Automatic photonic scanning collimator for germanium crystal dead layer thickness and measuring method

Abstract

The application discloses a kind of germanium crystal dead layer thickness automation photon scanning collimator and measuring method, wherein the germanium crystal dead layer thickness automation photon scanning collimator includes the plexiglass plate being set in the top of lead chamber and being rotatable relative to lead chamber, the pose adjustable measuring component is arranged on the plexiglass plate, the upper surface of lead chamber is provided with the openable and closable lead cover for covering the plexiglass plate and pose adjustable measuring component.The application can realize the measurement of high-purity germanium crystal dead layer thickness, solve the problem that dead layer related parameters cannot be measured.The whole device is easy to process and install, and can realize measurement in multiple directions;The method creatively uses photon scanning method, which can further reduce cost, and the accurate measurement of dead layer can be realized without disassembling the detector to expose high-purity germanium crystal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radionuclide analysis, and particularly relates to a germanium crystal dead layer thickness automatic photon scanning collimator and a measuring method. BACKGROUND

[0002] A high purity germanium gamma spectrometer can realize high-accuracy quantitative and qualitative analysis of gamma radionuclides, wherein the detection efficiency is the basis for realizing quantitative analysis, and depends on the volume of the high purity germanium crystal. When the high purity germanium gamma spectrometer is produced, the outer layer of the high purity germanium crystal is a dead layer of germanium material, that is, the layer of material cannot collect particles. The dead layer thickness is only roughly measured during production, and the dead layer thickness at each position is not uniform, but when the product is shipped, the manufacturer will only give a rough dead layer thickness value. Since the dead layer thickness of the high purity germanium gamma spectrometer changes during use, the change in the dead layer thickness will directly affect the detection efficiency, thereby affecting the accurate quantitative analysis of gamma radionuclides. Therefore, accurate measurement of the dead layer thickness and uniformity of the high purity germanium crystal is of great significance to ensure accurate quantitative analysis of gamma radionuclides.

[0003] At present, when the high purity germanium gamma spectrometer is shipped, an industrial CT with a large tube voltage is used to scan the detector crystal, obtain a CT image thereof, and obtain the accurate size of each part of the detector crystal. However, the dead layer and the high purity germanium crystal are both Ge materials, and therefore the dead layer and the high purity germanium crystal cannot be distinguished on the CT image, so this method cannot measure the dead layer thickness. Therefore, there is an urgent need for a device and method for accurately measuring the dead layer thickness of the high purity germanium crystal. SUMMARY

[0004] In view of the above problems in the prior art, the present application aims to provide a germanium crystal dead layer thickness automatic photon scanning collimator and a measuring method, so as to realize accurate measurement of the dead layer thickness of the high purity germanium crystal.

[0005] To achieve the above-mentioned application purposes, the technical scheme adopted by the present application is as follows:

[0006] On the one hand, a germanium crystal dead layer thickness automatic photon scanning collimator is provided, which comprises a lead chamber provided with a germanium crystal, the top of the lead chamber is provided with an organic glass plate which can rotate relative to the lead chamber, the organic glass plate is provided with a pose-adjustable measuring assembly, and the upper surface of the lead chamber is provided with a openable and closable lead cover for covering the organic glass plate and the pose-adjustable measuring assembly.

[0007] The pose-adjustable measurement assembly comprises a horizontal base, a sliding block and a vertical metal frame; the organic glass plate is provided with a groove through which the vertical metal frame passes; the lower end of the vertical metal frame is provided with an L-shaped rotatable support penetrating through the vertical metal frame; the end of the L-shaped rotatable support is provided with a photon generator; the top of the vertical metal frame is provided with a support table, and the support table is provided with a rotation angle adjuster; the rotation angle adjuster is provided with a transmission belt, and the other end of the transmission belt is located at the position where the L-shaped rotatable support penetrates out of the vertical metal frame, so that the rotation angle adjuster can drive the L-shaped rotatable support to rotate through the transmission belt, thereby adjusting the irradiation angle of the photon generator to the germanium crystal (6);

[0008] The horizontal base is arranged on the organic glass plate; the upper surface of the horizontal base is provided with a first sliding rail, and the front surface of the vertical metal frame is provided with a second sliding rail; the lower surface of the sliding block is matched with the first sliding rail and can slide left and right along the first sliding rail to realize left and right position adjustment of the photon generator; the back surface of the sliding block is matched with the second sliding rail and can slide up and down relative to the second sliding rail to realize up and down height adjustment of the photon generator.

[0009] Further, the rotation plane of the L-shaped rotatable support is perpendicular to the horizontal plane and parallel to the plane where the vertical metal frame is located.

[0010] Further, the horizontal base and the vertical metal frame are both provided with scales.

[0011] Further, the sliding block is provided with a first position adjuster and a second position adjuster; the first position adjuster is matched with the first sliding rail and is used for controlling the left and right movement of the sliding block; the second position adjuster is matched with the second sliding rail and is used for controlling the up and down movement of the vertical metal frame.

[0012] Further, the photon source of the photon generator is americium-241, and the front end of the photon source is provided with a collimator.

[0013] Further, the upper surface of the lead chamber is provided with a limiting table for limiting the shaking of the organic glass plate, and the organic glass plate is buckled on the limiting table; the upper surface of the lead chamber is also provided with an angle scale and a level.

[0014] On the other hand, a germanium crystal dead layer thickness measurement method based on a germanium crystal dead layer thickness automatic photon scanning collimator is provided, which comprises the following steps:

[0015] S1, the first measurement point is located at the center of the germanium crystal, the pose-adjustable measurement assembly is adjusted, the exit of the photon generator is 2 cm away from the upper surface of the germanium crystal, the photon incidence angle is 90°, and the corresponding peak area count (the peak area count can be obtained from the measurement software) is recorded;

[0016] S2, adjust the pose of the adjustable measurement assembly, so that the photon incident angle of the photon generator is 45°, and record the corresponding peak area count;

[0017] S3, rotate the organic glass plate, select a measurement point every 5 mm on the outer surface of the germanium crystal (along the diameter of the circle at the top of the crystal (the east to west and south to north diameter is specified, and the interval point is 5 mm)), repeat the measurement process of steps S1 and S2, and record the corresponding peak area count;

[0018] S4, adjust the pose of the adjustable measurement assembly, so that the exit port of the photon generator is located 3 cm below the surface of the germanium crystal, the photon is vertically incident on the germanium crystal, and the exit port of the photon generator is 2 cm away from the side surface of the germanium crystal, and record the corresponding peak area count;

[0019] S5, adjust the slider to move the photon generator towards the germanium crystal, and select a measurement point every 5 mm, and record the corresponding peak area count;

[0020] S6, rotate the organic glass plate, repeat step S5 every 90°, and record the corresponding peak area count;

[0021] S7, obtain the dead layer thickness of the germanium crystal according to the recorded peak area count.

[0022] Further, the dead layer thickness calculation expression of the germanium crystal is (all measurement points need 90° and 45° data, and the measurement formula is the same):

[0023]

[0024] Where d Ge is the dead layer thickness of the germanium crystal (6); ln is the natural logarithm; N 45 is the peak area count rate (peak area count divided by measurement time) in the direction of 45° photon incident angle, N 90 is the count rate in the direction of 90° photon incident angle; μ Al , μ Ge , μ Be are the linear attenuation coefficients of aluminum, germanium and beryllium, respectively, d Al , d Be are the thicknesses of aluminum and beryllium. The linear attenuation coefficients of aluminum, germanium and beryllium and the thicknesses of aluminum and beryllium are introduced here because the photon needs to pass through these materials before hitting the crystal. Changing the incident angle will change the thickness of the material through which the photon passes.

[0025] Further, the linear attenuation coefficients of aluminum, germanium and beryllium are obtained by four-order polynomial fitting, and the fitting expression is:

[0026] ln(μ)=a+bln(E)+cln(E)2 + dln(E) 3 + e ln(E) 4

[0027] Wherein E is the energy of different materials, the different materials include aluminum, germanium, beryllium, mu is the linear attenuation coefficient of different materials, a, b, c, d, e are all to be fitted constants.

[0028] Further, when recording the peak area count at the same position, the average of three measurements is measured as the peak area count corresponding to the position.

[0029] The beneficial effects of the present application are:

[0030] 1. The thickness of the dead layer of high-purity germanium crystal can be measured, and the problem that the related parameters of the dead layer cannot be measured is solved.

[0031] 2. The whole device is easy to process and install, and can realize measurement in multiple directions; the method creatively uses photon scanning method, which can further reduce the cost, and the accurate measurement of the dead layer can be realized without disassembling the detector to expose the high-purity germanium crystal. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a schematic diagram of the overall structure of the automatic photon scanning collimator.

[0033] Figure 2 It is a schematic diagram of the structure of the lead chamber of the detector.

[0034] Figure 3 It is a schematic diagram of the structure of the pose-adjustable measurement assembly.

[0035] Wherein: 1, lead chamber; 2, organic glass plate; 3, pose-adjustable measurement assembly; 4, openable and closable lead cover; 5, limiting table; 6, germanium crystal; 7, L-shaped rotatable support; 8, photon emitter; 9, vertical metal frame; 10, horizontal base; 11, first sliding rail; 12, first position adjuster; 13, second position adjuster; 14, sliding block; 15, second sliding rail; 16, supporting table; 17, transmission belt; 18, rotation angle adjuster.

[0036] Figure 4 It is a schematic diagram of the structure of the automatic photon scanning collimator in use.

[0037] Figure 5 It is a flowchart of the measurement method of the dead layer thickness of the germanium crystal.

[0038] Figure 6 It is a measurement principle diagram of the automatic photon scanning collimator.

[0039] Figure 7 It is a model diagram of the high-purity germanium crystal.

[0040] Figure 8 A curve graph for the dead layer of high-purity germanium crystal. DETAILED DESCRIPTION

[0041] The specific embodiments of the present application are described below to enable those skilled in the art to understand the present application, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, as long as various changes are within the spirit and scope of the present application defined and determined by the appended claims, all the applications utilizing the concept of the present application are within the scope of protection.

[0042] Example 1

[0043] Reference Figures 1-2 A lead chamber 1 provided with a germanium crystal 6, an organic glass plate 2 rotatable relative to the lead chamber 1 is arranged on the top of the lead chamber 1, a pose-adjustable measurement assembly 3 is arranged on the organic glass plate 2, a lead cover 4 capable of being opened and closed is arranged on the upper surface of the lead chamber 1 for covering the organic glass plate 2 and the pose-adjustable measurement assembly 3; a limiting table 5 for limiting the shaking of the organic glass plate 2 is arranged on the upper surface of the lead chamber 1, and the organic glass plate 2 is buckled on the limiting table 5; an angle scale and a level are further arranged on the upper surface of the lead chamber 1.

[0044] As a preferred mode, reference Figure 3 The pose-adjustable measurement assembly 3 includes a horizontal base 10, a sliding block 14 and a vertical metal frame 9; scales are arranged on the horizontal base 10 and the vertical metal frame 9. A slot is arranged on the organic glass plate 2 for the vertical metal frame 9 to pass through; an L-shaped rotatable support 7 penetrating the vertical metal frame 9 is arranged at the lower end of the vertical metal frame 9; the rotation plane of the L-shaped rotatable support 7 is perpendicular to the horizontal plane and parallel to the plane where the vertical metal frame 9 is located. A photon generator 8 is arranged at the end of the L-shaped rotatable support 7; the photon source of the photon generator 8 is americium-241, and a collimator is arranged at the front end of the photon source. A supporting table 16 is arranged at the top of the vertical metal frame 9, and a rotation angle adjuster 18 is arranged on the supporting table 16; a transmission belt 17 is arranged on the rotation angle adjuster 18, and the other end of the transmission belt 17 is located at the position where the L-shaped rotatable support 7 penetrates the vertical metal frame 9, so that the rotation angle adjuster 18 can drive the L-shaped rotatable support 7 to rotate through the transmission belt 17, thereby adjusting the irradiation angle of the photon generator 8 to the germanium crystal 6;

[0045] A horizontal base 10 is mounted on an plexiglass plate 2; a first slide rail 11 is mounted on the upper surface of the horizontal base 10, and a second slide rail 15 is mounted on the front of the vertical metal frame 9; the lower surface of the slider 14 matches the first slide rail 11 and can slide left and right along the first slide rail 11 to adjust the left and right position of the photon generator 8; the back of the slider 14 matches the second slide rail 15 and allows the vertical metal frame 9 to slide up and down relative to the second slide rail 15 to adjust the height of the photon generator 8.

[0046] As a preferred embodiment, the slider 14 is provided with a first position adjuster 12 and a second position adjuster 13; the first position adjuster 12 is matched with the first slide rail 11 and is used to control the left and right movement of the slider 14; the second position adjuster 13 is matched with the second slide rail 15 and is used to control the up and down movement of the vertical metal frame 9.

[0047] Example 2

[0048] Reference Figure 5 A method for measuring the dead layer thickness of a germanium crystal based on the automated photonic scanning collimator provided in Example 1, specifically includes the following steps:

[0049] Step 1: Design a dedicated photon scanning collimator for measuring the dead layer thickness of germanium crystals. This collimator must ensure no photon leakage outside its outer edge, and at a distance of 2cm from the exit port, 96% of the emitted photons must be concentrated within a diameter of 4mm. This design should achieve the following: a transparent PMMA plate can be mounted on the lead shield of the detector, movable at the top of the shield, allowing the collimated position to be observed from the top during measurement; axial and radial movement control is possible; the photon incident angle can be adjusted from 0-180°; the photon collimator can be removed at any time, with internal grooves to fix the radiation source; and the position can be moved during the measurement of the dead layer on the side of the high-purity germanium crystal.

[0050] Step 2: Using photon transport software, a detector model was built. The dead layer thickness was varied, and gamma photons of different energies were introduced to determine the impact of changes in dead layer thickness on gamma photons of different energies. The specific model and results are detailed below. Figures 7-8 Analysis revealed that changes in the dead layer thickness have a greater impact on the count rate of photons in the low-energy region. Changing the angle is equivalent to altering the thickness through which photons pass within the dead layer. Therefore, using low-energy photons (59.5 keV) better reflects the influence of the incident angle on the count rate. 241 Am served as the photon source for this event.

[0051] Step three: remove the photon collimation device from the main body, then remove the lead cover above the collimation device with a "Y" adjustable wrench, put the photon source into the chamber, and fix it with the lead cover to ensure that the photon source does not move during the measurement process, reducing the error introduced by the movement of the photon source;

[0052] Step four: reassemble the collimator into the main body, adjust the angle knob to adjust the incident angle of the photons, and use a level to ensure that the current photon incident angle is 90°; place the entire device on the top of the lead chamber of the detector, fix the position with the transparent organic glass plate, divide the organic glass plate into N-S and W-E directions respectively, adjust the radial position of the photon collimator and lock the position of the organic glass plate and the top of the lead chamber, and ensure that the first measurement point is located at the center of the detector crystal. At this time, record the relative positions of the two scale lines on the left and right of the photon collimator and the relative positions of the organic glass plate and the top of the lead chamber; adjust the axial rotator to control the relative height between the photon collimator and the detector, ensure that the exit port of the photon collimator is 2 cm above the surface of the detector crystal, rotate the fixing button to lock the measurement height, and record the scale line positions of the up and down adjustments.

[0053] Step five: measure at the center point and record the peak area count, a total of 3 times, each measurement time is 7200s. Adjust the angle knob so that the photon incident angle is 45°, repeat the measurement 3 times, and record the peak area count; along the N-S and W-E directions drawn on the surface of the detector crystal, record a point every 5 mm, and repeat the measurement process;

[0054] Step six: adjust the axial position of the photon collimator so that the exit port of the photon collimator is 3 cm below the surface of the detector, adjust the photon exit angle so that the photon can reach the side dead layer of the detector crystal vertically, and fix the axial position and angle position respectively; adjust the radial knob so that the distance from the exit port of the photon collimator to the side dead layer is 2 cm, start measuring, measure 3 times, take the average value, and adjust the axial position, record a point every 5 mm, repeat the measurement process, and select N, S, W and E four directions respectively, repeat the measurement process.

[0055] Step seven: use the XCOM database to obtain the mass attenuation coefficients of Al, Ge, Be and other materials at different energies, obtain a set of E (energy)-μ (mass attenuation coefficient) data for different materials, take the natural logarithm of the data, use a fourth order polynomial to fit, obtain the fitting curve and fitting parameters, and realize the fitting output of the mass attenuation coefficient at different energies.

[0056] Fitting formula:

[0057] ln(μ)=a+bln(E)+cln(E) 2+dln(E) 3 +eln(E) 4

[0058] After interpolation, the interpolation data is taken as an index, that is, the interpolation of target energy can be realized.

[0059] Step eight: the calculation of dead layer thickness, the count rate of 45° and 90° and the following formula are used for calculation:

[0060]

[0061] Wherein, N 45 Is the collimation count rate in the direction of 45°, N 90 Is the collimation count rate in the direction of 90°, μ Al , μ Ge , μ Be Linear attenuation coefficient of aluminum, germanium, beryllium respectively, d Al , d Be The thickness of aluminum, beryllium respectively, wherein d Ge The thickness of germanium detector dead layer;The formula can be extended to any angle.

[0062]

[0063] The natural logarithm of the above formula is taken:

[0064] Then the final calculation formula of dead layer thickness is:

[0065]

[0066] In summary, the application develops a kind of high-purity germanium crystal dead layer thickness automation photon scanning collimator, based on this innovation, a kind of high-purity germanium crystal dead layer thickness measurement method is proposed, the accurate measurement of dead layer thickness is realized.

[0067] For those skilled in the art, it is obvious that the present application is not limited to the details of the above exemplary embodiments, and the present application can be realized in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

[0068] Furthermore, it should be understood that although the specification is described in terms of embodiments, not every embodiment includes every feature described. The specification can include implicit combinations of explicitly mentioned features and / or explicit combinations of implicitely mentioned features. Each embodiment depends on the explicit combinations of features and / or the implicit combinations of features made specifically within that embodiment, and each such embodiment can be combined with every other such embodiment to create further embodiments.

Claims

1. An automated photonic scanning collimator for germanium crystal dead layer thickness, characterized in that, Includes an plexiglass plate (2) that is set on the top of the lead chamber (1) and can rotate relative to the lead chamber (1), an adjustable position measurement component (3) is provided on the plexiglass plate (2), and an openable lead cover (4) is provided on the upper surface of the lead chamber (1) for covering the plexiglass plate (2) and the adjustable position measurement component (3). The pose-adjustable measurement component (3) includes a horizontal base (10), a slider (14), and a vertical metal frame (9); a groove is provided on the plexiglass plate (2) for the vertical metal frame (9) to pass through; an L-shaped rotatable bracket (7) is provided at the lower end of the vertical metal frame (9); a photon generator (8) is provided at the end of the L-shaped rotatable bracket (7); a support platform (16) is provided at the top of the vertical metal frame (9), and a rotation angle adjuster (18) is provided on the support platform (16); a transmission belt (17) is provided on the rotation angle adjuster (18), and the other end of the transmission belt (17) is located at the part where the L-shaped rotatable bracket (7) passes through the vertical metal frame (9), so that the rotation angle adjuster (18) can drive the L-shaped rotatable bracket (7) to rotate through the transmission belt (17), thereby adjusting the irradiation angle of the photon generator (8) on the germanium crystal (6) in the lead chamber (1); A horizontal base (10) is set on an plexiglass plate (2); a first slide rail (11) is provided on the upper surface of the horizontal base (10), and a second slide rail (15) is provided on the front of the vertical metal frame (9); the lower surface of the slider (14) matches the first slide rail (11) and can slide left and right along the first slide rail (11) to adjust the left and right position of the photon generator (8); the back of the slider (14) matches the second slide rail (15) and allows the vertical metal frame (9) to slide up and down relative to the second slide rail (15) to adjust the height of the photon generator (8).

2. The automated photonic scanning collimator for germanium crystal dead layer thickness according to claim 1, characterized in that, The rotation plane of the L-shaped rotatable bracket (7) is perpendicular to the horizontal plane and parallel to the plane of the vertical metal frame (9).

3. The automated photonic scanning collimator for germanium crystal dead layer thickness according to claim 1, characterized in that, Both the horizontal base (10) and the vertical metal frame (9) are equipped with scales.

4. The automated photonic scanning collimator for germanium crystal dead layer thickness according to claim 1, characterized in that, The slider (14) is provided with a first position adjuster (12) and a second position adjuster (13); the first position adjuster (12) is matched with the first slide rail (11) and is used to control the left and right movement of the slider (14); the second position adjuster (13) is matched with the second slide rail (15) and is used to control the up and down movement of the vertical metal frame (9).

5. The automated photonic scanning collimator for germanium crystal dead layer thickness according to claim 1, characterized in that, The photon source of the photon generator (8) is an Americium-241, and a collimator is provided at the front end of the photon source.

6. The automated photonic scanning collimator for germanium crystal dead layer thickness according to claim 1, characterized in that, The upper surface of the lead chamber (1) is provided with a limiting platform (5) for limiting the swaying of the plexiglass plate (2), and the plexiglass plate (2) is fastened on the limiting platform (5); the upper surface of the lead chamber (1) is also provided with an angle scale and a level.

7. A method for measuring the dead layer thickness of a germanium crystal based on an automated photonic scanning collimator according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Select the first measurement point located in the center of the germanium crystal (6), adjust the position adjustable measurement component (3) so that the distance from the outlet of the photon generator (8) to the upper surface of the germanium crystal (6) is 2cm and the photon incident angle is 90°, and record the corresponding peak area count. S2. Adjust the pose-adjustable measurement component (3) so that the photon incident angle of the photon generator (8) is 45° and record the corresponding peak area count. S3. Rotate the organic glass plate (2), select a measurement point every 5 mm along the defined NS and WE directions on the outer surface of the germanium crystal (6), repeat the measurement process of steps S1 and S2, and record the corresponding peak area count. S4. Adjust the pose-adjustable measurement component (3) so that the outlet of the photon generator (8) is located 3cm below the surface of the germanium crystal (6), the photon is perpendicularly directed towards the germanium crystal (6), and the outlet of the photon generator (8) is 2cm away from the side of the germanium crystal (6). Record the corresponding peak area count. S5. Adjust the slider (14) to move the photon generator (8) toward the germanium crystal (6), and select a measurement point every 5 mm of movement, and record the corresponding peak area count. S6. Rotate the plexiglass plate (2) and repeat step S5 once for every 90° rotation, and record the corresponding peak area count. S7. Obtain the dead layer thickness of germanium crystal (6) based on the recorded peak area count.

8. The method for measuring the dead layer thickness of a germanium crystal according to claim 7, characterized in that, The expression for calculating the dead layer thickness of germanium crystal (6) is as follows: Where d Ge The dead layer thickness of the germanium crystal (6) is ln; ln is the natural logarithm; N 45 It is the peak area counting rate along the direction with a photon incident angle of 45°, N 90 It is the count rate in the direction where the photon incident angle is 90°; μ Al μ Ge μ Be These are the linear decay coefficients of aluminum, germanium, and beryllium, respectively, and d Al d Be These are the thicknesses of aluminum and beryllium, respectively.

9. The method for measuring the dead layer thickness of a germanium crystal according to claim 8, characterized in that, The linear decay coefficients of aluminum, germanium, and beryllium were obtained by fitting a fourth-order polynomial, and the fitting expression is as follows: ln(µ)a+bln(E)+cln(E) 2 +dln(E) 3 +eln(E) 4 Where E represents the energy of different materials, including aluminum, germanium, and beryllium; μ represents the linear decay coefficient of different materials; and a, b, c, d, and e are constants to be fitted.

10. The method for measuring the dead layer thickness of a germanium crystal according to claim 7, characterized in that, When recording the peak area count at the same location, each measurement is taken three times and the average value is taken as the peak area count corresponding to that location.

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