A fast absolute measurement method for TDCR to determine Birk factor

Abstract

The present invention discloses a method for rapidly determining the Birk factor, TDCR, and absolute measurement. The method comprises: preparing a radioactive sample source with a known activity A for a scintillation fluid system whose Birk factor is to be determined, injecting the sample into a scintillation vial, and placing the vial in a liquid scintillation spectrometer; initializing the Birk factor value, constructing a detection efficiency relationship for three PMTs, sequentially changing the distance between the PMT focusing electrode and the scintillation fluid to change the detection efficiency and quenching indicator parameter; iteratively optimizing the Birk factor using the detection efficiency relationship, determining the optimal Birk factor and corresponding efficiency value, and completing the measurement. The method for rapidly determining the Birk factor, provided by the present invention, can rapidly complete the calibration of such scintillation fluids, facilitating subsequent absolute measurement, and greatly improving the convenience and accuracy of the absolute measurement method.

Description

Technical Field

[0001] The present invention relates to the technical field of radioactivity measurement, and in particular to a TDCR absolute measurement method for rapidly determining a Birk factor. Background Art

[0002] Liquid scintillation spectrometers (also known as liquid scintillation counters) are widely used in customs, nuclear power plants, the nuclear industry, environmental monitoring, nuclear medicine, life science research, and radiation protection. They are primarily used to measure the activity of low-energy beta radionuclides such as H-3 and C-14. They consist of a detector, a multi-channel pulse amplitude analyzer, a high-voltage module, a transmission device, a shielding system, and a computer. They count the sample nuclear pulse signals captured by the detector in separate channels, ultimately generating a beta spectrum.

[0003] The triple-to-double coincidence ratio (TDCR) method is an absolute measurement method used in liquid scintillation spectrometers. Based on a free parameter model, it uses experimentally measured coincidence counts and a theoretical efficiency calculation model to directly determine the activity of the radioactive sample being measured. The TDCR method, developed based on coincidence counting technology, is a quenching indicator parameter that can be used to characterize changes in the quenching degree of a sample. It has the advantages of a unique quenching curve shape, good stability, and few influencing factors. The specific calculation formula is as follows:

[0004]

[0005] Wherein, Nt is the coincidence counting rate of the three-tube sample, and Nd is the coincidence counting rate of the two-tube sample.

[0006] In the free parameter model described above, a radionuclide generates a monoenergetic electron with energy E in the scintillation fluid. Part of the electron's energy excites the scintillation fluid and is converted into photon energy, while the remaining energy is lost due to chemical or color quenching. This results in a nonlinear relationship between the energy ultimately converted into effective fluorescence and the electron's initial energy. To determine the relationship between the energy deposited in the scintillation fluid and the energy of the generated photon, the following Birk ionization quenching energy function can be used:

[0007]

[0008] Among them, k B is the Birk factor, and dE / dx is the electron stopping power of the scintillation fluid, which can be calculated using the following Bethe-Block formula:

[0009]

[0010] Where c is the speed of light, N is the number of atoms per unit volume in the stopping medium, I is the average ionization potential of the medium atoms, β is v / c, and m0 is the rest mass of the electron;

[0011] However, when using a free parameter model, how to accurately determine the Birk factor of the scintillation fluid is a difficult problem. The Birk factor is determined solely by the properties of the scintillation fluid. The Birk factors of dozens of commonly used scintillation fluid systems vary, and even a slight deviation in the Birk constant will result in a large deviation in the final efficiency calculation results.

[0012] Therefore, how to perform absolute measurement accurately and quickly is a technical problem that needs to be solved urgently. Summary of the Invention

[0013] In order to solve the shortcomings of the existing technology, the present invention provides a TDCR absolute measurement method for quickly determining the Birk factor. The method changes the distance between the PMT (photomultiplier tube) focusing electrode and the scintillation bottle to change the TDCR value and the detection efficiency, and uses the preset k B The final absolute efficiency value is obtained by the method of value, and the difference between absolute efficiency and true efficiency, TDCR value, k B The relationship between the three values ​​is used to find the optimal k B The value is used to complete the calibration of this type of scintillation liquid, which is convenient for subsequent absolute measurement.

[0014] The embodiments of the present invention provide the following solutions:

[0015] An embodiment of the present invention provides a TDCR absolute measurement method for quickly determining the Birk factor, the method comprising the following steps:

[0016] S1. For the scintillation liquid system whose Birk factor is to be determined, prepare a radioactive sample source with a known activity A, inject it into a scintillation bottle, and place it in a liquid scintillation spectrometer;

[0017] S2. Initialize the value of the Birk factor and construct the detection efficiency relationship of the three PMTs. Change the distance between the focusing electrode of the PMT and the scintillation liquid one by one to change the detection efficiency and quenching indicator parameters. Use the detection efficiency relationship to iteratively optimize the Birk factor, solve the optimal Birk factor and the corresponding efficiency value, and complete the measurement.

[0018] In an optional embodiment, the radioactive sample source in step S1 is one of H-3, C-14, Sr-90, P-32 and Cl-36.

[0019] In an optional embodiment, step S2 includes the following process:

[0020] S2.1. Setting k Biis the value of Birk factor after the i-th correction, i is initialized to 0, k B0 =0.006cm / MeV; set j to the number of times the quenching indicator parameter changes, and initialize j to 0;

[0021] S2.2. Use liquid scintillation spectrometer to measure and obtain the three-tube counting rate Nt of the radioactive sample source when the Birk factor is corrected for the i-th time and the quenching indicator parameter TDCR changes for the j-th time. ij , double tube count rate Nd ij , and the quenching indicator parameter

[0022] S2.3. Calculate the true counting efficiency Eff of the radionuclide when the Birk factor is corrected for the i-th time and the quenching indicator parameter is changed for the j-th time using the following formula: j :

[0023]

[0024] S2.4. Calculate the ionization quenching energy Q after the Birk factor is corrected for the i-th time using the following formula: i :

[0025]

[0026] Where E represents the energy generated by the nuclide of the radioactive sample source in the scintillation fluid, and dE / dx is the electron stopping power of the scintillation fluid, which is calculated using the following formula:

[0027]

[0028] Where c is the speed of light, N is the number of atoms per unit volume in the scintillation fluid, I is the average ionization potential of the medium atoms, β is v / c, m0 is the electron rest mass, z is the charge number of the ray particle, Z is the average atomic number of the stopping medium, and v is the velocity of the charged particle;

[0029] S2.5. Based on the different detection efficiencies of the three PMTs in the liquid scintillation spectrometer, the following relationship holds:

[0030]

[0031] Among them, λ A ,λ B and λ C are the free parameters of the three PMTs of the liquid scintillation spectrometer; E max is the maximum energy of β particles emitted by the nuclide in the radioactive sample source, which is determined by the nuclide type. S(E) is the normalized β energy spectrum distribution calculated by Fermi theory and is calculated by the following formula:

[0032]

[0033] S2.6. Using the TDCR measurement principle, obtain the pairwise coincidence count rate N of the three PMTs in the liquid scintillation spectrometer's time coincidence circuit. AB 、N BC and N AC , N AB 、N BC and N A C logical addition to obtain the logical sum value N d , establish the objective function:

[0034]

[0035] Among them, η D is the total counting efficiency of the two tubes, η T is the total counting efficiency of the three tubes, η AB ,η BC and η AC The pairwise coincidence counting efficiencies of the three PMTs are shown;

[0036] The Levenberg-Marquardt method is used for optimization calculation to obtain the minimum λ A ,λ B and λ C The value of λ A ,λ B and λ C The total counting efficiency η of the two tubes when the Birk factor is corrected for the i-th time and the quenching indicator parameter TDCR is changed for the j-th time is calculated. Dij ;

[0037] S2.7. Calculate the relative difference in efficiency when the Birk factor is corrected for the i-th time and the quenching indicator parameter TDCR is changed for the j-th time using the following formula:

[0038]

[0039] S2.8. If j < s, execute S2.9; otherwise, execute S2.10, where s is the preset number of linear fitting data sets.

[0040] S2.9, by changing the distance between the PMT focusing electrode and the scintillation bottle, the degree of quenching is changed, that is, TDCR ij A change occurs, and j is accumulated by 1, and the process returns to step S2.2;

[0041] S2.10, group s With TDCR ij Perform linear fitting to obtain a set of slope values;

[0042] S2.11. If 0≤i<t, proceed to step S2.12; otherwise proceed to step S2.13, where t is the preset number of iterations.

[0043] S2.12, add 1 to i and set k Bi =k B0 +i×μ, where μ is the preset iteration step size, and return to step S2.2;

[0044] S2.13. Let m be the value of i when the slope is minimum, m∈[0,t], then the optimal Birk factor k B =k Bm , the optimal efficiency value is η Dm0 .

[0045] In an optional embodiment, the range of s in step S2.8 is 5-10.

[0046] In an optional embodiment, the range of t in step S2.11 is 20-50.

[0047] In an optional embodiment, the range of μ in step S2.12 is 0.0001 to 0.001.

[0048] In an optional embodiment, step S2 utilizes a PMT focusing electrode position moving device to sequentially change the distance between the focusing electrode of the PMT and the scintillation fluid.

[0049] In an optional embodiment, the PMT focusing electrode position moving device includes a sleeve arranged outside the main probe of the liquid scintillation spectrometer, the front end of the sleeve is communicated with the sample chamber of the liquid scintillation spectrometer, the end of the sleeve is provided with a compression spring, and the sleeve wall of the sleeve is provided with a stepping motor for driving the axial movement of the main probe.

[0050] In an optional embodiment, the stepper motor is mounted on the wall of the barrel through a mounting plate, and the stepper motor is connected to the main probe through a rack transmission device.

[0051] In an optional embodiment, the rack transmission device includes a driving gear connected to the rotating shaft of the stepping motor, a rack fixedly connected to the main probe, and a transfer gear meshing with the driving gear and the rack.

[0052] The beneficial effects of the present invention based on its technical solution are:

[0053] The present invention provides a TDCR absolute measurement method for quickly determining the Birk factor, which changes the TDCR value and detection efficiency by changing the distance between the PMT focusing electrode and the scintillation bottle, and uses a preset k B The final absolute efficiency value is obtained by the method of value, and the difference between absolute efficiency and true efficiency, TDCR value, kB The relationship between the three values ​​is used to find the optimal k B The value is obtained by calibrating the scintillation fluid, which is convenient for subsequent absolute measurement and greatly improves the convenience and accuracy of the absolute measurement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 A schematic flow chart of a TDCR absolute measurement method for rapidly determining the Birk factor provided by the present invention.

[0056] Figure 2 Schematic diagram of linear fitting in the embodiment.

[0057] Figure 3 Schematic diagram of the three-dimensional structure of the PMT focusing electrode position moving device in the embodiment.

[0058] Figure 4 Schematic diagram of the cross-sectional structure of the PMT focusing electrode position moving device in the embodiment.

[0059] In the figure: 1-main probe, 2-cylinder sleeve, 3-sample bottle, 4-compression spring, 5-spring cylinder, 6-stepping motor, 7-mounting plate, 8-driving gear, 9-rack, 10-transfer gear. DETAILED DESCRIPTION

[0060] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field fall within the scope of protection of the embodiments of the present invention.

[0061] Reference Figure 1 The embodiment of the present invention provides a TDCR absolute measurement method for quickly determining the Birk factor, the method comprising the following steps:

[0062] S1. For the scintillation liquid system whose Birk factor is to be determined, prepare a radioactive sample source with a known activity A (such as H-3, C-14, Sr-90, P-32, Cl-36, etc.), inject it into a scintillation bottle, and place it in a liquid scintillation spectrometer;

[0063] S2. Initialize the Birk factor value, construct the detection efficiency relationship of the three PMTs, gradually change the distance between the PMT focusing electrode and the scintillation liquid to change the detection efficiency and quenching indicator parameters, and use the detection efficiency relationship to iteratively optimize the Birk factor to solve the optimal Birk factor and corresponding efficiency value to complete the measurement. The specific process includes the following:

[0064] S2.1. Setting k Bi is the value of Birk factor after the i-th correction, i is initialized to 0, k B0 =0.006cm / MeV; set j to the number of times the quenching indicator parameter changes, and initialize j to 0;

[0065] S2.2. Use liquid scintillation spectrometer to measure and obtain the three-tube counting rate Nt of the radioactive sample source when the Birk factor is corrected for the i-th time and the quenching indicator parameter TDCR changes for the j-th time. ij , double tube count rate Nd ij , and the quenching indicator parameter

[0066] S2.3. Calculate the true counting efficiency Eff of the radionuclide when the Birk factor is corrected for the i-th time and the quenching indicator parameter is changed for the j-th time using the following formula: j :

[0067]

[0068] S2.4. Calculate the ionization quenching energy Q after the Birk factor is corrected for the i-th time using the following formula: i :

[0069]

[0070] Where E represents the energy generated by the nuclide of the radioactive sample source in the scintillation fluid, and dE / dx is the electron stopping power of the scintillation fluid, which is calculated using the following formula:

[0071]

[0072] Where c is the speed of light, N is the number of atoms per unit volume in the scintillation fluid, I is the average ionization potential of the medium atoms, β is v / c, m0 is the electron rest mass, z is the charge number of the ray particle, Z is the average atomic number of the stopping medium, and v is the velocity of the charged particle;

[0073] S2.5. Based on the different detection efficiencies of the three PMTs in the liquid scintillation spectrometer, the following relationship holds:

[0074]

[0075] Among them, λA ,λ B and λ C are the free parameters of the three PMTs of the liquid scintillation spectrometer; E max is the maximum energy of β particles emitted by the nuclide in the radioactive sample source, which is determined by the nuclide type. S(E) is the normalized β energy spectrum distribution calculated by Fermi theory and is calculated by the following formula:

[0076]

[0077] S2.6. Using the TDCR measurement principle, obtain the pairwise coincidence count rate N of the time coincidence circuit of the three PMTs (i.e., tube A, tube B, and tube C) of the liquid scintillation spectrometer. AB 、N BC and N AC , N AB 、N BC and N A C logical addition to obtain the logical sum value N d , establish the objective function:

[0078]

[0079] Among them, η D is the total counting efficiency of the two tubes, η T is the total counting efficiency of the three tubes, η AB is the counting efficiency of tubes A and B, η BC The counting efficiency of tubes B and C is η AC Tubes A and C meet the counting efficiency.

[0080] The Levenberg-Marquardt method is used for optimization calculation to obtain the minimum λ A ,λ B and λ C The value of λ A ,λ B and λ C The total counting efficiency η of the two tubes when the Birk factor is corrected for the i-th time and the quenching indicator parameter TDCR is changed for the j-th time is calculated. Dij ;

[0081] S2.7. Calculate the relative difference in efficiency when the Birk factor is corrected for the i-th time and the quenching indicator parameter TDCR is changed for the j-th time using the following formula:

[0082]

[0083] S2.8. If j < s, execute S2.9; otherwise, execute S2.10, where s is the preset number of linear fitting data sets. In this embodiment, s = 5.

[0084] S2.9, by changing the distance between the PMT focusing electrode and the scintillation bottle, the degree of quenching is changed, that is, TDCR ij A change occurs, and j is accumulated by 1, and the process returns to step S2.2;

[0085] S2.10, such as Figure 2 As shown, group s With TDCR ij Perform linear fitting to obtain a set of slope values;

[0086] S2.11. If 0≤i<t, proceed to step S2.12; otherwise proceed to step S2.13, where t is the preset number of iterations, and in this embodiment, t=20;

[0087] S2.12, add 1 to i and set k Bi =k B0 +i×μ, where μ is the preset iteration step size, which is set to 0.0005 in this embodiment, and then returns to step S2.2;

[0088] S2.13. Let m be the value of i when the slope is minimum, m∈[0,t], then the optimal Birk factor k B =k Bm , the optimal efficiency value is η Dm0 .

[0089] η can be easily calculated later AB ,η BC ,η AC ,η T and η D , through Nd and η D The activity of the sample is obtained using the relationship.

[0090] Reference Figure 3 and Figure 4 In step S2 of this embodiment, the distance between the focusing electrode of the PMT and the scintillation liquid is changed successively by using the PMT focusing electrode position moving device.

[0091] The PMT focus position moving device comprises a sleeve 2, which can be made of copper and is mounted over the main probe 1 of a liquid scintillation spectrometer. The front end of the sleeve communicates with the sample chamber of the liquid scintillation spectrometer, with the main probe facing a sample bottle 3. A compression spring 4 is mounted on the end of the sleeve, which is enclosed by a spring cylinder 5. A stepper motor 6 is mounted within the sleeve wall to drive the axial movement of the main probe.

[0092] The stepper motor is mounted on the wall of the barrel through a mounting plate 7, and the stepper motor is connected to the main probe through a rack transmission device.

[0093] The rack transmission device includes a driving gear 8 connected to the rotating shaft of the stepping motor, a rack 9 fixedly connected to the main probe, and a transfer gear 10 meshing with the driving gear and the rack.

[0094] During the measurement process, the PMT of the main probe is fixed as a whole in the barrel sleeve. A compression spring ensures that the PMT end window is closest to the scintillation bottle in the normal position. When the position needs to be changed, a small stepper motor drives the rack to move the barrel sleeve and PMT outward as a whole, so that the distance between the PMT focusing electrode and the scintillation bottle is increased, and the detection efficiency and TDCR are changed.

[0095] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0096] The present invention is described with reference to flowcharts and / or block diagrams of methods, apparatus (modules, systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded computer, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0097] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0098] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0099] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0100] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A TDCR absolute measurement method for rapidly determining the Birk factor, characterized in that: The method comprises the following steps: S1. For the scintillation liquid system whose Birk factor is to be determined, prepare a radioactive sample source with a known activity A, inject it into a scintillation bottle, and place it in a liquid scintillation spectrometer; S2. Initialize the value of the Birk factor and construct the detection efficiency relationship of the three PMTs. Change the distance between the focusing electrode of the PMT and the scintillation liquid one by one to change the detection efficiency and quenching indicator parameters. Use the detection efficiency relationship to iteratively optimize the Birk factor, solve the optimal Birk factor and the corresponding efficiency value, and complete the measurement.

2. The TDCR absolute measurement method for rapidly determining the Birk factor according to claim 1, characterized in that: The radioactive sample source in step S1 is one of H-3, C-14, Sr-90, P-32 and Cl-36.

3. The TDCR absolute measurement method for rapidly determining the Birk factor according to claim 1, characterized in that: Step S2 includes the following process: S2.

1. Settings k Bi Birk factor i The corrected value is initialized i is 0, k B0 =0.006cm / MeV; set up j The number of times the quenching indicator parameter changes, initialize j is 0; S2.

2. Use liquid scintillation spectrometer to measure and obtain the three-tube counting rate of the radioactive sample source when the Birk factor is corrected for the i-th time and the quenching indicator parameter TDCR changes for the j-th time. Nt ij , double tube count rate Nd ij , and the quenching indicator parameter ; S2.

3. Calculate the Birk factor by the following formula i The first correction and quenching indication parameter j The true counting efficiency of radionuclides changes Eff ij : ； S2.

4. Calculate the Birk factor by the following formula i Corrected ionization quenching energy Q i : ， in, E It indicates the energy produced by the nuclide of the radioactive sample source in the scintillation fluid. dE / dx is the electron stopping power of the scintillation fluid, which is calculated using the following formula: ， Where c is the speed of light, N is the number of atoms per unit volume in the scintillation fluid, I is the average ionization potential of the medium atoms, β is v / c, m0 is the electron rest mass, z is the charge number of the ray particle, Z is the average atomic number of the stopping medium, and v is the velocity of the charged particle; S2.

5. Based on the different detection efficiencies of the three PMTs in the liquid scintillation spectrometer, the following relationship holds: ， ， ， Among them, λ A ,λ B and λ C are the free parameters of the three PMTs of the liquid scintillation spectrometer; E max is the maximum energy of β particles emitted by the nuclide in the radioactive sample source, which is determined by the nuclide type. S(E) is the normalized β energy spectrum distribution calculated by Fermi theory and is calculated by the following formula: ； S2.

6. Using the TDCR measurement principle, obtain the pairwise coincidence count rate N of the three PMTs in the liquid scintillation spectrometer's time coincidence circuit. AB 、N BC and N AC , N AB 、N BC and N A C logical addition to obtain the logical sum value N t , establish the objective function: ， in, η D For the two tubes to meet the total counting efficiency, η T For the three tubes, the total counting efficiency is η AB 、 η BC and η AC The pairwise coincidence counting efficiencies of the three PMTs are shown; The Levenberg-Marquardt method is used for optimization calculation to obtain the minimum λ A ,λ B and λ C The value of λ A ,λ B and λ C The total counting efficiency of the two tubes when the Birk factor is corrected for the i-th time and the quenching indicator parameter TDCR is changed for the j-th time is calculated. η Dij ; S2.

7. Calculate the relative difference in efficiency when the Birk factor is corrected for the i-th time and the quenching indicator parameter TDCR is changed for the j-th time using the following formula: φ ij : ； S2.8, if j< s , then execute S2.9, otherwise execute S2.10, s is the preset number of linear fitting data sets; S2.9, by changing the distance between the PMT focusing electrode and the scintillation bottle, the degree of quenching is changed, that is, TDCR ij changes and makes j Add 1 and return to step S2.2; S2.10, s Group φ ij and TDCR ij Perform linear fitting to obtain a set of slope values; S2.11, if 0≤ i < t , then execute step S2.12, otherwise proceed to step S2.13, where t is the preset number of iterations; S2.12, make i Accumulate 1 and make k Bi = k B0 + i × μ , μ is the preset iteration step, and returns to step S2.2; S2.13, set m When the slope value is minimum i The value of m ∈[0, t ], then the optimal Birk factor k B = k Bm , the optimal efficiency value is η Dm0 .

4. The TDCR absolute measurement method for rapidly determining the Birk factor according to claim 3, characterized in that: In step S2.8 s The range is 5~10.

5. The TDCR absolute measurement method for rapidly determining the Birk factor according to claim 3, characterized in that: In step S2.11 t The range is 20~50.

6. The TDCR absolute measurement method for rapidly determining the Birk factor according to claim 3, characterized in that: In step S2.12 μ The range is 0.0001~0.

001.

7. The TDCR absolute measurement method for rapidly determining the Birk factor according to claim 3, characterized in that: In step S2, the distance between the PMT focusing electrode and the scintillating liquid is changed successively by using the PMT focusing electrode position moving device.

8. The TDCR absolute measurement method for rapidly determining the Birk factor according to claim 7, characterized in that: The PMT focusing electrode position moving device includes a sleeve mounted outside the main probe of the liquid scintillation spectrometer, the front end of the sleeve is connected to the sample chamber of the liquid scintillation spectrometer, the end of the sleeve is provided with a compression spring, and the sleeve wall of the sleeve is provided with a stepping motor for driving the main probe to move axially.

9. The TDCR absolute measurement method for rapidly determining the Birk factor according to claim 8, characterized in that: The stepper motor is mounted on the wall of the barrel through a mounting plate, and the stepper motor is connected to the main probe through a rack transmission device.

10. The TDCR absolute measurement method for rapidly determining the Birk factor according to claim 9, characterized in that: The rack transmission device includes a driving gear connected to the rotating shaft of the stepping motor, a rack fixedly connected to the main probe, and a transfer gear meshing with the driving gear and the rack.

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