A method for locating the annihilation point of orthopositronium

Abstract

The present invention relates to a method for locating the annihilation point of orthopositronium, belonging to the technical field of nuclear spectroscopy, and solves the problem of low measurement accuracy of the position of the o-Ps annihilation point. A method for locating the annihilation point of orthopositronium includes: orthopositronium undergoes 3γ annihilation, and a position-sensitive detector detects the incident time and incident position of three annihilation photons; a plane on which the incident positions of the three annihilation photons are coplanar is constructed as a positioning plane; on the positioning plane, based on the propagation relationship between the incident time, incident position of the three annihilation photons and the annihilation point, the annihilation point is located. This method proposes a new method and principle for locating the 3γ annihilation of orthopositronium, and can achieve rapid and accurate positioning of the annihilation point.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear spectroscopy, and particularly to a method for locating the annihilation point of ortho-positronium. Background Art

[0002] Positronium (abbreviated as Ps) is a metastable structure formed by the binding of a positron and an electron (similar to the structure of a hydrogen atom). Among them, the triplet positronium (o-Ps, ortho-positronium) with parallel spin directions has a lifetime of up to 142 ns and has a high probability of 3γ annihilation. The characteristics that o-Ps is uncharged and extremely sensitive to the surrounding microenvironment make it a non-destructive and highly sensitive probe, playing a unique role in basic physics, anti-matter science, characterization of the microscopic structure of materials, medical imaging, etc. For example, the angular correlation of positronium annihilation can be used for high-precision CPT measurement, the generation and storage of positronium can be used to obtain a high-brightness positron source, the positronium time-of-flight spectrum (Ps-TOF) can be used for characterizing the microporous structure near the surface of materials, and Ps event localization can be used to correct the imaging artifacts of positron emission tomography (PET). Among them, the core problem is how to accurately obtain the annihilation point distribution of Ps.

[0003] Traditional technical methods, such as detecting collimated annihilation gamma rays, reduce the detection solid angle at the cost of greatly reducing the counting efficiency and have limited accuracy; alternatively, by energy spectrum coincidence discrimination of 3γ annihilation events, it has extremely high requirements for the energy resolution of the detector and cannot completely avoid the false events caused by 2γ scattering; moreover, since Ps is an uncharged particle, it is impossible to detect the track of Ps through electromagnetic interaction similar to electrons or ions. Summary of the Invention

[0004] In view of the above analysis, the embodiments of the present invention aim to provide a method for locating the annihilation point of ortho-positronium to solve the problem of low measurement accuracy of the annihilation point position of o-Ps.

[0005] The present invention provides a method for locating the annihilation point of ortho-positronium, including:

[0006] When ortho-positronium undergoes 3γ annihilation, a position-sensitive detector detects the incident time and incident position of 3 annihilation photons;

[0007] Construct a positioning plane with the plane where the incident positions of the 3 annihilation photons are coplanar;

[0008] On the positioning plane, based on the propagation relationship between the incident time, incident position of the 3 annihilation photons and the annihilation point, locate the annihilation point.

[0009] On the basis of the above solution, the present invention has further made the following improvements:

[0010] Further, the annihilation point is located by the following method:

[0011] The maximum value, the second largest value, and the minimum value of the incident times T1, T2, and T3 of the three annihilation photons γ1, γ2, and γ3 are sequentially marked as T max , T mid , T min , and the incident positions corresponding to the maximum value, the second largest value, and the minimum value of the incident times T1, T2, and T3 are sequentially marked as

[0012] According to formula (1), the maximum radius R max and the second largest radius R mid are obtained:

[0013]

[0014] where c represents the propagation speed of light;

[0015] Taking Rmax as the radius and as the center, a circle O max is made. Taking R mid as the radius and as the center, a circle O mid is made. The center of the circle that is simultaneously externally tangent to circle O max and circle O mid is used as the annihilation point;

[0016] The three-dimensional coordinates of the annihilation point are obtained to realize the positioning of the annihilation point.

[0017] Further, the 3γ annihilation of the ortho-positronium includes: when the positronium emits a positronium particle beam, each ortho-positronium particle in the positronium particle beam flies in a vacuum pipeline and then undergoes 3γ annihilation; the vacuum pipeline is wrapped by the position-sensitive detector;

[0018] The method further includes:

[0019] According to the emission order of the ortho-positronium particles, the distribution N(z) along the z-axis direction in the three-dimensional coordinates (x, y, z) of the annihilation point corresponding to each ortho-positronium particle is sequentially counted to obtain the positronium time-of-flight spectrum.

[0020] Further, the method further includes:

[0021] According to the emission order of the ortho-positronium particles, the two-dimensional distribution N(x, y) of the annihilation point corresponding to each ortho-positronium particle in the transverse direction is sequentially counted for the cross-sectional diagnosis of the Ps beam.

[0022] Further, the method further includes:

[0023] According to the emission order of normal positronium particles, the three-dimensional spatial distribution N(x, y, z) of the annihilation points corresponding to each normal positronium particle is sequentially counted for the three-dimensional morphology diagnosis of the Ps beam.

[0024] Further, when the normal positronium undergoes 3γ annihilation, it further includes: in biological tissue, a β+ radioactive isotope drug emits positrons, and the positrons combine with electrons in the organism to form normal positronium and undergo 3γ annihilation;

[0025] At this time, the method further includes:

[0026] Count the three-dimensional spatial distribution N(x, y, z) of the annihilation points corresponding to the normal positronium to form a positron emission tomography image.

[0027] Further, the position-sensitive detector adopts a flat plate wrapping structure composed of 3 position-sensitive detection units, forming a detection area covering the transverse 2π detection solid angle perpendicular to the positronium beam and the radial annihilation position parallel to the positronium beam.

[0028] Further, the position-sensitive detector adopts an annular columnar structure, forming a 2π detection solid angle covering the x and y axis directions and a detection area along the z axis direction.

[0029] Further, when the normal positronium undergoes 3γ annihilation, it further includes:

[0030] The normal positronium undergoes 3γ annihilation in the sample, and the 3γ photons penetrate the sample and are detected by the position-sensitive detector; the normal positronium is wrapped inside the position-sensitive detector;

[0031] At this time, the method further includes:

[0032] Calculate the average time from the generation to the annihilation of each normal positronium respectively

[0033]

[0034] Wherein, respectively represent the distances between the annihilation point A and the incident positions S1, S2, S3 of the 3 annihilation photons γ1, γ2, γ3; wherein, T1, T2, T3 respectively represent the incident times of the 3 annihilation photons γ1, γ2, γ3; c represents the propagation speed of light;

[0035] Count the average time distribution from the generation to the annihilation of each normal positronium Obtain the positronium annihilation lifetime spectrum.

[0036] Furthermore, the position-sensitive detector adopts a hexahedron structure to form a detection area with a 4π detection solid angle.

[0037] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0038] The present invention provides a method for locating the annihilation point of ortho-positronium. Aiming at the problem of low measurement accuracy of the o-Ps annihilation point position, a new method and principle for locating the positronium annihilation point are proposed, which can realize the rapid and accurate positioning of the annihilation point and can solve the problem of high-precision measurement of the o-Ps annihilation point position.

[0039] In addition, this method can not only obtain the spatial distribution information of the positronium annihilation point, but also obtain the positronium annihilation state, including relevant information such as the energy distribution and momentum direction of 3γ, and can be used to construct devices such as a new type of high-resolution positronium time-of-flight spectrometer (Ps-TOF), a positronium beam diagnostic system, and a positron emission tomography device (PET).

[0040] In the present invention, the above technical solutions can also be combined with each other to realize more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification, or can be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained from the content specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals represent the same components.

[0042] Figure 1 It is a flow chart of the method for locating the annihilation point of ortho-positronium provided by the embodiment of the present invention;

[0043] Figure 2 It is a schematic diagram of the annihilation angle positioning principle provided by the embodiment of the present invention as Figure 2 ;

[0044] Figure 3 It is a schematic diagram of ortho-positronium in detection mode one using a position-sensitive detector with a flat plate wrapping structure;

[0045] Figure 4 It is a schematic diagram of ortho-positronium in detection mode two using a position-sensitive detector with an annular columnar structure;

[0046] Figure 5 It is a schematic diagram of ortho-positronium in detection mode three using a position-sensitive detector with a hexahedron structure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. The accompanying drawings form a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0048] A specific embodiment of the present invention discloses a method for locating the annihilation point of orthopositronium. The flowchart is as Figure 1 shown and includes the following steps:

[0049] Step S1: The orthopositronium undergoes 3γ annihilation, and the position-sensitive detector detects the incident time and incident position of the 3 annihilation photons.

[0050] Specifically, the orthopositronium (o-Ps) within the detection region undergoes 3γ annihilation, and the 3 annihilation photons γ1, γ2, and γ3 directly enter the position-sensitive detector. The position-sensitive detector obtains the incident position S and incident time T of the gamma rays: γ1(S1, T1), γ2(S2, T2), γ3(S3, T3).

[0051] Step S2: Construct a positioning plane with the plane where the incident positions of the 3 annihilation photons are coplanar.

[0052] Specifically, according to the law of conservation of momentum, the 3γ emission direction vectors are coplanar. A plane P and a triangle ΔS1S2S3 are constructed through the coplanarity of the three points S1, S2, and S3; the triangle ΔS1S2S3 lies on the plane P.

[0053] Step S3: On the positioning plane, based on the propagation relationship between the incident time, incident position of the 3 annihilation photons and the annihilation point, locate the annihilation point.

[0054] In step S3, the annihilation point is located by performing the following operations:

[0055] First, analyze the propagation relationship between the incident time, incident position of the 3 annihilation photons and the annihilation point: The difference between the three time signals T1, T2, and T3 reflects the propagation path difference of the gamma rays. The propagation path is the distance between the annihilation point A(x, y, z) and S1, S2, and S3 respectively. Principle of the positioning algorithm: Circles are drawn in the plane P with S1, S2, and S3 as the centers and as the radii respectively. The common intersection point of the three circles is the annihilation point A. Further analysis shows that, taking the three-dimensional coordinates of the annihilation point A as unknowns, the distances between the annihilation point A and the incident positions S1, S2, and S3 of the 3 annihilation photons γ1, γ2, and γ3 are written. Among them, The incident times T1, T2, and T3 of three annihilation photons γ1, γ2, and γ3 satisfy formula (1):

[0056]

[0057] where c is the speed of light propagation;

[0058] Therefore, the annihilation point A can be located through an algorithm based on the differences among T1, T2, and T3.

[0059] In the specific implementation process, based on the above principle analysis, the annihilation point positioning method in this embodiment is formed. The schematic diagram of the annihilation angle positioning principle is as Figure 2 shown and described as follows:

[0060] The maximum value, the second largest value, and the minimum value among the incident times T1, T2, and T3 of the three annihilation photons γ1, γ2, and γ3 are successively marked as T max 、T mid 、T min , and the incident positions corresponding to the maximum value, the second largest value, and the minimum value among the incident times T1, T2, and T3 are successively marked as

[0061] According to formula (2), the maximum radius Rmax and the second largest radius Rmid are obtained:

[0062]

[0063] where c represents the speed of light propagation;

[0064] Taking R max as the radius and as the center to make a circle O max , taking R mid as the radius and as the center to make a circle O mid , the center of the circle that is simultaneously externally tangent to circle O max 、circle O mid is taken as the annihilation point; the three-dimensional coordinates of the annihilation point are obtained to achieve the positioning of the annihilation point. The center track curve function of the circle that is simultaneously externally tangent to circle O max 、circle O mid is O(x, y, z) = 0. At this time, the function equation system has one and only one solution in the triangle ΔS1S2S3 region, which is A(x, y, z).

[0065] Exemplarily, assuming T1 < T2 < T3, circles O mid and O max are made with R mid and the corresponding S2 and S3 as the radius and the center respectivelymax , a circle that is externally tangent to two circles simultaneously can be obtained, and the function of its center trace curve O(x, y, z) = 0 is obtained. At this time, the function equation system can be expressed as: The function equation system has one and only one unique solution in the triangle ΔS1 S2 S3 region, which is A(x, y, z).

[0066] In this embodiment, for different purposes, the methods or devices for collecting the 3γ annihilation signals generated by positronium are also different. However, the execution processes of the corresponding steps S2 and S3 are the same. The specific description is as follows:

[0067] Method 1: For Ps-TOF measurement and Ps beam diagnosis

[0068] Step S1: When emitting a positronium particle beam, each normal positronium particle in the positronium particle beam flies in a vacuum pipeline and then undergoes 3γ annihilation; the vacuum pipeline is wrapped by the position-sensitive detector; taking the emission time t0 of Ps as the starting time, trigger the detector to collect data;

[0069] The execution processes of steps S2 - S3 remain unchanged;

[0070] After locating the annihilation point, in Method 1, the following information can also be obtained:

[0071] Step S4: According to the emission order of normal positronium particles, successively count the distribution N(z) along the z-axis direction in the three-dimensional coordinates (x, y, z) of the annihilation point corresponding to each normal positronium particle, and obtain the positronium time-of-flight (Ps-TOF) spectrum.

[0072] Step S5: According to the emission order of normal positronium particles, successively count the two-dimensional distribution N(x, y) in the transverse direction of the annihilation point corresponding to each normal positronium particle, for the cross-sectional flow diagnosis of the Ps beam;

[0073] Step S6: According to the emission order of normal positronium particles, successively count the three-dimensional spatial distribution N(x, y, z) of the annihilation point corresponding to each normal positronium particle, for the three-dimensional morphology diagnosis of the Ps beam.

[0074] Method 2: For positron emission tomography (PET) imaging

[0075] Step S1: In biological tissue, the β+ radioactive isotope drug emits positrons, and there is a certain probability that the positrons combine with electrons to form normal positronium (o-Ps). When the two combine, the positrons combine with the electrons in the organism to form normal positronium and undergo 3γ annihilation; the 3γ annihilation photons penetrate the biological tissue and are detected by the detection array;

[0076] The execution processes of steps S2 - S3 remain unchanged;

[0077] Step S4: Statistically analyze the three - dimensional spatial distribution N(x, y, z) of the annihilation points corresponding to the ortho - positronium to form a PET image.

[0078] In Method 1 and Method 2, the following two types of position - sensitive detectors can be selected:

[0079] Firstly, the position - sensitive detector adopts a flat - wrapped structure composed of 3 position - sensitive detection units, which is a continuous - crystal - type position - sensitive detection unit flat - wrapped structure, forming a detection area that covers a 2π detection solid angle in the transverse direction (x, y - axis directions) perpendicular to the positronium beam and the annihilation position in the radial direction (z - axis direction) parallel to the positronium beam. Exemplarily, at this time, the position - sensitive detection unit can be a continuous - crystal - type, array - type or strip - type position - sensitive detection unit. The schematic diagram of using the position - sensitive detector with a flat - wrapped structure to detect the ortho - positronium in Method 1 is as Figure 3 shown.

[0080] Secondly, the position - sensitive detector adopts an annular columnar structure composed of strip - crystal or array - crystal - type position - sensitive detection units, forming a detection area that covers a 2π detection solid angle in the x and y - axis directions and a detection area along the z - axis direction. Exemplarily, at this time, the position - sensitive detection unit can be a strip - crystal or array - crystal - type position - sensitive detection unit. The schematic diagram of using the position - sensitive detector with an annular columnar structure to detect the ortho - positronium in Method 2 is as Figure 4 shown.

[0081] Method 3: For positron annihilation spectroscopy

[0082] Step S1: The ortho - positronium undergoes 3γ annihilation in the sample, and the 3γ photons penetrate the sample and are detected by the position - sensitive detector; the ortho - positronium is enclosed within the position - sensitive detector;

[0083] The execution processes of steps S2 - S3 remain unchanged;

[0084] Step S4: Calculate the average time from the generation to the annihilation of each ortho - positronium

[0085] where, respectively represent the distances between the annihilation point A and the incident positions S1, S2, S3 of the three annihilation photons γ1, γ2, γ3; where, T1, T2, T3 respectively represent the incident times of the three annihilation photons γ1, γ2, γ3; c represents the speed of light;

[0086] Step S5: Statistically analyze the average - time distribution from the generation to the annihilation of each ortho - positronium to obtain the positronium annihilation lifetime spectrum.

[0087] In Method 3, the following position-sensitive detectors can be selected: The position-sensitive detector adopts a hexahedron structure composed of 6 position-sensitive detection units to form a detection area with a 4π detection solid angle. Exemplarily, at this time, the position-sensitive detection unit can be a continuous crystal type or an array crystal type position-sensitive detection unit. A schematic diagram of using the position-sensitive detector with a hexahedron structure to detect ortho-positronium in Method 3 is as Figure 5 shown.

[0088] In summary, the ortho-positronium annihilation point positioning method provided by the embodiments of the present invention proposes a new type of positronium annihilation point positioning method and principle for the problem of high-precision measurement of the o-Ps annihilation point position, which can achieve fast and accurate positioning of the annihilation point, and effectively solves the problem that the existing methods cannot achieve high-precision measurement of the o-Ps annihilation point position.

[0089] In addition, this method can not only obtain the spatial distribution information of the positronium annihilation point, but also obtain the positronium annihilation state, including relevant information such as the energy distribution and momentum direction of 3γ, and can be used to construct new high-resolution positronium time-of-flight spectrometers (Ps-TOF), positronium beam diagnostic systems, positron emission tomography equipment (PET) and other devices.

[0090] Those skilled in the art can understand that all or part of the processes of implementing the methods in the above embodiments can be completed by instructing relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium. Among them, the computer-readable storage medium is a magnetic disk, an optical disk, a read-only memory or a random access memory, etc.

[0091] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for locating the annihilation point of orthopositronium, characterized in that, Comprising: Orthopositronium undergoes 3γ annihilation, and a position-sensitive detector detects the incident times and incident positions of the 3 annihilation photons; Construct a plane where the incident positions of the 3 annihilation photons are coplanar as the positioning plane; On the said positioning plane, based on the propagation relationship between the incident times, incident positions of the 3 annihilation photons and the annihilation point, locate the annihilation point; Locate the annihilation point by the following method: Mark the maximum value, the second-largest value, and the minimum value of the incident times T1, T2, and T3 of the three annihilation photons γ1, γ2, and γ3 as T max , T mid , T min respectively, and mark the incident positions corresponding to the maximum value, the second-largest value, and the minimum value of the incident times T1, T2, and T3 as Obtain the maximum radius R according to formula (1) max and the second largest radius R mid : Wherein, c represents the propagation speed of light; With R max as the radius and as the center, draw a circle O max . With R mid as the radius and as the center, draw a circle O mid . Take the center of the circle that is externally tangent to both circle O max and circle O mid as the annihilation point; Obtain the three-dimensional coordinates of the annihilation point to achieve the positioning of the annihilation point.

2. The method for locating the annihilation point of orthopositronium according to claim 1, characterized in that, The orthopositronium undergoes 3γ annihilation, including: emitting a beam of orthopositronium particles, and each orthopositronium particle in the beam of orthopositronium particles flies in a vacuum pipeline and then undergoes 3γ annihilation; the vacuum pipeline is wrapped by the position-sensitive detector; The method further includes: According to the emission order of the orthopositronium particles, sequentially count the distribution N(z) along the z-axis direction in the three-dimensional coordinates (x, y, z) of the annihilation point corresponding to each orthopositronium particle, and obtain the orthopositronium flight time spectrum.

3. The method for locating the annihilation point of orthopositronium according to claim 2, wherein The method further includes: According to the emission order of the orthopositronium particles, sequentially count the two-dimensional distribution N(x, y) of the annihilation point corresponding to each orthopositronium particle in the transverse direction for the cross-sectional diagnosis of the Ps beam.

4. The method for locating the annihilation point of the normal positronium according to claim 2, characterized in that The method further includes: According to the emission order of the orthopositronium particles, sequentially count the three-dimensional spatial distribution N(x, y, z) of the annihilation point corresponding to each orthopositronium particle for the three-dimensional morphology diagnosis of the Ps beam.

5. The method for locating the annihilation point of orthopositronium according to claim 1, characterized in that The orthopositronium undergoes 3γ annihilation, further including: in biological tissue, a β+-radioactive isotope drug emits positrons, and the positrons combine with electrons in the organism to form orthopositronium and then undergo 3γ annihilation; At this time, the method further includes: Count the three-dimensional spatial distribution N(x, y, z) of the annihilation point corresponding to the orthopositronium to form a positron emission tomography image.

6. The method for locating the annihilation point of orthopositronium according to any one of claims 1-5, characterized in that, The position-sensitive detector adopts a flat plate wrapping structure composed of 3 position-sensitive detection units, forming a detection area covering a transverse 2π detection solid angle perpendicular to the orthopositronium beam and a radial annihilation position parallel to the orthopositronium beam.

7. The method for locating the annihilation point of orthopositronium according to any one of claims 1-5, characterized in that, The position-sensitive detector adopts an annular columnar structure, forming a 2π detection solid angle covering the x and y axis directions and a detection area along the z-axis direction.

8. The method for locating the annihilation point of the normal positronium according to claim 1, characterized in that, The orthopositronium undergoes 3γ annihilation, further including: Orthopositronium undergoes 3γ annihilation in a sample, and the 3γ photons penetrate the sample and are detected by the position-sensitive detector; the orthopositronium is wrapped inside the position-sensitive detector; At this time, the method further includes: Calculate the average time from the generation to the annihilation of each orthopositronium respectively Among them, respectively represent the distances between the annihilation point A and the incident positions S1, S2, and S3 of the three annihilation photons γ1, γ2, and γ3; among them, T1, T2, and T3 respectively represent the incident times of the three annihilation photons γ1, γ2, and γ3; c represents the propagation speed of light; Statistically analyze the average time distribution of each normal positronium from generation to annihilation Obtain the positronium annihilation lifetime spectrum.

9. The method for locating the annihilation point of the normal positronium according to claim 8, characterized in that, The position-sensitive detector adopts a hexahedron structure, forming a detection area with a 4π detection solid angle.

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