timer 113 can select the energy of the detected photons, and can also generate a timing signal when a photon is detected. The second constant ratio timer 113 is connected to the delayer 111 , and the delayer 111 delays the signal received by the second constant ratio timer 113 . The time-amplitude converter 115 converts the time interval between the signal transmitted by the first constant ratio timer 109 and the signal transmitted by the delayer 111 into a pulse signal whose height is directly proportional to it, and this pulse signal is input into multi-channel analysis device 117, and then obtain the lifetime spectrum of the positron.

Due to the limited structure, the conventional method shown in Figure 1 cannot realize on-site material detection and liquid sample measurement, and the change of the sample environment is limited, so the application range is limited.

In view of this, the β+-γ coincident positron annihilation method was developed, as shown in Figure 2. β+-γ conforms to the positron annihilation method. The plastic scintillator is used to directly detect the generation moment of the positron, and the annihilation of the positron is measured by detecting the time difference between the moment when the positron passes through the scintillator and the moment when the annihilation pair emits gamma rays. life.

Fig. 2 is a schematic block diagram of a "β+-γ" consistent positron annihilation measurement system according to the prior art. As shown in Figure 2, a "β+-γ" coincident positron annihilation measurement system 200 includes: a radiation source 203, a scintillation sheet 205, a start signal detector 207, a stop signal detector 209, a first timer 211, a second A second timer 213 , a photomultiplier tube 215 , a third timer 217 , a time-to-amplitude converter 219 , a coincidence circuit 221 and a multi-channel analyzer 223 . The sample to be tested 201 is also shown in the figure.

The working principle of the β ⁺ -γ accord with the positron annihilation measurement system is: use the plastic scintillator to directly detect the generation moment of the positron, and measure the The annihilation lifetime of the positron is obtained. The β ⁺ -γ positron lifetime measurement uses the pulse signal generated by β ⁺ directly passing through the scintillator as the time start signal. In order to ensure that the positron has enough energy to penetrate the scintillator and annihilate on the sample, a high positron energy (1.89 MeV), ⁶⁸ Ge with a longer half-life (276d) was used as the radioactive source for measurement. A Pb shield with a thickness of about 2 cm is installed outside the probe to collimate and block the influence of annihilation gamma rays in the light guide on the stop probe and coincident probe.

In the β ⁺ -γ coincident positron annihilation measurement system, the positrons are generated by the radioactive source 203, and the radioactive source 203 is located between the scintillator 205 and the photomultiplier tube 215, and the radioactive source 203, the scintillator 205 and the photomultiplier tube 215 act as one As a whole, it is placed between the start signal detector 207 and the stop signal detector 209 . The first timer 211 and the second timer 213 can select the energy of the detected photons, and can also generate a timing signal when a photon is detected. The third timer 217 performs energy selection on the detected signal passing through the photomultiplier tube, and can also generate a timing signal when detecting the signal passing through the photomultiplier tube.

The first timer 211 and the second timer 213 transmit the processed signal to the coincidence circuit 221 for coincidence processing. The signal processed by the coincidence process and the signal processed by the third timer 217 are sent to the time-to-amplitude converter 219 . The time-to-amplitude converter 219 converts the time interval between the signal sent by the fast coincidence circuit 221 and the signal sent by the third timer 217 into a pulse signal whose height is directly proportional to it. The pulse signal is input into the multi-channel analyzer 223 to obtain the lifetime spectrum of the positron.

The positron annihilation measurement method shown in Figure 2 can realize the non-contact measurement of samples and radioactive sources. But, first, because the scintillator absorbs positrons, the thicker the scintillator, the more energy deposited by the positrons, the higher the signal strength, but the fewer the number of positrons that can pass through the scintillator, and the positrons penetrate aluminum foil and air There is also positron annihilation loss in the process. The farther the sample is from the radioactive source, the fewer the number of positrons annihilated on the sample, and the high energy of the positrons is required, which limits the selection of the source; secondly, the use of lead shielding collimator does not absorb The annihilated positrons in the sample, as well as the gamma rays produced by the annihilation, will reduce the number of effective positrons; finally, the effective gamma rays are gated through the coincidence of two barium fluoride detectors, and the detection efficiency and coincidence ratio are very large. The counting efficiency is limited to a certain extent. The above three factors cause the coincidence measurement method to sacrifice the counting efficiency of positrons, making the counting efficiency of the β+-γ coincidence positron annihilation measurement spectrometer low.

In view of the above problems, the present invention provides a method and system for detecting positron annihilation based on anti-coincidence.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in the art to a person of ordinary skill in the art.

Contents of the invention

In view of this, the present invention provides a method and system for detecting positron annihilation based on anti-coincidence to remove invalid gamma signals.

Other features and advantages of the invention will become apparent from the following detailed description, or in part, be learned by practice of the invention.

According to one aspect of the present invention, there is provided a method for detecting positron annihilation based on anticoincidence, which is characterized in that it includes: using a radioactive source to generate positrons, the positrons include the first positrons entering the sample and entering the scintillator the second positron; obtaining the gamma photon signal generated by the annihilation of the positron, the gamma photon signal including the first gamma photon signal generated by the annihilation of the first positron and the second gamma photon signal generated by the annihilation of the second positron; acquiring a first signal generated by the scintillator when the second positron passes through the scintillator; and removing the second gamma photon signal from the gamma photon signal according to the first signal.

In an exemplary embodiment of the present disclosure, the first signal is a fluorescent signal generated when the second positron passes through the scintillator.

In an exemplary embodiment of the present disclosure, the above method further includes: acquiring a characteristic gamma photon signal generated by the radiation source as an initial signal of positron annihilation.

In an exemplary embodiment of the present disclosure, removing the second gamma photon signal from the gamma photon signal includes: if the acquisition moment of the gamma photon signal and the acquisition moment of the fluorescence signal are within a preset time range , the gamma photon signal is excluded. .

According to another aspect of the present invention, there is provided a system for detecting positron annihilation based on anti-coincidence, comprising: a scintillator for generating fluorescence when a positron enters; an anti-coincidence detection system coupled with the scintillator, It is used to detect the first signal generated by the scintillator when the second positron entering the scintillator passes through the scintillator; the gamma photon detection system is used to obtain the gamma photon signal generated by the positron annihilation as the stop signal of the positron annihilation, And the characteristic gamma photon signal generated by the radiation source is used as the start signal of the positron annihilation; and a coincidence system is used to obtain the effective gamma photon signal according to the first signal, the start signal and the stop signal.

In an exemplary embodiment of the present disclosure, the anticoincidence detection system includes: a photomultiplier tube, configured to acquire the first signal generated when the positrons emitted by the radioactive source pass through the scintillator, and the scintillator is placed between the radioactive source and Between the photomultiplier tubes; the pre-amplifier is used to amplify the first signal; the main amplifier is used to further amplify the first signal amplified by the pre-amplifier; the single-channel analyzer is used to select the energy of the signal output by the main amplifier , and then converting the signal into a logic signal; and a first delayer, used for delaying the output signal of the single-channel analyzer.

In an exemplary embodiment of the present disclosure, a light guide is further included between the scintillation sheet and the photodiode.

In an exemplary embodiment of the present disclosure, the thickness of the scintillation sheet is between 0.2-10 mm, and it is composed of materials with an atomic number less than 20.

In an exemplary embodiment of the present disclosure, the gamma photon detection system includes: a start signal probe, which is used to acquire the characteristic gamma photon signal generated by the radioactive source as the start signal of positron annihilation; a stop signal probe, It is used to obtain the gamma photon signal generated by positron annihilation as the stop signal of positron annihilation; the first constant ratio timer is used to realize the judgment of the start signal of positron annihilation; the second constant ratio timer is used to realize Judging the positron annihilation stop signal; the second delayer is used to delay the signal output by the first constant ratio timer; and the third delayer is used to delay the signal output by the second constant ratio timer Delay.

In an exemplary embodiment of the present disclosure, the coincidence system includes: a coincidence unit, configured to receive the first signal, the start signal of the positron annihilation and the stop signal of the positron annihilation, and compare the first signal, the start signal and the The signal is judged. A time-to-amplitude converter, which is used to convert the time difference between the signal transmitted by the second delayer and the signal transmitted by the third delayer into a pulse signal whose height is proportional to the time difference; and multiple Trace analyzer for statistics on pulsed signals delivered by time-to-amplitude converters.

According to some embodiments of the present invention, the method and system for detecting positron annihilation based on anti-coincidence can realize the separation of the radioactive source and the sample, and can also shorten the distance between the sample and the radioactive source as much as possible.

The anti-coincidence-based method and system for detecting positron annihilation according to some embodiments of the present invention can at least partially exclude non-sample positron annihilation components.

It is to be understood that both the foregoing general description and the following detailed description are exemplary only and are not restrictive of the invention.

Description of drawings

The above and other objects, features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings.

Fig. 1 is a schematic block diagram of a "sandwich" structure positron annihilation measurement system according to the prior art.

Fig. 2 is a schematic block diagram of a "β+-γ" consistent positron annihilation measurement system according to the prior art.

Fig. 3 is a flowchart showing a method for detecting positron annihilation based on anti-coincidence according to an exemplary embodiment.

Fig. 4 is a flowchart showing another method for detecting positron annihilation based on anti-coincidence according to an exemplary embodiment. .

Fig. 5 is a block diagram of a system for detecting positron annihilation based on anti-coincidence according to an exemplary embodiment.

Explanation of reference signs:

"Sandwich" structure positron annihilation measurement system 100

radioactive source 103 start signal detector 105 stop signal detector 107

The first constant ratio timer 109 Delay device 111 The second constant ratio timer 113

Time-to-Amplitude Converter 115 Multichannel Analyzer 117 Test Sample 101

"β+-γ" corresponds to the positron annihilation measurement system 200

Radioactive source 203 Scintillation film 205 Start signal detector 207

Stop Signal Detector 209 First Timer 211 Second Timer 213

Photomultiplier tube 215 Third timer 217 Time-to-amplitude converter 219

Coincidence circuit 221 Multichannel analyzer 223 Sample to be tested 201

Anticoincidence-Based System for Detecting Positron Annihilation 500

Scintillation plate 502 Photomultiplier tube 504 Preamplifier 506

Main Amplifier 508 Single Channel Analyzer 510 Delay 512

Start signal probe 514 Stop signal probe 516 First constant ratio timer 518

The second constant ratio timer 520 The second delayer 522 The third delayer 524

Coincidence Unit 526 Time-to-Amplitude Converter 528 Multichannel Analyzer 530

Radioactive source 505 Sample to be tested 501

specific embodiment

Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many forms and should not be construed as limited to 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 example embodiments to those skilled in the art. The drawings are merely schematic illustrations of the invention 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.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided in order to give a thorough understanding of embodiments of the 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, devices, steps, etc. may be adopted. In other instances, well-known structures, methods, devices, implementations, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

Fig. 3 is a flowchart showing a method for detecting positron annihilation based on anti-coincidence according to an exemplary embodiment.

In step S302, a radiation source is used to generate positrons, and the positrons include first positrons entering the sample and second positrons entering the scintillator.

Matter is made up of atoms, and atoms are made up of nuclei and a certain number of electrons. The nucleus is in the center and is positively charged. Electrons move in specific orbits around the nucleus and are negatively charged. The entire atom has equal positive and negative charges and is neutral. The nucleus of an atom is composed of a certain number of protons and neutrons. There are slightly more neutrons than protons. The two numbers have a certain ratio. If there are too many or too few protons, there are too few or too many neutrons. The nucleus is often unstable, it can change spontaneously, emitting radiation and energy at the same time. In this embodiment, the positrons are generated by a radioactive source, such as ²² Na.

The radioactive source emits positrons into space. In this embodiment, the trajectory of positrons has no directivity, and positrons are scattered into space. Part of the positrons emitted by the radioactive source enters the sample to be tested and reacts with the sample to be tested, and the other part enters the scintillator and reacts with the scintillator.

In step S304, a gamma photon signal generated by positron annihilation is acquired, and the gamma photon signal includes a first gamma photon signal generated by the first positron annihilation and a second gamma photon signal generated by the second positron annihilation.

The radioactive source produces high-energy positrons and simultaneously produces gamma photons. After the high-energy positrons emitted by the radioactive source are injected into the matter, they first decelerate through a series of inelastic collisions in a very short time, and lose most of their energy. This process is called injection and thermalization. The thermalized positrons will undergo random diffusion thermal motion in the sample, and finally annihilate with electrons inside the material. Among them, the process in which positrons and electrons meet and both disappear simultaneously to produce gamma rays is called positron annihilation process. The time elapsed from the time a positron is injected into the sample to be annihilated is generally called the positron lifetime. Since positron annihilation occurs randomly, the positron annihilation lifetime can only be obtained statistically from a large number of annihilation events.

After thermal diffusion, the positrons annihilate with the electrons in the sample to be measured, and emit a gamma photon signal. For example, the gamma photon signal in this embodiment includes the first gamma photon signal generated by the annihilation of the first positron and The second gamma photon signal from the annihilation of the second positron.

For example, the radioactive source ²² Na generates 1.28MeV gamma photons while producing high-energy positrons. After the positrons are annihilated in the sample to be tested, most of them emit two gamma photons with an energy range of about 0.511MeV. Launch in 180-degree angle direction.

In step S306, a first signal generated by the scintillator when the second positron passes through the scintillator is acquired.

When gamma photons are injected into the scintillator, the Compton effect occurs. The Compton effect refers to the interaction of photons of short-wave electromagnetic radiation (such as: X-rays, gamma rays) with matter, resulting in the emission of Of the scattered rays, rays with longer wavelengths than the incident rays are produced. In this embodiment, the Compton effect occurs when gamma photons pass through the scintillator, and the energy of the recoil electrons generated by the Compton effect is absorbed by the scintillator to generate the first signal (in this embodiment, the This signal is called an anti-coincidence signal), that is to say, the Compton effect causes the second positron to pass through the scintillator, and the scintillator generates the first signal, such as a fluorescent signal.

In step S308, according to the first signal, the second gamma photon signal is removed from the gamma photon signal.

As mentioned above, the ²² Na radiation source produces positrons and 1.28MeV gamma photons, and a part of the positrons are annihilated in the sample to be tested to generate the first gamma photon signal, while the positrons that are not annihilated in the sample to be tested enter the scintillator, Annihilation in the scintillation plate produces a second gamma photon signal. In this embodiment, when the positrons entering the sample to be tested and the positrons entering the scintillator are annihilated, a gamma photon signal of 0.511 MeV will be generated. The positrons entering the scintillator generate a first signal, such as a fluorescent signal, while generating a 0.511 MeV gamma photon signal. According to the received first signal, the 0.511 MeV gamma signal from the scintillation plate can be removed from the received 0.511 MeV gamma photon signal by time exclusion method.

As mentioned above, the radioactive source is ²² Na. After the positrons emitted by the radioactive source are annihilated in the sample to be tested, most of them emit two gamma photons with an energy range of about 0.511 MeV, and the two photons are emitted at an angle of about 180 degrees. , in some embodiments, a gamma photon around 0.511 MeV is selected as the termination signal for positron annihilation. The time difference between the start signal and the stop signal is the lifetime of the positron. Through the statistics of the lifetime of a large number of positrons in the sample to be tested, the positron lifetime spectrum is finally formed.

In the method for detecting positron annihilation based on anti-coincidence in the embodiment of the present invention, the gamma signal that is not annihilated in the sample to be measured is excluded through the signal generated in the scintillation plate, and the gamma signal that is annihilated in the sample is obtained.

It should be clearly understood that this disclosure describes how to make and use specific examples, but the principles of the invention are not limited to any details of these examples. Rather, these principles can be applied to many other embodiments based on the teachings of the present disclosure.

In another method for detecting positron annihilation based on anti-coincidence according to another exemplary embodiment, a characteristic gamma photon signal generated by a radiation source is obtained as an initial signal of positron annihilation.

The emission of positrons from radioactive sources is accompanied by characteristic gamma photons. For example, the radiation source 22Na emits positrons accompanied by 1.28MeV characteristic gamma photons. In the positron lifetime spectrum measurement in this embodiment, for example, the characteristic gamma photon at 1.28 MeV can be selected as the start signal of positron annihilation.

Fig. 4 is a flow chart showing another method for detecting positron annihilation based on anti-coincidence according to an exemplary embodiment. The steps in FIG. 4 are further descriptions of step S308 “removing the second gamma photon signal from the gamma photon signal according to the first signal” in FIG. 3 . If the acquisition moment of the gamma photon signal and the acquisition moment of the fluorescent signal are within a preset time range, the gamma photon signal is excluded.

In step S402, the generation time of the gamma photon signal and the generation time of the fluorescence signal are acquired.

As mentioned above, the ²² Na radiation source produces positrons and 1.28MeV gamma photons, and a part of the positrons are annihilated in the sample to be tested to generate the first gamma photon signal, while the positrons that are not annihilated in the sample to be tested enter the scintillator, Annihilation in the scintillation plate produces a second gamma photon signal. After the positrons are annihilated in the sample to be tested, most of them emit two gamma photons with an energy range of about 0.511 MeV, and the two photons are emitted at an angle of about 180 degrees. In some embodiments, the energy range can be selected to be about 0.511 MeV The gamma photon is used as the termination signal of the positron annihilation. In this embodiment, the time when the second gamma photon signal is generated and the moment when the gamma photon of about 0.511 MeV is generated are obtained.

In step S404, it is determined whether the time is within a preset time range.

If the generation time of the second gamma photon signal and the generation time of the gamma photon of about 0.511 MeV are within the preset time range, go to step S406; otherwise go to step S408.

In step S406, the gamma photon signal at this moment is not recorded.

If the time at which the second gamma photon signal is generated is within the preset time range with that of the gamma photon at about 0.511 MeV, the gamma photon signal at this moment will not be recorded. As mentioned above, according to the received first signal, the 0.511 MeV gamma signal from the scintillation plate can be removed from the received 0.511 MeV gamma photon signal by time exclusion method. In this embodiment, this function is realized by an anti-coincidence circuit. The anticoincidence circuit does not record the 0.511 MeV gamma photon signal received at the current moment while detecting the first signal, for example, the fluorescence signal. Thus, the positron signal annihilated in the scintillation sheet is excluded.

In this embodiment, for example, positrons that are not annihilated in the sample will generate light signals when they pass through the scintillator, and then annihilate to generate 0.511MeV gamma photons. This process occurs instantaneously. According to the time correlation, if the detector detects When the photon signal is 0.511MeV, the PMT of the anti-coincidence detection unit also has a signal output, and the gamma photon signal is not recorded, so that the gamma photon signal that is not annihilated in the sample is excluded.

In step S408, the gamma photon signal at this moment is recorded.

If the time when the second gamma photon signal is generated and the time when the gamma photon around 0.511 MeV is generated is not within the preset time range, record the gamma photon signal at this time.

In this embodiment, when the gamma photon signal of 0.511 MeV is received, the anticoincidence circuit does not detect the first signal, for example, the fluorescence signal, and the gamma photon signal of 0.511 MeV received at the current moment is recorded.

The following are system embodiments of the present invention, which can be used to implement the method embodiments of the present invention. In the description of the system below, the parts that are the same as those of the aforementioned methods will not be repeated here.

Fig. 5 is a block diagram of a system for detecting positron annihilation based on anti-coincidence according to an exemplary embodiment. This system can be used, for example, in anticoincidence-based methods for detecting positron annihilation as shown in Fig. 3 or 4, but the invention is not limited thereto.

As shown in FIG. 5, a system 500 for detecting positron annihilation based on anti-coincidence includes:

The scintillation sheet 502 is used for generating fluorescence when positrons enter. In this embodiment, for example, the thickness of the scintillation sheet is between 0.2-1 mm, and it is made of materials with an atomic number less than 20. A light guide is also included between the scintillator plate 502 and the photomultiplier tube 504 .

As shown, the anticoincidence detection system is coupled to the scintillator 502 for detecting the first signal generated by the scintillator 502 when the second positron entering the scintillator passes through the scintillator 502 . The anti-coincidence detection system includes: a photomultiplier tube 504, an amplifier, a single-channel analyzer 510 and a first delayer 512, wherein the amplifier includes: a pre-amplifier 506 and a main amplifier 508, but the present invention is not limited thereto.

As shown in the figure, the gamma photon detection system is used to obtain the gamma photon signal generated by the positron annihilation as the stop signal of the positron annihilation, and the characteristic gamma photon signal generated by the radioactive source as the start signal of the positron annihilation; The gamma photon detection system includes: a start signal probe 514, a stop signal probe 516, a first constant ratio timer 518, a second constant ratio timer 520, a second delayer 522 and a third delayer 524, but this The invention is not limited thereto.

As shown in the figure, a coincidence system is used for obtaining an effective gamma photon signal according to the first signal, the start signal and the stop signal. The coincidence system includes: a coincidence unit 526 , a time-to-amplitude converter 528 and a multi-channel analyzer 530 , but the invention is not limited thereto.

In the anticoincidence system, the photomultiplier tube 504 is used to acquire the first signal generated when the positrons emitted by the radiation source pass through the scintillation plate, and the scintillation plate 502 is placed between the radiation source 505 and the photomultiplier tube 504 . A preamplifier 506, configured to amplify the first signal. The main amplifier 508 is configured to further amplify the first signal amplified by the pre-amplifier 506 . The single-channel analyzer 510 is used to perform energy selection on the signal output by the main amplifier 506, and then convert the signal into a logic signal. The first delayer 512 is configured to delay the output signal of the single-channel analyzer.

In the gamma photon detection system, the start signal probe 514 is used to acquire the characteristic gamma photon signal generated by the radiation source 505 as the start signal of positron annihilation. The stop signal probe 516 is used to acquire the gamma photon signal generated by the positron annihilation as the stop signal of the positron annihilation. The first constant ratio timer 518 is used to realize the judgment of the positron annihilation start signal. The second constant ratio timer 520 is used to realize the judgment of the positron annihilation stop signal. The second delayer 522 is configured to delay the signal output by the first constant ratio timer. The third delayer 524 is configured to delay the signal output by the second constant ratio timer.

In the coincidence system, the coincidence unit 526 is configured to receive the first signal, the start signal of the positron annihilation and the stop signal of the positron annihilation, and judge the first signal, the start signal and the stop signal. The time amplitude converter 528 is used to convert the time difference between the signal transmitted by the second delayer 522 and the signal transmitted by the third delayer 524 into a pulse signal whose height is proportional to the time difference . The multi-channel analyzer 530 is configured to perform statistics on the pulse signal transmitted by the time-to-amplitude converter.

A sample to be tested 501 is also shown in FIG. 5 .

In the embodiment provided by the present invention, of the positrons emitted by the radiation source 505 , a part of the positrons (first positrons) enters the sample to be tested, and another part of the positrons (the second positrons) enters the scintillator 502 . Positrons entering the scintillation plate 502 cause the scintillation plate to generate a fluorescent signal.

The signal detected by the stop signal probe 514 is input to the time-to-amplitude converter 528 after being timed by the first constant ratio timer 518 , roughly selected for energy, and appropriately delayed by the second delayer 522 . The signal detected by the start signal probe 514 is input to the time-to-amplitude converter 528 after being timed by the second constant ratio timer 520 , roughly selected for energy, and appropriately delayed by the third delayer 524 . The single-channel analysis function of the first constant-ratio timer and the second constant-ratio timer performs energy selection to realize the start signal (for example: 1.28MeV gamma photon signal) and stop signal (for example: 0.511MeV gamma photon signal) horse photon signal) judgment.

The photomultiplier tube 504 obtains the fluorescent signal generated by the scintillator 502, the output signal of the photomultiplier tube 504 is amplified by the pre-amplifier 506 and the main amplifier 508, and after the single-channel analyzer 510 performs appropriate energy selection (for example: noise signal removal), and The main amplifier 508 output waveform is converted into a logic signal. Afterwards, the signal is input into the coincidence unit 526 to realize anti-coincidence judgment. The output signal of the coincidence unit 526 is gated through the time-amplitude converter 528, and the gated time-amplitude converter 528 converts the time difference between the start time signal and the stop time signal obtained by the start signal probe 514 and the stop signal probe 516 into a signal amplitude The value is input to the multi-channel analyzer 630 for statistics, and the anticoincidence positron annihilation lifetime is obtained.

The system for detecting positron annihilation based on anti-coincidence according to some embodiments of the present invention is not only applicable to measurements under conventional conditions, but also applicable to measurements that can only be performed on a single sample (for example: non-sampling on-site detection, radioactive samples that are not Contact measurement, liquid sample surface measurement), and changing the measurement environment of the sample (for example: changing the temperature of the sample, changing the atmosphere of the sample's environment, or applying pressure to the sample) and other applications.

As mentioned above, the anti-coincidence-based method and system for detecting positron annihilation according to the embodiments of the present invention has at least one of the following advantages.

According to some embodiments of the present invention, the method and system for detecting positron annihilation based on anti-coincidence can realize the separation of the radioactive source and the sample, and can also shorten the distance between the sample and the radioactive source as much as possible.

The anti-coincidence-based method and system for detecting positron annihilation according to some embodiments of the present invention can at least partially exclude non-sample positron annihilation components.

It should be noted that the block diagrams shown in the above drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software, or in one or more hardware modules or integrated circuits, or in different network and/or processor means and/or microcontroller means.

Exemplary embodiments of the present invention have been specifically shown and described above. It should be understood that the invention is not limited to the detailed structures, arrangements or methods of implementation described herein; on the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (10)

1. A method for detecting positron annihilation based on anticoincidence, characterized in that, comprising: generating positrons using a radioactive source, the positrons comprising a first positron entering the sample and a second positron entering the scintillator plate; acquiring a gamma photon signal generated by positron annihilation, the gamma photon signal comprising a first gamma photon signal generated by the first positron annihilation and a second gamma photon signal generated by the second positron annihilation; acquiring a first signal generated by the scintillator when the second positron passes through the scintillator; The second gamma photon signal is removed from the gamma photon signal based on the first signal. 2. The method according to claim 1, wherein the first signal is a fluorescent signal generated when the second positron passes through the scintillator. 3. The method according to claim 1, further comprising: acquiring the characteristic gamma photon signal generated by the radiation source as the initial signal of positron annihilation. 4. The method according to claim 1, wherein removing the second gamma photon signal from the gamma photon signal comprises: if the acquisition time of the gamma photon signal is different from that of the fluorescence signal If the acquisition time is within the preset time range, the gamma photon signal is excluded. 5. A system for detecting positron annihilation based on anticoincidence, characterized in that it comprises: Scintillation sheet for fluorescence upon entry of positrons; an anti-coincidence detection system, coupled to the scintillator, for detecting the first signal generated by the scintillator when the second positron entering the scintillator passes through the scintillator; The gamma photon detection system is used to obtain the gamma photon signal generated by the positron annihilation as the stop signal of the positron annihilation, and the characteristic gamma photon signal generated by the radioactive source as the start signal of the positron annihilation; and A coincidence system is used for obtaining effective gamma photon signals according to the first signal, the start signal and the stop signal. 6. The system of claim 5, wherein the anti-coincidence detection system comprises: a photomultiplier tube, configured to acquire the first signal generated when the positrons emitted by the radiation source pass through the scintillation plate, and the scintillation plate is placed between the radiation source and the photomultiplier tube; an amplifier, configured to amplify the first signal; a single-channel analyzer for energy-selecting the signal output by the amplifier, and then converting the signal into a logic signal; and The first delayer is used to delay the output signal of the single-channel analyzer. 7. The system of claim 6, further comprising a light guide between the scintillator plate and the photomultiplier tube. 8. The system according to claim 5, wherein the thickness of the scintillation sheet is between 0.2-10 mm, comprising materials with an atomic number less than 20. 9. The system of claim 5, wherein the gamma photon detection system comprises: An initial signal probe, configured to obtain the characteristic gamma photon signal generated by the radioactive source as the initial signal of the positron annihilation; a stop signal probe, configured to acquire the gamma photon signal generated by the positron annihilation as the stop signal of the positron annihilation; The first constant ratio timer is used to realize the judgment of the positron annihilation start signal; The second constant ratio timer is used to realize the judgment of the positron annihilation stop signal; The second delayer is used to delay the signal output by the first constant ratio timer; and The third delayer is used to delay the signal output by the second constant ratio timer. 10. The system of claim 5, wherein the compliance system comprises: A coincidence unit is configured to receive the first signal, the start signal of the positron annihilation, and the stop signal of the positron annihilation, and judge the first signal, the start signal, and the stop signal. A time-to-amplitude converter for converting the time difference between the signal transmitted by the second delayer and the signal transmitted by the third delayer into a pulse whose height is proportional to the time difference signal; and A multi-channel analyzer is used to perform statistics on the pulse signal transmitted by the time-to-amplitude converter.