Measuring device and measuring method for the identification of radioactive contamination

Abstract

The application discloses a measuring device for radioactive contamination identification, which comprises an upper detector group, a lower detector group, a left detector group, a right detector group, a front detector group and a rear detector group, and the upper detector group, the lower detector group, the left detector group, the right detector group, the front detector group and the rear detector group constitute a full-closed 4pi measuring chamber for measurement; each of the detector groups comprises one or more detectors; each of the detectors comprises a plastic scintillator and a photomultiplier tube; and the plastic scintillator detection surface of the detector in the lower detector group is covered with a zinc sulfide coating. The measuring device of the application adopts the 6-face staggered arrangement of the scintillator detectors, realizes the 4pi measurement without dead zone, and improves the sensitivity of the measuring device; the photomultiplier tubes of the detectors are arranged at the upper and lower ends, thereby reducing the equipment volume; and the bottom detector is provided with the zinc sulfide coating, thereby solving the defect that the traditional contamination measuring equipment cannot simultaneously measure alpha, beta and gamma.

Description

Technical Field

[0001] This invention belongs to the field of radioactive detection technology, and relates to a measuring device for identifying radioactive contamination and a measuring method for identifying radioactive contamination based on the measuring device. Background Technology

[0002] In the nuclear industry, including nuclear power plants and reprocessing plants, and in nuclear technology applications such as particle accelerators and radiopharmaceutical production, to prevent potentially radioactively contaminated objects from being taken out of the controlled area and causing radioactive contamination, small objects being carried out of the controlled area are typically tested for radioactivity at the access points to the controlled area boundaries. Only objects found to be free of radioactive contamination are allowed to leave the controlled area. Additionally, for radiation protection equipment such as gloves and shoe covers, as well as components and accessories removed or replaced from equipment within the controlled area, timely cleaning and de-contamination can be achieved if the tests show no radioactive contamination, effectively reducing the storage and disposal costs of radioactive waste. These applications require radioactive contamination detectors to be fast, have low detection limits, and high sensitivity.

[0003] Currently, the main measuring devices used for detecting radioactive contamination in small objects include HI-Q's SIM series and CANBERRA's Cronos series. The main drawbacks of these devices are:

[0004] 1) Currently available small object radioactive contamination detectors do not have alpha contamination detection capabilities; they can only perform gamma or gamma / beta detection. In some buildings of nuclear facilities and radiation control areas for radioactive isotope production, alpha surface contamination is a significant source of radioactive contamination from small objects, and traditional small object contamination detectors cannot meet the requirements of such application scenarios.

[0005] 2) Existing small object measuring instruments mainly use two large-area plastic scintillators arranged on both sides of the measuring device or four plastic scintillators arranged on the four sides of the detector, which cannot achieve a fully enclosed 4π measurement without dead zones and have low measurement sensitivity.

[0006] 3) Current small object measuring instruments do not take into account the influence of the background radioactivity of the small object itself. When the background radioactivity of the small object is high, the measurement error is large.

[0007] 4) Current small object radioactive contamination measuring instruments have a detection limit of 50-100 Bq (measurement time 15s). For lighter objects, the activity concentration may exceed the clean release limit specified by national standards. Summary of the Invention

[0008] In view of this, in order to overcome the shortcomings of the prior art, the object of the present invention is to provide an improved measuring device for identifying radioactive contamination.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A measuring device for identifying radioactive contamination includes an upper detector group, a lower detector group, a left detector group, a right detector group, a front detector group, and a rear detector group. The upper detector group, lower detector group, left detector group, right detector group, front detector group, and rear detector group constitute a fully enclosed 4π measuring chamber for measurement. Each detector group includes one or more detectors. Each detector includes a plastic scintillator and a photomultiplier tube. The detection surface of the plastic scintillator on the detector in the lower detector group is covered with a zinc sulfide coating.

[0011] The present invention provides a measuring device for identifying radioactive contamination, employing background optimization technology and a counting judgment limit method to rapidly and sensitively identify whether small objects are radioactively contaminated. The measuring device can measure X-rays, gamma rays, beta rays, and alpha rays. In some embodiments, a mesh tray is provided at the bottom of the chamber to support the small object to be measured. A zinc sulfide coating enables alpha contamination measurement, and the mesh structure of the object tray allows alpha rays to pass through it. An alpha ray detector is mounted at the bottom, ensuring that small objects of different sizes can approach the alpha detector, preventing alpha rays from being undetectable due to air absorption.

[0012] According to some preferred embodiments of the present invention, the small object to be measured refers to an object brought into the radiation control area by radiation workers and to be taken out of the radiation control area after the work is completed. This includes tools, instruments, toolboxes, keys, notebooks, and radiation protection equipment such as safety helmets, gloves, and dose alarms. In addition, it also includes equipment parts that are to be cleaned and decontrolled after the equipment in the control area has been removed or replaced.

[0013] According to some preferred embodiments of the present invention, the upper and lower detector groups are of the same size; the left and right detector groups are of the same size; and the front and rear detector groups are of the same size. Using identical structural dimensions facilitates detector fabrication, installation, replacement, and maintenance.

[0014] According to some preferred embodiments of the present invention, the upper detector group, lower detector group, left detector group, and right detector group each include two upper detectors, two lower detectors, two left detectors, and two right detectors, and the front detector group and rear detector group each include one front detector and one rear detector.

[0015] According to some preferred embodiments of the present invention, the upper detector sequentially comprises a plastic scintillator, a tapered light guide, and a photomultiplier tube; the photomultiplier tube is mounted on the back side of the plastic scintillator and perpendicular to the plastic scintillator, and the tapered light guide is used to connect the plastic scintillator and the photomultiplier tube.

[0016] According to some preferred embodiments of the present invention, the lower detector sequentially comprises a zinc sulfide coating, a plastic scintillator, a tapered light guide, and a photomultiplier tube; the zinc sulfide coating covers the detection surface of the plastic scintillator, the photomultiplier tube is mounted on the back side of the plastic scintillator and perpendicular to the plastic scintillator, and the tapered light guide connects the plastic scintillator and the photomultiplier tube. The tapered light guide allows the scintillating light from the plastic scintillator to be focused onto the photomultiplier tube.

[0017] According to some preferred embodiments of the present invention, the front detector, rear detector, left detector, and right detector each include a plastic scintillator, a fixing member, and a photomultiplier tube. The photomultiplier tube is fixed to the plastic scintillator by the fixing member, and the fixing member and the photomultiplier tube are provided at both ends of the plastic scintillator along its length. The fixing member has the same dimensions as the cross-sectional dimensions of the plastic scintillator and is fixed to the plastic scintillator by screws.

[0018] According to some preferred embodiments of the present invention, the scintillator signals of the left detector group, right detector group, front detector group and rear detector group are output by dual photomultiplier tubes; the signals of the upper detector and lower detector are output by anti-coincidence.

[0019] Specifically, among the front detector, rear detector, left detector, and right detector, when the photomultiplier tubes at both ends of a plastic scintillator simultaneously produce signals within a given time interval, the output is a valid signal; when only one end of the photomultiplier tube outputs a signal, it is an invalid signal.

[0020] The difference between the total output signal count of the upper and lower detectors and the coincidence signal count of the upper and lower detectors is the valid output signal count; the total output signal count is the sum of the output signal counts of the two upper detectors and the two lower detectors; the coincidence signal count is the sum of the coincidence signal counts of any one of the upper detectors and any one of the lower detectors.

[0021] According to some preferred embodiments of the invention, a fully enclosed 4π measurement chamber is formed by detectors on the front, rear, left, and right sides, as well as the top and bottom. The photomultiplier tubes of the front, rear, left, and right detectors are arranged at the top and bottom ends of the plastic scintillator. The photomultiplier tube of the upper detector is located on the back of the plastic scintillator and faces upwards, while the photomultiplier tube of the lower detector is located on the back of the plastic scintillator and faces downwards. That is, all the plastic scintillator photomultiplier tubes are arranged in either upward or downward directions. The overlap thickness at the junctions of the detectors is the same as the thickness of the scintillator detector, ensuring that the measurement chamber provides 4π measurement without blind spots.

[0022] The present invention also provides a method for measuring radioactive contamination using the above-described measuring device, comprising the following steps:

[0023] The measuring device measures the item to be tested, and the net count obtained is compared with the judgment limit. If the net count is higher than the judgment limit, it is judged as contaminated; if the net count is lower than the judgment limit, it is judged as uncontaminated.

[0024] According to some preferred embodiments of the present invention, the net count is calculated according to formulas 1-3:

[0025] N n =N s -N b …………………………………………(1)

[0026] N s =N U1 +N U2 +N L1 +N L2 +N R1 +N R2 +N F +N B +N D1 +N D2 ………………(2)

[0027]

[0028] The judgment limit is calculated according to Formula 4:

[0029]

[0030] In the formula, N n For the net count, N s For the total count, N b For background counting, N U1 N U2 The total counts for the two upper detectors are N. L1 N L2 N R1 NR2 N F N B These are the coincidence signal counts for the left, right, front, and rear detectors, respectively; N D1 N D2 These represent the total counts of the two lower detectors; N U1b N U2b These are the total background counts of the two upper detectors, N. L1b N L2b N R1b N R2b N Fb N Bb These are the background coincidence signal counts for the left, right, front, and rear detectors, respectively; N D1b N D2b These represent the total background counts of the two lower detectors; N U1-D1 N U1-D2 N U2-D1 N U2-D2 These are the coincidence signal outputs from the upper and lower detectors, respectively, N. sb L represents the baseline measurement or database baseline value of the small object before it enters the control area. C For judgment limits.

[0031] According to some preferred embodiments of the present invention, the background includes a cavity background of the measuring device, a small object measurement background, and a small object background database; the cavity background of the measuring device is the counting of the measuring device when there are no small objects in the measuring chamber, which is usually measured periodically or when the measuring device is idle; the small object measurement background refers to the counting of small objects when they enter the control area and are measured by the measuring device, and this method is mainly for small objects with potentially high background radioactivity; the small object background database refers to the background measurement of commonly used small objects such as safety helmets, tools, toolboxes, canvas bags, etc., and the formation of the background data into a database, which is used as a general background for small objects of the same category.

[0032] Furthermore, by using the aforementioned small object baseline database, it is possible to avoid performing separate baseline measurements on each object, thereby enabling rapid measurement of small objects.

[0033] Due to the adoption of the above technical solutions, the advantages of this invention compared to existing technologies are as follows: The radioactive contamination identification measuring device of this invention uses a scintillator detector with a six-sided staggered arrangement, achieving 4π measurement without dead zones and improving the sensitivity of the measuring device; the photomultiplier tubes of the detector are arranged in two directions, reducing the size of the equipment; the lower detector is coated with zinc sulfide, solving the defect that traditional contamination measuring equipment cannot simultaneously measure α, β, and γ; the scintillator signal uses a double-ended photomultiplier tube coincidence output, reducing electronic noise interference from the detector; the anti-coincidence output of the upper and lower detectors subtracts part of the cosmic ray response; combined with background optimization technology, ultra-low background measurement of the detector is achieved, solving the problem of high detection limits of traditional equipment. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a three-dimensional structural diagram of the measuring device in a preferred embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the structure of the front or rear detector of the measuring device in a preferred embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of the structure of the left or right detector of the measuring device in a preferred embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the upper detector of the measuring device in a preferred embodiment of the present invention;

[0039] Figure 5 This is a schematic diagram of the structure of the lower detector of the measuring device in a preferred embodiment of the present invention;

[0040] Figure 6 This is a flowchart illustrating the measurement method in a preferred embodiment of the present invention;

[0041] In the attached diagram: 1. Front detector; 2. Left detector; 3. Upper detector; 4. Rear detector; 5. Right detector; 6. Lower detector; 7. Tray; 11. Front (rear) detector photomultiplier tube; 12. Fixing component for the front (rear) detector photomultiplier tube; 13. Fixing screw for the fixing component; 14. Front (rear) detector plastic scintillator; 21. Left (right) detector photomultiplier tube; 22. Fixing component for the left (right) detector photomultiplier tube; 23. Fixing screw for the fixing component; 24. Left (right) detector plastic scintillator; 31. Upper detector photomultiplier tube; 32. Upper detector tapered light guide; 33. Upper detector plastic scintillator; 61. Lower detector zinc sulfide coating; 62. Lower detector plastic scintillator; 63. Lower detector tapered light guide; 64. Lower detector photomultiplier tube. Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0043] Example 1 Detection Device

[0044] like Figure 1-5 As shown, the high-sensitivity detection device for identifying radioactive contamination in small objects in this embodiment includes an upper detector group, a lower detector group, a left detector group, a right detector group, a front detector group, a rear detector group, and an object tray 7. The upper, lower, left, right, front, and rear detector groups constitute a fully enclosed 4π measurement chamber for measurement. The object tray 7 is located at the bottom of the measurement chamber and is used to support the object to be measured. Each detector group includes one or more detectors, and each detector includes a plastic scintillator and a photomultiplier tube. The detection surface of the plastic scintillator on the detector in the lower detector group is covered with a zinc sulfide coating. The upper and lower detector groups are the same size; the left and right detector groups are the same size; and the front and rear detector groups are the same size. Using identical structural dimensions facilitates detector fabrication, installation, replacement, and maintenance. Preferably, the dimensions of the front detector group and the rear detector group are 60cm (length) × 40cm (width) × 5cm (thickness); the dimensions of the left detector group and the right detector group are 60cm (length) × 30cm (width) × 5cm (thickness); and the dimensions of the upper detector group and the lower detector group are 30cm (length) × 30cm (width) × 5cm (thickness).

[0045] Specifically, the upper detector group, lower detector group, left detector group, and right detector group each include two upper detectors, two lower detectors, two left detectors, and two right detectors, and the front detector group and rear detector group each include one front detector and one rear detector.

[0046] like Figure 2 As shown, both the front detector 1 and the rear detector 4 include a front (rear) detector photomultiplier tube 11, a front (rear) detector photomultiplier tube fixing component 12, a fixing screw 13, and a front (rear) large-area plastic scintillator 14. The front detector 1 and the rear detector 4 are the same size and shape. The front detector 1 is rotatably mounted on the device door for opening and closing. Both the front detector 1 and the rear detector 4 use double-ended photomultiplier tubes to output signals. The photomultiplier tube 11 is installed at the upper and lower ends along the length of the plastic scintillator 14.

[0047] like Figure 3 As shown, each left detector 2 and right detector 5 includes a left (right) detector photomultiplier tube 21, a left (right) detector photomultiplier tube fixing component 22, a fixing screw 23, and a left (right) large-area plastic scintillator 24. Both left detector 2 and right detector 5 use dual-ended photomultiplier tubes to output signals, with the photomultiplier tube 11 installed at the upper and lower ends along the length of the plastic scintillator 24.

[0048] like Figure 4 As shown, each upper detector 3 includes an upper detector photomultiplier tube 31, an upper detector tapered light guide 32, and an upper detector plastic scintillator 33. Two upper detectors are installed inside the side detectors, with the detectors overlapping in the same dimension as the scintillator thickness (i.e., 5 cm). Specifically, the top surface of the plastic scintillator 33 in the upper detector is flush with the top surfaces of the plastic scintillators in the front, rear, left, and right detectors. To output the upper detector signal, the photomultiplier tube 31 is vertically mounted on the back of the scintillator 33 and connected via the tapered light guide 32. The tapered light guide 32 allows the scintillator light to be focused onto the photomultiplier tube.

[0049] like Figure 5 As shown, each lower detector 6 includes a lower detector zinc sulfide scintillator coating 61, a large-area plastic scintillator 62, a lower detector conical light guide 63, and a lower detector photomultiplier tube 64. The dimensions and installation method of the lower detector are the same as those of the upper detector 3. Furthermore, the zinc sulfide coating of the lower detector enables the measurement of surface contamination on small objects (α-rays). The lower detector 6, equipped with α-ray measurement capabilities, is installed at the bottom of the measuring device, ensuring that small objects of different sizes can be brought close to the detector, thus improving the device's sensitivity to α-rays.

[0050] The object tray 7, which supports the measurement of small objects, is designed with a mesh structure to ensure that alpha and beta rays, which have weaker penetrating power, can pass through the support plate and reach the detector surface. Preferably, the distance between the object tray 7 and the surface of the lower detector is no more than 1 cm.

[0051] Preferably, a radiation shield is installed outside the detector, which can typically be made of lead with a thickness of 2.5 cm or 5 cm, and a copper shielding layer with a thickness of 0.2 to 0.5 cm is added inside the lead chamber to further shield the characteristic X-rays of lead.

[0052] In this embodiment, the fully enclosed 4π measurement chamber of the measuring device is enclosed by detectors on the front, rear, left, and right sides, as well as the top and bottom. The photomultiplier tubes of the front, rear, left, and right detectors are arranged at the top and bottom ends of the plastic scintillator. The photomultiplier tube of the upper detector is located on the back of the plastic scintillator and faces upwards, while the photomultiplier tube of the lower detector is located on the back of the plastic scintillator and faces downwards. That is, all the photomultiplier tubes of the plastic scintillator are arranged in both upward and downward directions. The overlap thickness at the junctions of the detectors is the same as the thickness of the scintillator detector, ensuring that the measurement chamber provides 4π measurement without blind spots.

[0053] The scintillator signals of the left, right, front, and rear detector groups use dual photomultiplier tubes for coincidence output; the signals of the upper and lower detectors use anti-coincidence output. Specifically, in the front, rear, left, and right detectors, when the photomultiplier tubes at both ends of a plastic scintillator simultaneously produce signals within a given time interval, the output is a valid signal; when only one of the photomultiplier tubes outputs a signal, it is an invalid signal. The difference between the total output signal count of the upper and lower detectors and the coincidence signal count of the upper and lower detectors is the valid output signal count; the total output signal count is the sum of the output signal counts of the two upper detectors and the two lower detectors; the coincidence signal count is the sum of the coincidence signal counts of any one upper detector and any one lower detector.

[0054] Small objects to be measured refer to objects brought into the radiation control area by radiation workers and to be taken out of the radiation control area after the work is completed. These include tools, instruments, toolboxes, keys, notebooks, and radiation protection equipment such as safety helmets, gloves, and dose alarms. In addition, they also include equipment parts that have been removed or replaced within the control area and are intended to be cleaned and decontrolled.

[0055] Example 2 Measurement Method

[0056] like Figure 5 As shown, the method for measuring radioactive contamination using the aforementioned measuring device in this embodiment includes detection of small objects before they enter the controlled area and detection of them being taken out of the controlled area, as detailed below:

[0057] Entering the controlled area: 1) Before carrying small objects into the controlled area, staff should perform a rapid baseline measurement using the measuring device in Example 1, typically for 5 seconds; 2) If the measured value is abnormal, i.e., if the measured value differs significantly from the value in the baseline database of similar objects, the measurement time should be extended (usually 1 minute), and the identification of the small object and the corresponding baseline value should be recorded in the measuring device; 3) If the measured value is normal, i.e., if the measured value is at the same level as the value in the baseline database of similar objects, the measurement should end.

[0058] Remove from the control area: 1) Place the small object to be removed from the control area into the measuring device in Example 1 for measurement, typically for 15 seconds; 2) Use the background value of the object. If the background value of the object is recorded in the device, use the measured background value; otherwise, use the background value from the database of similar small objects; 3) Calculate the net count and judgment limit of the small object based on the measured value and the background value; 4) Compare the net count and judgment limit. If the net count is higher than the judgment limit, it is determined that the object is radioactively contaminated and should be further tested or decontaminated before measurement. If the net count is lower than the judgment limit, it is determined that the object is not contaminated or the component can be cleaned and released from control.

[0059] The net count is calculated according to formula 1-3:

[0060] N n =N s -N b …………………………………………(1)

[0061] N s =N U1 +N U2 +N L1 +N L2 +N R1 +N R2 +N F +N B +N D1 +N D2 ………………(2)

[0062]

[0063] The judgment limit is calculated based on Formula 4:

[0064]

[0065] In the formula, N n For the net count, N s For the total count, N b For background counting, N U1 N U2 The total counts for the two upper detectors are N.L1 N L2 N R1 N R2 N F N B These are the coincidence signal counts for the left, right, front, and rear detectors, respectively; N D1 N D2 These represent the total counts of the two lower detectors; N U1b N U2b These are the total background counts of the two upper detectors, N. L1b N L2b N R1b N R2b N Fb N Bb These are the background coincidence signal counts for the left, right, front, and rear detectors, respectively; N D1b N D2b These represent the total background counts of the two lower detectors; N U1-D1 N U1-D2 N U2-D1 N U2-D2 These are the coincidence signal outputs from the upper and lower detectors, respectively, N. sb L represents the baseline measurement or database baseline value of the small object before it enters the control area. C For judgment limits.

[0066] Background includes the cavity background of the measuring device, the small object measurement background, and the small object background database. The cavity background of the measuring device is the count of the measuring device when there are no small objects in the measuring chamber, which is usually measured periodically or when the measuring device is idle; the small object measurement background refers to the count of small objects measured when they enter the control area using the measuring device, and this method is mainly for small objects that may have high background radioactivity; the small object background database refers to the background measurements of commonly used small objects such as safety helmets, tools, toolboxes, and canvas bags, and the background data is compiled into a database, which is used as a general background for small objects of the same category.

[0067] By using a baseline database of small objects, it is possible to avoid performing separate baseline measurements on each object, enabling rapid measurement of small objects.

[0068] This invention relates to a highly sensitive measuring device for identifying radioactive contamination in small objects. The device comprises a fully enclosed 4π measuring chamber consisting of two upper detectors, two left detectors, two right detectors, one front detector, one rear detector, and two lower detectors. A mesh tray for small objects is installed at the bottom of the measuring chamber. Background optimization technology and a counting judgment limit method are used to quickly and sensitively identify whether small objects are radioactively contaminated. The device can measure X-rays, including gamma rays, beta rays, and alpha rays. The left and right detectors have the same structural dimensions, as do the front and rear detectors; the upper and lower detectors have the same dimensions, and the plastic scintillator detection surface of the lower detector is covered with a zinc sulfide coating. The scintillator signals from the left, right, front, and rear detectors are all output via dual photomultiplier tubes; the signals from the upper and lower detectors are output via anti-coincidence. The radioactive contamination identification measuring device and method of this invention are also applicable to the cleaning and control measurement of small objects. The measuring device adopts a scintillator detector with six sides staggered, realizing 4π measurement without dead zones and improving the sensitivity of the detector. The photomultiplier tubes of the detector are arranged at the top and bottom ends, reducing the size of the equipment. The bottom detector is coated with zinc sulfide, which solves the defect of traditional contamination measuring equipment that cannot measure α, β and γ simultaneously. The scintillator signal adopts the coincidence output of the double-ended photomultiplier tube, which reduces the electronic noise interference of the detector. The anti-coincidence output of the top and bottom detectors is used to subtract part of the cosmic ray response. Combined with the background optimization technology, the detector achieves ultra-low background measurement and solves the problem of high detection limit of traditional equipment.

[0069] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A measuring device for identifying radioactive contamination, characterized in that, The system includes an upper detector group, a lower detector group, a left detector group, a right detector group, a front detector group, and a rear detector group. These groups form a measurement chamber. Each detector group includes one or more detectors, and each detector includes a plastic scintillator and a photomultiplier tube. The plastic scintillator detection surface of the detector in the lower detector group is covered with a zinc sulfide coating. The scintillator signals from the left, right, front, and rear detector groups are output using dual photomultiplier tubes for coincidence. The signals from the upper and lower detectors are output using anti-coincidence. The upper detector group, lower detector group, left detector group, and right detector group each include two upper detectors, two lower detectors, two left detectors, and two right detectors, and the front detector group and rear detector group each include one front detector and one rear detector; The upper detector comprises, in sequence, a plastic scintillator, a tapered light guide, and a photomultiplier tube; the photomultiplier tube is mounted on the back of the plastic scintillator and perpendicular to the plastic scintillator, and the tapered light guide is used to connect the plastic scintillator and the photomultiplier tube; The lower detector sequentially comprises a zinc sulfide coating, a plastic scintillator, a tapered light guide, and a photomultiplier tube; the zinc sulfide coating covers the detection surface of the plastic scintillator, the photomultiplier tube is mounted on the back side of the plastic scintillator and perpendicular to it, and the tapered light guide connects the plastic scintillator and the photomultiplier tube; The front detector, rear detector, left detector, and right detector each include a plastic scintillator, a fixing element, and a photomultiplier tube. The photomultiplier tube is fixed to the plastic scintillator by the fixing element. The fixing element and the photomultiplier tube are provided at both ends of the plastic scintillator along its length. Among the front detector, rear detector, left detector, and right detector, when the photomultiplier tubes at both ends of a plastic scintillator simultaneously produce signals within a given time interval, the output is a valid signal. When only one end of the photomultiplier tube outputs a signal, it is an invalid signal. The difference between the total output signal count of the upper and lower detectors and the coincidence signal count of the upper and lower detectors is the valid output signal count; the total output signal count is the sum of the output signal counts of the two upper detectors and the two lower detectors; the coincidence signal count is the sum of the coincidence signal counts of any one of the upper detectors and any one of the lower detectors.

2. The measuring device according to claim 1, characterized in that, The upper and lower detector groups are the same size; the left and right detector groups are the same size; and the front and rear detector groups are the same size.

3. A method for measuring radioactive contamination using the measuring device according to any one of claims 1-2, characterized in that, Includes the following steps: The measuring device measures the item to be tested, and the net count obtained is compared with the judgment limit. If the net count is higher than the judgment limit, it is judged as contaminated; if the net count is lower than the judgment limit, it is judged as uncontaminated.

4. The measurement method according to claim 3, characterized in that, The net count is calculated according to formulas 1-3: …………………………………………（1）； ………………（2）； ………（3）； The judgment limit is calculated according to Formula 4: ………………………………………（4）； In the formula, Net count, For the total count, For background counting, , These are the total counts for the two upper detectors. , , , , , These are the coincidence signal counts for the left, right, front, and rear detectors, respectively. , These are the total counts for the two lower detectors; , These are the total background counts of the two upper detectors, , , , , , These are the background coincidence signal counts for the left, right, front, and rear detectors, respectively. , These are the total background counts of the two lower detectors, respectively; , , , These are the coincidence signal outputs from the upper and lower detectors, respectively. These are baseline measurements or database baseline values ​​for small objects before they enter the controlled area. For judgment limits.

Images