Germanium crystal dead layer thickness automatic photon scanning collimator and measurement method

Abstract

The invention discloses a germanium crystal dead layer thickness automatic photon scanning collimator and a measurement method, the germanium crystal dead layer thickness automatic photon scanning collimator comprises an organic glass plate which is arranged on the top of a lead chamber and can rotate relative to the lead chamber, and the organic glass plate is provided with a pose adjustable measurement assembly. The upper surface of the lead chamber is provided with an openable and closable lead cover used for covering the organic glass plate and the pose-adjustable measuring assembly. The thickness of the dead layer of the high-purity germanium crystal can be measured, and the problem that relevant parameters of the dead layer cannot be measured is solved. The whole device is convenient to process and install, and can realize measurement in multiple directions; according to the method, a photon scanning method is creatively adopted, so that the cost can be further reduced, and accurate measurement of the dead layer can be realized without disassembling the detector to expose the high-purity germanium crystal.

Description

Technical Field

[0001] The present invention relates to the technical field of radionuclide analysis, and in particular to an automatic photon scanning collimator for the thickness of a germanium crystal dead layer and a measurement method thereof. Background Art

[0002] High-purity germanium gamma spectrometers enable highly accurate quantitative and qualitative analysis of gamma-radioactive nuclides. Detection efficiency, fundamental to achieving this quantitative analysis, depends on the volume of the high-purity germanium crystal. During the production of high-purity germanium gamma spectrometers, the outer layer of the high-purity germanium crystal is a dead layer of germanium material, meaning that this layer does not collect particles. The thickness of this dead layer is only roughly measured during production, and it is not uniform at every location. Upon shipment, the manufacturer only provides a rough dead layer thickness value. Since this dead layer thickness varies during use, variations in the dead layer directly affect detection efficiency and, consequently, the accurate quantitative analysis of gamma-radioactive nuclides. Therefore, accurate measurement of the dead layer thickness and uniformity of high-purity germanium crystals is crucial for ensuring accurate quantitative analysis of gamma-radioactive nuclides.

[0003] Currently, when high-purity germanium gamma spectrometers leave the factory, they use a high-voltage industrial CT scan to obtain a CT image of the detector crystal, which accurately measures the dimensions of each component. However, since both the dead layer and the high-purity germanium crystal are made of Ge, the two cannot be distinguished on the CT image, making this method incapable of measuring the dead layer thickness. Therefore, a device and method for accurately measuring the dead layer thickness of high-purity germanium crystals is urgently needed. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide an automated photon scanning collimator and a measurement method for the dead layer thickness of germanium crystals, so as to achieve accurate measurement of the dead layer thickness of high-purity germanium crystals.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] On the one hand, an automated photon scanning collimator for dead layer thickness of a germanium crystal is provided, which includes a lead chamber provided with a germanium crystal, a plexiglass plate rotatable relative to the lead chamber provided on the top of the lead chamber, a position-adjustable measurement component provided on the plexiglass plate, and an openable and closable lead cover for covering the plexiglass plate and the position-adjustable measurement component provided on the upper surface of the lead chamber;

[0007] The posture-adjustable measurement component includes a horizontal base, a slider, and a vertical metal frame; a trough for the vertical metal frame to pass through is provided on the organic glass plate; an L-shaped rotatable bracket passing through the vertical metal frame is provided at the lower end of the vertical metal frame; a photon generator is provided at the end of the L-shaped rotatable bracket; a support platform is provided at the top of the vertical metal frame, and a rotation angle adjuster is provided on the support platform; a transmission belt is provided on the rotation angle adjuster, and the other end of the transmission belt is located at the position where the L-shaped rotatable bracket passes through the vertical metal frame, so that the rotation angle adjuster can drive the L-shaped rotatable bracket 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 set on the organic glass plate; the upper surface of the horizontal base is provided with a first slide rail, and the front of the vertical metal frame is provided with a second slide rail; the lower surface of the slider matches the first slide rail and can slide left and right along the first slide rail to achieve left and right position adjustment of the photon generator; the back of the slider matches the second slide rail, and enables the vertical metal frame to slide up and down relative to the second slide rail to achieve up and down height adjustment of the photon generator.

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

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

[0011] Furthermore, a first position regulator and a second position regulator are provided on the slider; the first position regulator matches the first slide rail and is used to control the left and right movement of the slider; the second position regulator matches the second slide rail and is used to control the up and down movement of the vertical metal frame.

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

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

[0014] On the other hand, a method for measuring the dead layer thickness of a germanium crystal based on an automated photon scanning collimator for the dead layer thickness of a germanium crystal is provided, which comprises the following steps:

[0015] S1. Select the first measurement point at the center of the germanium crystal, adjust the position-adjustable measurement assembly so that the distance from the photon generator outlet to the upper surface of the germanium crystal is 2 cm and the photon incident angle is 90°, and record the corresponding peak area count (the peak area count can be analyzed from the measurement software);

[0016] S2. Adjust the position-adjustable measurement component so that the photon incident angle of the photon generator is 45°, and record the corresponding peak area counts;

[0017] S3, rotating organic glass plate, on the germanium crystal outer surface, to choose a measuring point every 5mm (the diameter of the circle along the crystal top (the diameter of the east to west and south to north of the regulation moves, the interval position 5mm)), repeat the measuring process of step S1 and step S2, record corresponding peak area count;

[0018] S4. Adjust the position-adjustable measurement assembly so that the photon generator outlet is 3 cm below the surface of the germanium crystal, the photons are emitted vertically toward the germanium crystal, and the photon generator outlet is 2 cm from the side of the germanium crystal. Record the corresponding peak area counts.

[0019] S5. Adjust the slider to move the photon generator toward the germanium crystal, select a measurement point every 5 mm of movement, and record the corresponding peak area count;

[0020] S6. Rotate the organic glass plate and repeat step S5 every 90°, recording the corresponding peak area counts;

[0021] S7. Obtain the dead layer thickness of the germanium crystal according to the recorded peak area counts.

[0022] Furthermore, the dead layer thickness calculation expression of the germanium crystal is (all measurement points require data at 90° and 45°, 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 in the direction of photon incident angle of 45° (divided by the measurement time), N 90 is the counting rate in the direction where the photon incident angle is 90°; μ Al 、μ Ge 、μ Be are the linear attenuation coefficients of aluminum, germanium, and beryllium, d Al d Be The linear attenuation coefficients of aluminum, germanium, and beryllium and their thicknesses are introduced here because photons need to pass through these materials before hitting the crystal. Changing the incident angle will also change the thickness of these materials.

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

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

[0027] Where E is the energy of different materials, including aluminum, germanium, and beryllium; μ is the linear attenuation coefficient of different materials; a, b, c, d, and e are all constants to be fitted.

[0028] Furthermore, when recording the peak area count at the same position, the peak area count was measured three times and the average value was taken as the peak area count corresponding to the position.

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

[0030] 1. It can measure the dead layer thickness of high-purity germanium crystals, solving the problem that the dead layer related parameters cannot be measured;

[0031] 2. The entire device is easy to process and install, and can achieve measurements in multiple directions. This method creatively uses the photon scanning method, which can further reduce costs and can achieve accurate measurement of the dead layer without disassembling the detector to expose the high-purity germanium crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the overall structure of the automated photon scanning collimator;

[0033] Figure 2 This is a schematic diagram of the lead chamber structure of the detector;

[0034] Figure 3 This is a schematic diagram of the posture-adjustable measurement component structure;

[0035] Among them: 1. Lead chamber; 2. Organic glass plate; 3. Position-adjustable measurement component; 4. Openable and closable lead cover; 5. Limiting platform; 6. Germanium crystal; 7. L-shaped rotatable bracket; 8. Photon emitter; 9. Vertical metal frame; 10. Horizontal base; 11. First slide rail; 12. First position regulator; 13. Second position regulator; 14. Slider; 15. Second slide rail; 16. Support platform; 17. Transmission belt; 18. Rotation angle regulator.

[0036] Figure 4 This is a schematic diagram of the structure of the automated photon scanning collimator in use;

[0037] Figure 5 This is a flow chart of the method for measuring the dead layer thickness of germanium crystal;

[0038] Figure 6 Schematic diagram of the measurement principle of the automated photon scanning collimator;

[0039] Figure 7 This is a model diagram of high-purity germanium crystal;

[0040] Figure 8 This is the dead layer influence curve of high purity germanium crystal. DETAILED DESCRIPTION

[0041] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0042] Example 1

[0043] Reference Figure 1-2 A germanium crystal dead layer thickness automated photon scanning collimator comprises a lead chamber 1 provided with a germanium crystal 6, a plexiglass plate 2 rotatable relative to the lead chamber 1 is provided on the top of the lead chamber 1, a position-adjustable measuring component 3 is provided on the plexiglass plate 2, an openable and closable lead cover 4 for covering the plexiglass plate 2 and the position-adjustable measuring component 3 is provided on the upper surface of the lead chamber 1; a limit platform 5 for limiting the shaking of the plexiglass plate 2 is provided on the upper surface of the lead chamber 1, and the plexiglass plate 2 is buckled on the limit platform 5; an angle scale and a spirit level are also provided on the upper surface of the lead chamber 1.

[0044] As a priority, refer to Figure 3 The position-adjustable measurement assembly 3 includes a horizontal base 10, a slider 14, and a vertical metal frame 9. Both the horizontal base 10 and the vertical metal frame 9 are provided with scales. A slot is provided on the organic glass 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, extending through the vertical metal frame 9. 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. A photon generator 8 is provided at the end of the L-shaped rotatable bracket 7. The photon source of the photon generator 8 is americium-241, and a collimator is provided at the front end of the photon source. A support platform 16 is provided on 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 position 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 to the germanium crystal 6;

[0045] The horizontal base 10 is set on the organic glass plate 2; the upper surface of the horizontal base 10 is provided with a first slide rail 11, and the front of the vertical metal frame 9 is provided with a second slide rail 15; 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 achieve left and right position adjustment of the photon generator 8; the back of the slider 14 matches the second slide rail 15, and enables the vertical metal frame 9 to slide up and down relative to the second slide rail 15 to achieve up and down height adjustment of the photon generator 8.

[0046] As a preferred embodiment, a first position regulator 12 and a second position regulator 13 are provided on the slider 14; the first position regulator 12 matches the first slide rail 11 and is used to control the left and right movement of the slider 14; the second position regulator 13 matches 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 automatic photon scanning collimator for the dead layer thickness of the germanium crystal provided in Example 1 specifically comprises the following steps:

[0049] Step 1: Design a dedicated photon scanning collimator for measuring the dead layer thickness of germanium crystals. Ensure that no photons leak outside the collimator. At a distance of 2 cm from the exit port, ensure that 96% of the emitted photons are concentrated within a diameter of 4 mm. This can be achieved by placing a transparent organic glass plate (PMMA) on the detector's lead shield, which can be moved on top of the lead shield. During measurement, the collimation position can be observed from the top. This allows for axial and radial movement and adjustment of the photon incident angle, which can be adjusted from 0 to 180 degrees. The photon collimator can be removed at any time and has an internal groove to secure the radiation source. This allows for movement during measurements of the dead layer on the side of a high-purity germanium crystal.

[0050] Step 2: Use photon transport software to build a detector model, change the dead layer thickness, set different energies of γ photons, and clarify the effect of the change of dead layer thickness on γ photons of different energies. The specific model and impact results are shown in Figure 7-8 , the analysis shows that the change of dead layer thickness has a greater impact on the counting rate of low-energy photons. The change of angle is equivalent to changing the thickness of the photons passing through the dead layer. Therefore, the use of low-energy photons (59.5keV) can better reflect the effect of the incident angle on the counting rate. 241 Am serves as the photon source this time.

[0051] Step 3: Remove the photon scanning collimator from the main device, then use a "Y"-shaped adjustable wrench to remove the lead cover above the collimator. Place the photon source into the chamber and secure it with the lead cover to ensure that the photon source does not move during the measurement process, thereby reducing the error introduced by scattering caused by the movement of the photon source.

[0052] Step 4: Reinstall the collimator into the main device, adjust the angle knob, adjust the incident angle of the photons, and use a spirit level to ensure that the current photon incident angle is 90°; place the entire device on the top of the detector lead chamber, and use a transparent organic glass plate to fix the position. Divide the organic glass plate into NS direction and WE direction respectively, radially adjust the position of the photon collimator and lock the position and the position of the organic glass plate, and ensure that the first measurement point is located in the center of the detector crystal. At this time, record the relative positions of the two scale lines adjusted 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, and ensure that the distance from the exit of the photon collimator to the upper surface of the detector crystal is 2 cm. Rotate the fixing button to lock the measurement height and record the positions of the scale lines adjusted up and down.

[0053] Step 5: Measure at the center point and record the peak area count. Measure three times and take the average, with each measurement lasting 7200 seconds. Adjust the angle knob so that the photon incident angle is 45°. Repeat the measurement three times and record the peak area count. Record a point every 5 mm along the NS and WE directions defined on the detector crystal surface, and repeat the measurement process.

[0054] Step 6: Axially adjust the photon collimator so that the photon collimator outlet is 3 cm below the detector surface, adjust the photon exit angle so that the photons can reach the side dead layer of the detector crystal vertically, and fix the axial position and angular position respectively; adjust the radial knob so that the distance from the photon collimator outlet 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 the four directions of N, S, W and E respectively, and repeat the measurement process.

[0055] Step 7: Using the XCOM database, the mass attenuation coefficients of materials such as Al, Ge, and Be at different energies are obtained, and a set of data of E (energy) - μ (mass attenuation coefficient) under different materials is obtained. The natural logarithm of the data is taken, and a fourth-order polynomial fitting is used to obtain the fitting curve and fitting parameters, thereby realizing the fitting output of the mass attenuation coefficients 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 indexed to achieve the interpolation of the target energy.

[0059] Step 8: Calculate the dead layer thickness using the counting rates at 45° and 90° and the following formula:

[0060]

[0061] Among them, N 45 is the count rate when collimated at 45°, N 90 is the count rate in the 90° direction, μ Al 、μ Ge 、μ Be are the linear attenuation coefficients of aluminum, germanium, and beryllium, d Al d Be are the thicknesses of aluminum and beryllium, respectively, where d Ge is the thickness of the dead layer of the germanium detector; this formula can be extended to any angle.

[0062]

[0063] Taking the natural logarithm of the above formula:

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

[0065]

[0066] In summary, the present invention has developed an automated photon scanning collimator for the dead layer thickness of high-purity germanium crystals. Based on this, a method for measuring the dead layer thickness of high-purity germanium crystals is innovatively proposed to achieve accurate measurement of the dead layer thickness.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0068] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A germanium crystal dead layer thickness automatic photon scanning collimator, characterized in that: The invention comprises an organic glass plate (2) arranged on the top of a lead chamber (1) and rotatable relative to the lead chamber (1), a position-adjustable measuring component (3) being arranged on the organic glass plate (2), and an openable and closable lead cover (4) for covering the organic glass plate (2) and the position-adjustable measuring component (3) being arranged on the upper surface of the lead chamber (1); The posture-adjustable measurement assembly (3) comprises a horizontal base (10), a slider (14) and a vertical metal frame (9); a groove for the vertical metal frame (9) to pass through is provided on the organic glass plate (2); an L-shaped rotatable bracket (7) passing through the vertical metal frame (9) 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 position 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) to the germanium crystal (6) in the lead chamber (1); A horizontal base (10) is arranged on an organic glass plate (2); a first slide rail (11) is arranged on the upper surface of the horizontal base (10), and a second slide rail (15) is arranged on the front surface of a vertical metal frame (9); a lower surface of a slider (14) matches the first slide rail (11) and can slide left and right along the first slide rail (11) to achieve left and right position adjustment of a photon generator (8); a back surface of the slider (14) matches the second slide rail (15) and enables the vertical metal frame (9) to slide up and down relative to the second slide rail (15) to achieve up and down height adjustment of the photon generator (8).

2. The automatic photon scanning collimator for dead layer thickness of germanium crystal 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 where the vertical metal frame (9) is located.

3. The automatic photon scanning collimator for dead layer thickness of germanium crystal according to claim 1, characterized in that: Scales are provided on the horizontal base (10) and the vertical metal frame (9).

4. The automatic photon scanning collimator for dead layer thickness of germanium crystal according to claim 1, characterized in that: A first position regulator (12) and a second position regulator (13) are provided on the slider (14); the first position regulator (12) matches the first slide rail (11) and is used to control the left and right movement of the slider (14); the second position regulator (13) matches the second slide rail (15) and is used to control the up and down movement of the vertical metal frame (9).

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

6. The automatic photon scanning collimator for dead layer thickness of germanium crystal according to claim 1, characterized in that: The upper surface of the lead chamber (1) is provided with a limit platform (5) for limiting the shaking of the organic glass plate (2), and the organic glass plate (2) is buckled on the limit 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 the automatic photon scanning collimator for the dead layer thickness of a germanium crystal according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Select the first measurement point at the center of the germanium crystal (6), adjust the position-adjustable measurement component (3) so that the distance between the output port of the photon generator (8) and the upper surface of the germanium crystal (6) is 2 cm and the photon incident angle is 90°, and record the corresponding peak area count; S2. Adjust the position-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, rotating the organic glass plate (2), selecting a measurement point at intervals of 5 mm on the outer surface of the germanium crystal (6) in the designated NS direction and WE direction, repeating the measurement process of step S1 and step S2, and recording the corresponding peak area counts; S4. Adjust the position-adjustable measurement component (3) so that the output port of the photon generator (8) is located 3 cm below the surface of the germanium crystal (6), the photons are emitted vertically toward the germanium crystal (6), and the output port of the photon generator (8) is 2 cm away from the side of the germanium crystal (6), and 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, rotating the organic glass plate (2), repeating step S5 every time the rotation is 90 degrees, and recording the corresponding peak area counts; S7. Obtain the dead layer thickness of the germanium crystal (6) according to the recorded peak area counts.

8. The method for measuring the thickness of the dead layer of germanium crystal according to claim 7, characterized in that: The calculation expression of the dead layer thickness of germanium crystal (6) is: 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 in the direction of photon incident angle of 45°, N 90 is the counting rate in the direction where the photon incident angle is 90°; μ Al 、μ Ge 、μ Be are the linear attenuation coefficients of aluminum, germanium, and beryllium, d Al d Be are the thicknesses of aluminum and beryllium, respectively.

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

10. The method for measuring the thickness of the dead layer of germanium crystal according to claim 7, characterized in that: When recording the peak area count at the same position, measure it three times and take the average value as the peak area count corresponding to that position.

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