Anti-coincidence ultralow background gamma spectrometer

Abstract

The invention relates to an anticoincidence ultralow background gamma spectrometer which comprises a lead chamber assembly serving as a sample chamber, and the lead chamber assembly comprises an outer layer shielding lead chamber, an inner layer shielding lead ring, an outer layer shielding lead ring and an inner layer shielding lead ring, the outer-layer shielding lead chamber adopts a three-section segmented structure; the inner layer shielding lead ring adopts a four-section type segmented structure; an annular plastic scintillator detector is arranged between the outer-layer shielding lead chamber and the inner-layer shielding lead ring; a cadmium plate is arranged between the annular plastic scintillator detector and the inner layer shielding lead ring; the inner layer shielding lead ring is sleeved on the outer surface of the copper lining; an HPGe detector is arranged in the copper lining; the inner cavity of the copper lining is further communicated with the atmosphere through an exhaust hose. And the HPGe detector is communicated with the Dewar flask through a pipeline. Compared with a common substance-shielded low-background HPGe gamma spectrometer, the detection sensitivity of the low-background HPGe gamma spectrometer is remarkably improved, the 50-2000 Kev integral background is reduced by more than one order of magnitude after anti-coincidence is adopted, and meanwhile, the low-background HPGe gamma spectrometer has extremely low natural nuclide gamma ray peak background.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear radiation detection, in particular to an anti-coincidence ultra-low background gamma spectrometer. Background Art

[0002] Spectrometers are widely used in routine radioactivity measurements and basic scientific research (such as gamma spectrometers). The background level of the spectrometer is one of the important factors affecting its detection limit. In many cases, the background level of the spectrometer should be reduced as much as possible to enable the spectrometer to reach a lower detection limit.

[0003] HPGe γ spectrometer is a γ spectrometer with HPGe (high purity germanium) as the main detector. The main sources of its background include:

[0004] Soft components of cosmic rays, such as cosmic rays composed of some particle flows from space entering the Earth's atmosphere and their secondary products;

[0005] The natural radioactive background in the surrounding environment, such as radioactive isotopes in shielding materials and detection sources, and introduced radioactive impurities or contamination.

[0006] Material shielding is usually used for the soft components of cosmic rays and the natural radioactive background of the surrounding environment. Considering the price, atomic number and mechanical properties, lead is the best shielding material. In order to achieve a better shielding effect, an integrated lead chamber is generally used as the shielding chamber, and a large amount of lead is used. Since lead is a metal material with a high density, the mass of the shielding chamber is also large, which makes the transportation and installation of the shielding chamber more troublesome. For example: using an integrated lead chamber with a wall thickness of about 15cm as a shielding chamber can shield the soft components of cosmic rays and the natural radioactive background of the surrounding environment, but the level of background reduction is limited. The best level of the integrated background in the 50keV-2000keV energy zone is 1s -1 The relative efficiency of the HPGe detector is about 40%, and the overall weight of the HPGe γ spectrometer is large, which is inconvenient to transport and install.

[0007] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0008] In view of the defects existing in the prior art, the purpose of the present invention is to provide an anti-coincidence ultra-low background gamma spectrometer, which has significantly improved detection sensitivity compared with the low background HPGe gamma spectrometer with ordinary material shielding, and the 50Kev-2000Kev integral background is reduced by more than one order of magnitude after anti-coincidence, and at the same time has an extremely low natural nuclide gamma ray peak background.

[0009] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0010] An anti-coincidence ultra-low background gamma spectrometer, characterized in that it comprises: a lead chamber assembly 19 as a sample chamber, the lead chamber assembly 19 comprising: an outer shielding lead chamber 6, in which an inner shielding lead ring 3 is arranged;

[0011] The outer shielding lead chamber 6 adopts a segmented structure, which is formed by stacking three segments from top to bottom;

[0012] The inner shielding lead ring 3 adopts a segmented structure, which is formed by four segments stacked from top to bottom;

[0013] An annular plastic scintillator detector 5 is provided between the outer shielding lead chamber 6 and the inner shielding lead ring 3;

[0014] A cadmium plate 4 is provided between the annular plastic scintillator detector 5 and the inner shielding lead ring 3;

[0015] The inner shielding lead ring 3 is sleeved on the outer surface of the copper lining 2;

[0016] A HPGe detector 1 is provided in the copper lining 2;

[0017] The inner cavity of the copper liner 2 is also connected to the atmosphere through an exhaust hose 24;

[0018] The HPGe detector 1 is connected to the Dewar flask 13 through a pipeline.

[0019] On the basis of the above technical solution, the lead chamber assembly 19 is arranged in the bracket assembly 16;

[0020] The Dewar flask 13 is disposed in the support assembly 16 and is located outside the sample chamber. A Dewar flask support 21 is disposed between the bottom surface of the Dewar flask 13 and the support assembly 16 .

[0021] On the basis of the above technical solution, the outer shielding lead chamber 6 comprises a third outer shielding lead chamber 6-3, a second outer shielding lead chamber 6-2 and a first outer shielding lead chamber 6-1 stacked in sequence from top to bottom; the components of the outer shielding lead chamber 6 are positioned and installed by stoppers;

[0022] The inner shielding lead ring 3 includes a fourth inner shielding lead ring 3-4, a third inner shielding lead ring 3-3, a second inner shielding lead ring 3-2, and a first inner shielding lead ring 3-1 which are stacked in sequence from top to bottom; the components of the inner shielding lead ring 3 are positioned and installed by stoppers;

[0023] The first inner shielding lead ring 3-1 is composed of two parts of equal weight, the inner lead ring 3-1-1 and the outer lead ring 3-1-2.

[0024] On the basis of the above technical solution, the lead shielding thickness of the outer shielding lead chamber 6 is 100mm, and the old lead used for many years is used;

[0025] The lead shielding thickness of the inner shielding lead ring 3 is 90mm, and it is made of old lead. 210 Pb (lead-210) content ≤ 25Bq / kg.

[0026] On the basis of the above technical solution, the interior of the inner shielding lead ring 3 is provided with an oxygen-free copper plate installed in a 4π surround, and the thickness of the oxygen-free copper plate is 6 mm.

[0027] On the basis of the above technical solution, it also includes: a mounting base 25, on which an outer shielding room bottom assembly 26 is centrally arranged;

[0028] The outer shielding chamber bottom assembly 26 is provided with eight photomultiplier tube mounting holes;

[0029] The HPGe detector 1 is centrally fixed on the outer shielding room bottom assembly 26 , and the pipeline connecting the HPGe detector 1 and the Dewar flask 13 is buried in the outer shielding room bottom assembly 26 .

[0030] On the basis of the above technical solution, it also includes: a lead core 27, the lead core 27 is divided into a first lead core 27-1 and a second lead core 27-2;

[0031] The first lead core 27-1 is installed in the inner hole of the inner lead ring 3-1-1 and fixed on the outer shielding room bottom assembly 26. A reserved installation hole for the HPGe detector 1 is provided in the center of the lead core 27-1;

[0032] The second lead core 27-2 is installed in the inner hole of the outer lead ring 3-1-2 and fixed on the outer shielding room bottom assembly 26.

[0033] On the basis of the above technical solution, the annular plastic scintillator detector 5 has an outer dimension of φ600×φ400×550 mm and a capacity of 132 L.

[0034] On the basis of the above technical solution, the lead chamber assembly 19 adopts an upper opening structure, and a support cover assembly 18 driven by a hydraulic transmission device is provided at the opening;

[0035] The bracket cover assembly 18 includes:

[0036] A cover copper plate 12 is used to seal the opening at the upper end of the copper lining 2;

[0037] The cover copper plate 12 is filled with the cover inner layer lead shield 11;

[0038] The copper cover plate 12 is centrally fixed on the lower surface of the cadmium cover plate 10;

[0039] A circular plastic scintillator detector 8 is fixed on the upper surface of the cadmium cover plate 10, and the circular plastic scintillator detector 8 is equipped with eight photomultiplier tubes 7;

[0040] The outer lead shield 9 of the cover is used to seal the circular plastic scintillator detector 8 on the upper surface of the cover cadmium plate 10.

[0041] On the basis of the above technical solution, the hydraulic transmission device comprises:

[0042] The translation cylinder mounting seat 15 is fixed on the top of the bracket assembly 16;

[0043] The translation cylinder 23 is mounted on the translation cylinder mounting seat 15, the translation cylinder piston rod faces the lead chamber assembly 19, and the free end of the translation cylinder piston rod is connected to the roller assembly 14;

[0044] A running rail adapted to the roller assembly 14 is provided on the top of the bracket assembly 16;

[0045] A lifting hydraulic cylinder 22 is provided on the roller assembly 14 , and a piston rod of the lifting hydraulic cylinder is vertically arranged downward, and a free end of the piston rod of the lifting hydraulic cylinder is connected to the bracket cover assembly 18 .

[0046] The anti-coincidence ultra-low background gamma spectrometer described in the present invention has the following beneficial effects:

[0047] 1. The combination of material shielding and anti-coincidence shielding can significantly reduce the background level;

[0048] An annular plastic scintillator detector is installed between the outer shielding lead chamber and the inner shielding lead ring, and a circular plastic scintillator detector is installed on the upper cover;

[0049] Install the lead chamber assembly as a sample chamber in parallel with the Dewar flask, and connect the sample chamber and the Dewar flask through a hose;

[0050] Material shielding can effectively block the soft components of cosmic rays and the natural radioactive background of the surrounding environment;

[0051] Two plastic scintillators, annular and circular, are used as anti-coincidence detectors, and anti-coincidence technology is used to significantly reduce the background of secondary cosmic rays.

[0052] The structural design combining material shielding with anti-coincidence shielding of two plastic scintillator detectors can reduce the 50Kev-2000Kev integral background by more than one order of magnitude, and at the same time has an extremely low natural nuclide gamma-ray peak background, making the system's minimum monitoring limit reach below 0.1Bq / kg;

[0053] 2. In order to solve the problem that the spectrometer is heavy and difficult to transport and install, a segmented structure design is adopted to facilitate transportation and installation;

[0054] The outer shielding lead chamber 6 adopts a segmented structure, which is formed by stacking three segments from top to bottom;

[0055] The inner shielding lead ring 3 adopts a segmented structure, which is formed by four segments stacked from top to bottom;

[0056] 3. In order to solve the problem that the lead chamber cover is too heavy and inconvenient for testing, the lead chamber switch door adopts a hydraulic transmission system, which has the advantages of large load, stable operation, low noise, convenient debugging and easy operation;

[0057] The hydraulic transmission system adopts PLC programmable logic controller control and can run semi-automatically, which is convenient for testing work and has the advantages of reliable operation, easy adjustment, and stereotyped automatic operation.

[0058] 4. In view of the influence of radon gas in the air of the sample room on the background, a strict sample room surrounded by a copper lining 2 and a copper cover 12 is provided. A small hole is provided at the bottom of the sample room. A hose is used to connect the small hole below the sample room. The naturally evaporated nitrogen in the Dewar flask directly enters the sample room through the hose, expelling the air in the sample room and avoiding the influence of radon gas in the air on the background;

[0059] 5. In view of the waste of nitrogen resources caused by natural evaporation of the Dewar flask, a hose is used to connect the small hole at the bottom of the sample chamber, so that the naturally evaporated nitrogen in the Dewar flask can be directly filled into the sample chamber.

[0060] The anti-coincidence ultra-low background gamma spectrometer disclosed by the present invention has a reasonable overall design, a compact structure, and is economical and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention has the following accompanying drawings:

[0062] The accompanying drawings are used to better understand the present invention and do not constitute an improper limitation of the present invention.

[0063] Figure 1 A schematic structural diagram of an anti-coincidence ultra-low background gamma spectrometer described in the present invention.

[0064] Figure 2 A schematic structural diagram of a sample chamber of an anti-coincidence ultra-low background gamma spectrometer according to the present invention.

[0065] Figure 3 Schematic diagram of the split structure of the lead chamber of the anti-coincidence ultra-low background gamma spectrometer described in the present invention Figure 1 .

[0066] Figure 4 Schematic diagram of the split structure of the lead chamber of the anti-coincidence ultra-low background gamma spectrometer described in the present invention Figure 2 . DETAILED DESCRIPTION

[0067] The present invention is further described in detail below in conjunction with the accompanying drawings. The detailed description is an explanation made in conjunction with the exemplary embodiments of the present invention, including various details of the embodiments of the present invention to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those skilled in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for the sake of clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0068] like Figure 1 , Figure 2 , Figure 3 , Figure 4 As shown, the present invention provides an anti-coincidence ultra-low background gamma spectrometer, comprising: a lead chamber assembly 19 as a sample chamber, arranged in a bracket assembly 16;

[0069] The lead chamber assembly 19 comprises: an outer shielding lead chamber 6, in which an inner shielding lead ring 3 is arranged;

[0070] The outer shielding lead chamber 6 comprises a third outer shielding lead chamber 6-3, a second outer shielding lead chamber 6-2 and a first outer shielding lead chamber 6-1 which are stacked in sequence from top to bottom; the outer shielding lead chamber 6 adopts a segmented structure, which is formed by stacking three segments from top to bottom; the segmented structure is more convenient for the transportation and installation of the spectrometer; the components of the outer shielding lead chamber 6 are positioned and installed by stoppers, without the need for bolt fixing;

[0071] The inner shielding lead ring 3 includes a fourth inner shielding lead ring 3-4, a third inner shielding lead ring 3-3, a second inner shielding lead ring 3-2, and a first inner shielding lead ring 3-1 which are stacked in sequence from top to bottom; the inner shielding lead ring 3 adopts a segmented structure, which is formed by four segments stacked from top to bottom; as mentioned above, the segmented structure is more convenient for the transportation and installation of the spectrometer; the components of the inner shielding lead ring 3 are positioned and installed by stoppers, without the need for bolt fixation;

[0072] An annular plastic scintillator detector 5 is provided between the outer shielding lead chamber 6 and the inner shielding lead ring 3;

[0073] A cadmium plate 4 is provided between the annular plastic scintillator detector 5 and the inner shielding lead ring 3; the cadmium plate 4 is used to increase the composite shielding effect, and the thickness of the cadmium plate 4 is 1 mm;

[0074] The inner shielding lead ring 3 is sleeved on the outer surface of the copper lining 2; the screen wall thickness of the copper lining 2 is 6mm;

[0075] A HPGe detector 1 is provided in the copper lining 2;

[0076] The inner cavity of the copper liner 2 is also connected to the atmosphere through an exhaust hose 24; the exhaust hose 24 is used to discharge the air in the inner cavity of the copper liner 2;

[0077] The HPGe detector 1 is connected to a Dewar flask 13 through a pipeline. The Dewar flask 13 is disposed in a support assembly 16 and is located outside the sample chamber. A Dewar flask support 21 is disposed between the bottom surface of the Dewar flask 13 and the support assembly 16 .

[0078] Through multi-layer shielding and anti-coincidence technology, this embodiment achieves an ultra-low background radiation level and improves the detection capability of weak signals; the segmented shielding structure design makes the spectrometer easier to transport and install, and adapts to different usage environments; this design improves the measurement accuracy and sensitivity of the gamma spectrometer, and is particularly suitable for occasions requiring high sensitivity and low background radiation levels, such as environmental monitoring, nuclear material analysis, and scientific research.

[0079] On the basis of the above technical solution, the support assembly 16 is provided with a plurality of feet 17 .

[0080] On the basis of the above technical solution, the lead shielding thickness of the outer shielding lead chamber 6 is 100 mm, and the weight of each section is not more than 570 kg;

[0081] The lead shielding thickness of the inner shielding lead ring 3 is 90mm, the weight of the fourth inner shielding lead ring 3-4 is 135kg, the weight of the third inner shielding lead ring 3-3 is 142kg, the weight of the second inner shielding lead ring 3-2 is 137kg, the weight of the first inner shielding lead ring 3-1 is 102kg, and the first inner shielding lead ring 3-1 is composed of two parts of equal weight, the inner lead ring 3-1-1 and the outer lead ring 3-1-2;

[0082] Exemplarily, the outer shielding lead chamber 6 is made of many years of old lead, preferably primary lead;

[0083] Exemplarily, the inner shielding lead ring 3 is made of old lead for many years, preferably primary lead, to ensure its 210 Pb (lead-210) content ≤ 25Bq / kg; the old lead used in the inner shielding lead ring 3 210 The specific activity of Pb is about 1 / 10 of the original old lead in the outer shielding lead chamber.

[0084] On the basis of the above technical solution, an oxygen-free copper plate surrounded by 4π is provided inside the inner shielding lead ring 3 .

[0085] Exemplarily, the thickness of the oxygen-free copper plate is 6 mm, and the oxygen-free copper plate is used to increase the composite shielding effect and eliminate the influence of the soft components of cosmic rays and the natural radioactive background of the surrounding environment on the counting rate of the plastic scintillator detector and the background of the spectrometer.

[0086] Based on the above technical solution, Figure 3 , Figure 4 As shown, it also includes: a mounting base 25, on which an outer shielding room bottom assembly 26 is centrally disposed;

[0087] The outer shielding chamber bottom assembly 26 is provided with eight photomultiplier tube mounting holes;

[0088] The HPGe detector 1 is centrally fixed on the outer shielding room bottom assembly 26 , and the pipeline connecting the HPGe detector 1 and the Dewar flask 13 is buried in the outer shielding room bottom assembly 26 .

[0089] Based on the above technical solution, Figure 3 , Figure 4 As shown, it also includes: a lead core 27, the lead core 27 is divided into a first lead core 27-1 and a second lead core 27-2;

[0090] The first lead core 27-1 is installed in the inner hole of the inner lead ring 3-1-1 and fixed on the outer shielding room bottom assembly 26. A reserved installation hole for the HPGe detector 1 is provided in the center of the lead core 27-1;

[0091] The second lead core 27-2 is installed in the inner hole of the outer lead ring 3-1-2 and fixed on the outer shielding room bottom assembly 26.

[0092] On the basis of the above technical solution, the annular plastic scintillator detector 5 has an outer dimension of φ600×φ400×550 mm and a capacity of 132 L.

[0093] On the basis of the above technical solution, the lead chamber assembly 19 adopts an upper opening structure, and a bracket cover assembly 18 driven by a hydraulic transmission device is provided at the opening.

[0094] The hydraulic transmission device is controlled by a programmable controller PLC and can be operated semi-automatically. The bracket cover assembly 18 is used to close the opening on the upper part of the lead chamber assembly 19.

[0095] The hydraulic transmission device is equipped with a door opening and closing button.

[0096] Based on the above technical solution, Figure 1 , Figure 2 As shown, the hydraulic transmission device includes:

[0097] The translation cylinder mounting seat 15 is fixed on the top of the bracket assembly 16; Figure 1 In the illustrated embodiment, the translation cylinder mounting seat 15 is fixed to the top of the bracket assembly 16 and is adjacent to one side of the Dewar flask 13;

[0098] The translation cylinder 23 is mounted on the translation cylinder mounting seat 15, the translation cylinder piston rod faces the lead chamber assembly 19, and the free end of the translation cylinder piston rod is connected to the roller assembly 14;

[0099] A running rail adapted to the roller assembly 14 is provided on the top of the bracket assembly 16;

[0100] A lifting hydraulic cylinder 22 is provided on the roller assembly 14 , and a piston rod of the lifting hydraulic cylinder is vertically arranged downward, and a free end of the piston rod of the lifting hydraulic cylinder is connected to the bracket cover assembly 18 .

[0101] When the door opening and closing button is pressed, the lifting hydraulic cylinder 22 lifts the bracket cover assembly 18 upwards. After it is lifted into place and locked, the translation cylinder 23 moves the bracket cover assembly 18 to the side of the Dewar flask 13. After it is moved into place and locked, the action of opening the lead chamber assembly 19 is completed.

[0102] When the door opening and closing button is pressed again, the translation cylinder 23 moves the bracket cover assembly 18 to above the lead chamber assembly 19. After it is moved into place and locked, the lifting hydraulic cylinder 22 drives the bracket cover assembly 18 to descend. After it is lowered into place and locked, the action of closing the lead chamber assembly 19 is completed.

[0103] Based on the above technical solution, Figure 2 As shown, the bracket cover assembly 18 includes:

[0104] A cover copper plate 12 is used to seal the opening at the upper end of the copper lining 2;

[0105] The cover copper plate 12 is filled with the cover inner layer lead shield 11;

[0106] The copper cover plate 12 is centrally fixed on the lower surface of the cadmium cover plate 10;

[0107] A circular plastic scintillator detector 8 is fixed on the upper surface of the cadmium cover plate 10. The circular plastic scintillator detector 8 is equipped with eight photomultiplier tubes 7. The lower ends of the photomultiplier tubes 7 pass through the cadmium cover plate 10 and are inserted into the photomultiplier tube mounting holes on the outer shielding room bottom assembly 26.

[0108] The outer lead shield 9 of the cover is used to seal the circular plastic scintillator detector 8 on the upper surface of the cover cadmium plate 10.

[0109] The support cover assembly 18 cooperates with the outer shielding lead chamber 6 to achieve a better shielding effect.

[0110] On the basis of the above technical solution, the shielding thickness of the outer lead shielding 9 of the cover is 100 mm, and the screen wall thickness of the inner lead shielding 11 of the cover is 90 mm.

[0111] On the basis of the above technical solution, the circular plastic scintillator detector 8 has an outer dimension of φ600×100 mm and a volume of 28 L.

[0112] Eight photomultiplier tubes are arranged at 7 equal intervals.

[0113] On the basis of the above technical solution, the cadmium cover plate 10 is a cadmium absorption sheet with a thickness of 1 mm.

[0114] The cadmium cover plate 10 is used to reduce the background generated by the heat capture of the germanium crystal and the shielding material.

[0115] On the basis of the above technical solution, the cover copper plate 12 is an oxygen-free copper plate with a thickness of 6 mm.

[0116] The copper cover plate 12 is used to increase the composite shielding effect.

[0117] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0118] The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiment. Any equivalent modifications or changes made by those skilled in the art based on the contents disclosed by the present invention should be included in the protection scope recorded in the claims.

Claims

1. An anti-coincidence ultra-low background gamma spectrometer, characterized in that: include: A lead chamber assembly (19) serving as a sample chamber, the lead chamber assembly (19) comprising: an outer shielding lead chamber (6) in which an inner shielding lead ring (3) is arranged; The outer shielding lead chamber (6) adopts a segmented structure, which is formed by stacking three segments from top to bottom; The inner shielding lead ring (3) adopts a segmented structure, which is formed by stacking four segments from top to bottom; An annular plastic scintillator detector (5) is provided between the outer shielding lead chamber (6) and the inner shielding lead ring (3); A cadmium plate (4) is provided between the annular plastic scintillator detector (5) and the inner shielding lead ring (3); The inner shielding lead ring (3) is sleeved on the outer surface of the copper lining (2); A HPGe detector (1) is arranged in the copper lining (2); The inner cavity of the copper liner (2) is also connected to the atmosphere through an exhaust hose (24); The HPGe detector (1) is connected to the Dewar flask (13) via a pipeline.

2. The anti-coincidence ultra-low background gamma spectrometer according to claim 1, characterized in that: The lead chamber assembly (19) is arranged in the bracket assembly (16); The Dewar flask (13) is arranged in the support assembly (16) and is located outside the sample chamber. A Dewar flask support (21) is arranged between the bottom surface of the Dewar flask (13) and the support assembly (16).

3. The anti-coincidence ultra-low background gamma spectrometer according to claim 1, characterized in that: The outer shielding lead chamber (6) comprises a third outer shielding lead chamber (6-3), a second outer shielding lead chamber (6-2) and a first outer shielding lead chamber (6-1) which are stacked in sequence from top to bottom; the components of the outer shielding lead chamber (6) are positioned and installed through stoppers; The inner shielding lead ring (3) comprises a fourth inner shielding lead ring (3-4), a third inner shielding lead ring (3-3), a second inner shielding lead ring (3-2), and a first inner shielding lead ring (3-1) which are stacked in sequence from top to bottom; the components of the inner shielding lead ring (3) are positioned and installed by means of stoppers; The first inner shielding lead ring (3-1) is composed of two parts, an inner lead ring (3-1-1) and an outer lead ring (3-1-2) of equal weight.

4. The anti-coincidence ultra-low background gamma spectrometer according to claim 1, characterized in that: The lead shielding thickness of the outer shielding lead chamber (6) is 100 mm, and the lead used is old lead. The lead shielding thickness of the inner shielding lead ring (3) is 90 mm, and the old lead used is many years old. 210 Pb (lead-210) content ≤ 25Bq / kg.

5. The anti-coincidence ultra-low background gamma spectrometer according to claim 1, characterized in that: An oxygen-free copper plate which is installed in a 4π surround is arranged inside the inner shielding lead ring (3), and the thickness of the oxygen-free copper plate is 6 mm.

6. The anti-coincidence ultra-low background gamma spectrometer according to claim 3, characterized in that: It also includes: a mounting base (25) on which an outer shielding room bottom assembly (26) is centrally arranged; The outer shielding chamber bottom assembly (26) is provided with eight photomultiplier tube mounting holes; The HPGe detector (1) is centrally fixed on the outer shielding room bottom assembly (26), and the pipeline connecting the HPGe detector (1) and the Dewar flask (13) is buried in the outer shielding room bottom assembly (26).

7. The anti-coincidence ultra-low background gamma spectrometer according to claim 6, characterized in that: Also includes: A lead core (27), the lead core (27) is divided into two parts: a first lead core (27-1) and a second lead core (27-2); The first lead core (27-1) is installed in the inner hole of the inner lead ring (3-1-1) and fixed on the outer shielding room bottom assembly (26); a reserved installation hole for the HPGe detector (1) is provided in the center of the lead core (27-1); The second lead core (27-2) is installed in the inner hole of the outer lead ring (3-1-2) and is fixed on the outer shielding room bottom assembly (26).

8. The anti-coincidence ultra-low background gamma spectrometer according to claim 1, characterized in that: The annular plastic scintillator detector (5) has an outer dimension of φ600×φ400×550 mm and a capacity of 132 L.

9. The anti-coincidence ultra-low background gamma spectrometer according to claim 1, characterized in that: The lead chamber assembly (19) adopts an upper opening structure, and a support cover assembly (18) driven by a hydraulic transmission device is provided at the opening; The bracket cover assembly (18) comprises: A copper cover plate (12) for sealing the opening at the upper end of the copper lining (2); The cover copper plate (12) is filled with a cover inner layer lead shield (11); The copper cover plate (12) is centrally fixed on the lower surface of the cadmium cover plate (10); A circular plastic scintillator detector (8) is fixed on the upper surface of the cadmium cover plate (10), and the circular plastic scintillator detector (8) is equipped with eight photomultiplier tubes (7); The outer lead shield (9) of the cover is used to seal the circular plastic scintillator detector (8) on the upper surface of the cover cadmium plate (10).

10. The anti-coincidence ultra-low background gamma spectrometer according to claim 9, characterized in that: The hydraulic transmission device comprises: A translation cylinder mounting seat (15) is fixed on the top of the bracket assembly (16); The translation cylinder (23) is mounted on the translation cylinder mounting seat (15), the translation cylinder piston rod faces one side of the lead chamber assembly (19), and the free end of the translation cylinder piston rod is connected to the roller assembly (14); A running rail adapted to the roller assembly (14) is provided on the top of the bracket assembly (16); A lifting hydraulic cylinder (22) is provided on the roller assembly (14), a piston rod of the lifting hydraulic cylinder is vertically arranged downward, and a free end of the piston rod of the lifting hydraulic cylinder is connected to the bracket cover assembly (18).

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