A high-precision characterization method for rounded corner high-purity germanium detectors

Abstract

The present invention discloses a high-precision characterization method for a rounded corner high-purity germanium detector, including the following steps: 1. constructing a 3D model of the high-purity germanium detector; 2. selecting specific energy rays for Monte Carlo sampling simulation; 3. determining the direction of adjusting the parameters of the outer dead layer and performing model adjustment and Monte Carlo simulation; 4. selecting a set of parameter values ​​closest to the actual experimental data as the benchmark characterization of the high-purity germanium detector; 5. performing non-uniform adjustment and Monte Carlo simulation of the dead layer at the rounded corner; 6. selecting a set of parameter values ​​closest to the actual experimental data at this time as the high-precision characterization of the high-purity germanium detector. The present invention realizes the accurate modeling of the high-purity germanium detector, especially the establishment of a model for the crystal of the rounded corner part, and the corresponding correction of the rounded corner dead layer, thereby reducing the inaccuracy of the simulation results of the high-purity germanium detector at the low energy end.

Description

Technical Field

[0001] The invention belongs to the technical field of high-purity germanium detector characterization, and in particular relates to a high-precision characterization method for a rounded-corner high-purity germanium detector. Background Art

[0002] The top of the germanium crystal in the high-purity germanium detector often has a rounded structure. However, during the modeling or characterization adjustment process of the existing high-purity germanium detector, the dead layer thickness and morphology outside the germanium crystal are variable, resulting in the external structure modeling and Monte Carlo characterization of the high-purity germanium detector being adjusted along with the changes in the internal germanium crystal modeling and Monte Carlo characterization, which in turn causes the modeling and Monte Carlo characterization of the high-purity germanium detector to be too complicated. Therefore, the modeling of the germanium crystal inside the high-purity germanium detector usually uses a regular cylinder to characterize its germanium crystal structure. When traditional germanium crystal modeling and characterization of germanium crystals, the modeling of the rounded parts is usually ignored. Such a modeling method will increase the volume of the germanium crystal, which will have a greater impact on the detection efficiency of gamma photons at the low-energy end, resulting in a certain deviation between the simulation results and the experimental results. Such a deviation will be brought into the characterization of the detector structure, making the characterization of the detector structure inaccurate. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a high-precision characterization method for a rounded-corner high-purity germanium detector in view of the deficiencies in the above-mentioned prior art. The introduction of rounded-corner dead layer correction will greatly improve the characterization accuracy of the detector, and the model will be closer to the actual parameters of the detector, which is convenient for promotion and use.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a high-precision characterization method for rounded corner high-purity germanium detector, characterized in that the method comprises the following steps:

[0005] Step 1, construct a 3D model of a high-purity germanium detector: the 3D model of the high-purity germanium detector includes a 3D model of a germanium crystal and a 3D model of the external structure of the high-purity germanium detector; the 3D model of the germanium crystal includes a germanium crystal, an outer dead layer attached to the outside of the germanium crystal, and an inner dead layer attached to the cold finger hole in the germanium crystal; the outer dead layer includes a top dead layer, a lateral dead layer, and a fillet dead layer connecting the top dead layer and the lateral dead layer;

[0006] Given the initial thickness of the top dead layer, the fillet dead layer, the lateral dead layer and the inner dead layer, a 3D model of the high purity germanium detector is constructed;

[0007] Step 2: Select specific energy rays to perform Monte Carlo sampling simulation;

[0008] Step 3, determine the adjustment direction of the outer dead layer parameters and perform model adjustment and Monte Carlo simulation;

[0009] Step 4: Select a set of parameter values ​​that are closest to the actual experimental data as the benchmark characterization of the high purity germanium detector;

[0010] Step 5: Non-uniform adjustment of the dead layer at the fillet and Monte Carlo simulation;

[0011] Step 6: Select a set of parameter values ​​that are closest to the actual experimental data at this time as the high-precision characterization of the high-purity germanium detector.

[0012] The above-mentioned high-precision characterization method of a rounded-corner high-purity germanium detector is characterized in that: in step one, the 3D model of the germanium crystal is constructed by compression, pulling and shell extraction using SoildWorks software; the cold finger hole inside the germanium crystal is cut out by pulling to form a hollow cylinder at the bottom of the germanium crystal, and then a hemispherical structure is constructed at the top of the hollow cylinder, and a corresponding model of the inner dead layer is established in the cold finger hole. During the model building process, a corresponding STL file is formed; the 3D model of the external structure of the high-purity germanium detector is established using C++ language.

[0013] The above-mentioned high-precision characterization method of a rounded-corner high-purity germanium detector is characterized in that: in step 2, the germanium crystal 3D model constructed by SoildWorks and the high-purity germanium detector external structure 3D model established by C++ language are imported into Geant4 through model conversion to select specific energy rays for sampling simulation.

[0014] The high-precision characterization method of the rounded corner high-purity germanium detector is characterized in that: in step three, the detection efficiency result obtained by simulation is compared with the detection efficiency result measured by the actual experiment. When the efficiency calibration curve obtained by simulation is below the efficiency calibration curve obtained by the actual experiment, the outer dead layer parameters need to be thickened and adjusted; when the efficiency calibration curve obtained by simulation is above the efficiency calibration curve obtained by the actual experiment, the outer dead layer parameters need to be thinned and adjusted;

[0015] The outer contour line size of the germanium crystal 3D model remains unchanged. When the outer dead layer parameters are adjusted to be thicker, that is, the contact portion between the germanium crystal and the outer dead layer is adjusted, the germanium crystal is adjusted to be thinner accordingly.

[0016] When the outer dead layer parameters are adjusted to be thin, that is, the contact portion between the germanium crystal and the outer dead layer is adjusted, the germanium crystal is adjusted to be thickened accordingly;

[0017] The 3D model of the external structure of the high-purity germanium detector built in C++ language does not need to be modified during the whole process;

[0018] The 3D model of germanium crystal after multiple adjustments was constructed using SoildWorks, and then imported into Geant4 through model conversion to simulate particle sampling to obtain the data of ray energy and the corresponding detection efficiency, and form the corresponding efficiency calibration curve corresponding to the detection efficiency and energy.

[0019] The high-precision characterization method for a rounded-corner high-purity germanium detector is characterized in that the thickness step length of the outer dead layer parameter thickening adjustment or thinning adjustment is 1 mm.

[0020] The above-mentioned high-precision characterization method for rounded-corner high-purity germanium detectors is characterized in that: in step four, the data of the radiation energy and the corresponding detection efficiency obtained by multiple simulations in step three are compared with the data obtained from actual experiments to obtain a detection efficiency curve closest to that obtained from actual experiments. At this time, the outer dead layer parameters can be determined, and the set of parameter values ​​closest to the detection efficiency curve obtained from actual experiments is selected as the benchmark characterization of the high-purity germanium detector.

[0021] The above-mentioned high-precision characterization method of a rounded corner high-purity germanium detector is characterized in that: in step five, during the non-uniform adjustment of the dead layer of the rounded corner, non-uniform fine-adjustment is performed on the contact portion between the germanium crystal and the dead layer of the rounded corner, wherein the outer contour line size of the germanium crystal 3D model remains unchanged.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The present invention realizes accurate modeling of high-purity germanium detectors, especially establishes a model for the crystal of the rounded corners, makes corresponding corrections to the rounded corner dead layer, and reduces the inaccuracy of the simulation results when simulating the high-purity germanium detector at the low energy end.

[0024] 2. The present invention realizes relatively easy modification of the detector model by combining SoildWorks and C++. Each time the model is adjusted, the accuracy of the modeling can be judged in a timely manner on the QT interface. If there is a problem, it can be adjusted in time, ensuring the rigor of the data obtained from each simulation.

[0025] 3. The method of the present invention has simple steps, realizes the modeling of the coordination between the crystal and the dead layer, and makes the inner fillet of the dead layer fit tightly with the outer fillet of the crystal, which is closer to the actual situation that the dead layer of a real high-purity germanium detector increases in thickness with the increase of service life. In the structural characterization of the high-purity germanium detector, the characterization process is simpler and faster, the characterization results are more accurate, and it is easy to promote and use.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure is a flowchart of the method of the present invention.

[0028] Figure 2 It is a schematic diagram of the structural section of the germanium crystal of the present invention.

[0029] Description of reference numerals:

[0030] 1—top dead layer; 2—rounded dead layer; 3—lateral dead layer;

[0031] 4—Germanium crystal; 5—Inner dead layer; 6—Cold finger hole. DETAILED DESCRIPTION

[0032] like Figure 1 and Figure 2 As shown, a high-precision characterization method for a rounded-corner high-purity germanium detector of the present invention comprises the following steps:

[0033] Step 1, construct a 3D model of a high-purity germanium detector: the 3D model of the high-purity germanium detector includes a 3D model of a germanium crystal and a 3D model of the external structure of the high-purity germanium detector; the 3D model of the germanium crystal includes a germanium crystal 4, an outer dead layer attached to the outside of the germanium crystal 4, and an inner dead layer 5 attached to the cold finger hole 6 in the germanium crystal 4; the outer dead layer includes a top dead layer 1, a lateral dead layer 3, and a fillet dead layer 2 connecting the top dead layer 1 and the lateral dead layer 3;

[0034] A 3D model of a high-purity germanium detector is constructed by giving the initial thicknesses of the top dead layer 1, the fillet dead layer 2, the lateral dead layer 3 and the inner dead layer 5;

[0035] It should be noted that "high purity" means that the purity of the metal material is above 99.999%. There is a germanium crystal inside the high purity germanium detector, but there is a dead layer on the outer surface of the germanium crystal and on the surface of the internal cold finger hole. The dead layer will become thicker over time. The increase of the dead layer will have a greater impact on the detection efficiency, so it is very important to estimate the thickness of the dead layer.

[0036] Step 2: Select specific energy rays to perform Monte Carlo sampling simulation;

[0037] Step 3, determine the adjustment direction of the outer dead layer parameters and perform model adjustment and Monte Carlo simulation;

[0038] Step 4: Select a set of parameter values ​​that are closest to the actual experimental data as the benchmark characterization of the high purity germanium detector;

[0039] Step 5: Non-uniform adjustment of the dead layer at the fillet and Monte Carlo simulation;

[0040] It should be noted that, since the diffusion of the dead layer is random, it is necessary to adjust the dead layer of the rounded corner non-uniformly.

[0041] Step 6: Select a set of parameter values ​​that are closest to the actual experimental data at this time as the high-precision characterization of the high-purity germanium detector.

[0042] In this embodiment, in step one, the 3D model of the germanium crystal is constructed using SoildWorks software through compression, pulling and shell extraction; the cold finger hole 6 inside the germanium crystal 4 is cut out by pulling to form a hollow cylinder at the bottom of the germanium crystal 4, and then a hemispherical structure is constructed at the top of the hollow cylinder, and a corresponding model of the inner dead layer 5 is established in the cold finger hole 6. During the model building process, a corresponding STL file is generated; the 3D model of the external structure of the high-purity germanium detector is established using C++ language.

[0043] In this embodiment, in step 2, the germanium crystal 3D model constructed by SoildWorks and the 3D model of the external structure of the high-purity germanium detector established by C++ language are imported into Geant4 through model conversion to select specific energy rays for sampling simulation.

[0044] In this embodiment, in step three, the detection efficiency result obtained by simulation is compared with the detection efficiency result measured by actual experiment. When the efficiency calibration curve obtained by simulation is below the efficiency calibration curve obtained by actual experiment, the outer dead layer parameter needs to be thickened and adjusted; when the efficiency calibration curve obtained by simulation is above the efficiency calibration curve obtained by actual experiment, the outer dead layer parameter needs to be thinned and adjusted;

[0045] The outer contour line size of the germanium crystal 3D model remains unchanged. When the outer dead layer parameters are adjusted to be thicker, that is, the contact portion between the germanium crystal and the outer dead layer is adjusted, the germanium crystal 4 is adjusted to be thinner accordingly.

[0046] When the outer dead layer parameters are adjusted to be thinned, that is, the contact portion between the germanium crystal and the outer dead layer is adjusted, the germanium crystal 4 is adjusted to be thickened accordingly;

[0047] The 3D model of the external structure of the high-purity germanium detector built in C++ language does not need to be modified during the whole process;

[0048] The 3D model of germanium crystal after multiple adjustments was constructed using SoildWorks, and then imported into Geant4 through model conversion to simulate particle sampling to obtain the data of ray energy and the corresponding detection efficiency, and form the corresponding efficiency calibration curve corresponding to the detection efficiency and energy.

[0049] In this embodiment, the thickness step length of the outer dead layer parameter thickening adjustment or thinning adjustment is 1 mm.

[0050] In this embodiment, in step four, the data of the ray energy and the corresponding detection efficiency obtained from multiple simulations in step three are compared with the data obtained from the actual experiment to obtain a detection efficiency curve closest to the actual experiment. At this time, the outer dead layer parameters can be determined, and the set of parameter values ​​closest to the detection efficiency curve obtained from the actual experiment is selected as the benchmark characterization of the high-purity germanium detector.

[0051] In this embodiment, in step five, during the non-uniform adjustment of the dead layer at the rounded corner, non-uniform fine adjustment is performed on the contact portion between the germanium crystal 4 and the dead layer 2 at the rounded corner, wherein the outer contour line size of the germanium crystal 3D model remains unchanged.

[0052] It should be noted that the Monte Carlo simulation after the non-uniform adjustment of the dead layer at the fillet is the same as the Monte Carlo simulation process after determining the adjustment direction of the outer dead layer parameters and adjusting the model in step three.

[0053] When the present invention is used, SolidWorks and C++ are used to realize the joint construction of the Geant4 model. Specifically, SolidWorks realizes the modeling of the germanium crystal of the transformation part, and C++ realizes the modeling of the external fixed structure part of the detector germanium crystal. This construction method makes the modeling more simple, fast and accurate during the subsequent dead layer correction simulation. For the established solid model, the model file is imported into Geant4 according to the actual situation and displayed in the QT window to confirm the accuracy of the external features of the model and its correctness compared to the physical position of the detector. By setting the vis macro file, the QT viewing angle and the color of the physical model are set to a mode that is relatively easy to observe.

[0054] In this embodiment, for the established physical model, when sampling particles, the sampling area should be limited to the range of the established model through commands, so as to ensure that the simulation effect is close to the particle emission effect of the actual experiment.

[0055] In this embodiment, by setting different energy gradients and different physical model center coordinate positions, multiple Monte Carlo simulations are performed to obtain detection efficiencies at different energies and different positions, and an efficiency calibration curve is fitted.

[0056] The modeling process is divided into three parts: the external dead layer of the crystal, the internal dead layer of the crystal, and the germanium crystal itself. The construction process of the external dead layer of the crystal is: first draw a circle with a set radius in the Solidworks modeling interface, and then pull it up. After the pull is completed, it is shelled inward, and then a dead layer structure close to the real detector crystal is obtained by setting fillets on the top. Figure 2As shown). Then, the same method is used to build the dead layer of the cold finger hole inside the crystal (the thickness of the inner dead layer is several hundred microns, so no pictures are shown). The last step is to model the crystal. The cylinder used to build the outer dead layer model at the beginning is used for modeling. Its height and the radius of the bottom circle need to be adjusted accordingly according to the thickness of the dead layer. After the adjustment, pull up and cut out the cold finger hole inside. A fillet is formed on the outside, and the arc of the fillet needs to match the inner fillet of the outer dead layer. At this point, the three models are built. Save the three models as different STEP type files, then import them into FreeCAD, mesh the models, and then save them as STL type files. Import the three models into Geant4, set their positions, and then rotate or translate the models according to the actual situation, and then combine the C++ modeling method to model the detector shell. Then, according to the ordinary Geant4 modeling process, write the corresponding code for each file module such as logicVolume and physicVolume. Thereby, the physical model of the target object is established in Geant4. After that, the size, position, direction and other details of the established model can be confirmed according to QT. After confirming that it is the same as expected, the particle sampling part is implemented, and simulation is performed using different energies (the selected energy value must be consistent with the energy of the radiation source used in the actual efficiency calibration in the laboratory) to obtain the efficiency calibration curve corresponding to energy and efficiency.

[0057] After obtaining the efficiency calibration curve obtained by the preliminary simulation, it is necessary to use point sources of different energies and known radioactivity to measure the high-purity germanium detectors of the required calibration to obtain the efficiency calibration curve corresponding to energy and efficiency. According to the relevant experience of previous detection efficiency correction and the actual detector situation (the length of time the detector is used), the corresponding top dead layer thickness and side dead layer thickness adjustment step are set. It is usually recommended to set this step to 0.2mm. Then, according to this step, the above-established model is adjusted to be thickened or thinned, and the adjustment range is 0.7mm-1.5mm. Then, each group of models established according to this step replaces the original crystal model in Geant4 in turn, and repeats the above simulation sampling process. The detection efficiency results obtained by each group of energy sampling are compared with the detection efficiency data actually measured in the laboratory again. Select the dead layer parameters corresponding to the group of data closest to the laboratory measured (if the experimental data is close to the two groups of simulation data at the same distance, the dead layer parameters corresponding to the two groups of simulation data are retained at the same time), and then adjust the parameters of the fillet part in the next step.

[0058] Since the diffusion process of the particles forming the dead layer is irregular, the radius size can be corrected accordingly in the rounded part. According to the detector model constructed with the selected parameters, the rounded corners of the inner arc surface of the dead layer and the outer arc surface of the crystal are adjusted at the same time. Since the adjustment of the radius of the dead layer fillet and the crystal fillet has little effect on the detection efficiency, when establishing the crystal and the external dead layer, the radius of the inner fillet of the dead layer is adjusted in steps of 5 mm at the same time as the radius of the outer fillet of the crystal. A range of ±25mm is selected to form 10 groups of models with different radius parameters, and then simulation calculations are performed separately. In this simulation experiment, the order of magnitude of the sampling number of 2 particles needs to be increased to ensure that the uncertainty of the sampling results remains within an acceptable range. After obtaining the sampling results, they are compared with the physical experiment, and the best set of radius parameters are selected as the basic parameters for adjusting the non-uniform fillet parameters of the crystal fillet and the dead layer fillet. The size of the non-uniformity is adjusted in steps of 1mm (for example, the original rounded half angle is 5cm, and now it is set to a radius of 4.9cm perpendicular to the top dead layer and a radius of 4.8cm perpendicular to the lateral dead layer). According to such refined adjustments, the actual structural parameters of the dead layer outside the detector can be obtained. The non-uniformity adjustment is to establish a 3*3 group of models formed by adjusting the two parameters of the radius perpendicular to the top dead layer and the radius perpendicular to the lateral dead layer in steps of 1mm. After the model is established, a simulation calculation is performed according to the above-mentioned simulation method. Finally, a crystal model established by a set of crystal parameter data is obtained. The efficiency calibration curve simulated by particle sampling is closest to the efficiency calibration curve obtained by the real experiment. This set of crystal parameters can be considered as the accurate characterization parameters of the crystal structure of the detector.

[0059] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A high-precision characterization method for a rounded-corner high-purity germanium detector, characterized in that: The method comprises the following steps: Step 1, constructing a 3D model of a high-purity germanium detector: the 3D model of the high-purity germanium detector includes a 3D model of a germanium crystal and a 3D model of an external structure of the high-purity germanium detector; the 3D model of the germanium crystal includes a germanium crystal (4), an outer dead layer attached to the outside of the germanium crystal (4), and an inner dead layer (5) attached to a cold finger hole (6) in the germanium crystal (4); the outer dead layer includes a top dead layer (1), a lateral dead layer (3), and a fillet dead layer (2) connecting the top dead layer (1) and the lateral dead layer (3); A 3D model of a high-purity germanium detector is constructed by giving the initial thicknesses of a top dead layer (1), a fillet dead layer (2), a lateral dead layer (3) and an inner dead layer (5); Step 2: Select specific energy rays to perform Monte Carlo sampling simulation; Step 3, determine the adjustment direction of the outer dead layer parameters and perform model adjustment and Monte Carlo simulation; Step 4: Select a set of parameter values ​​that are closest to the actual experimental data as the benchmark characterization of the high purity germanium detector; Step 5: Non-uniform adjustment of the dead layer at the fillet and Monte Carlo simulation; Step 6: Select a set of parameter values ​​that are closest to the actual experimental data at this time as the high-precision characterization of the high-purity germanium detector.

2. A high-precision characterization method for a rounded corner high-purity germanium detector according to claim 1, characterized in that: In step 1, the 3D model of the germanium crystal is constructed by compression, pulling and shell extraction using SoildWorks software; the cold finger hole (6) inside the germanium crystal (4) is removed by pulling to form a hollow cylinder at the bottom of the germanium crystal (4), and then a hemispherical structure is constructed at the top of the hollow cylinder, and a corresponding model of the inner dead layer (5) is established in the cold finger hole (6). During the model building process, a corresponding STL file is generated; The 3D model of the external structure of the high-purity germanium detector was established using C++ language.

3. A high-precision characterization method for a rounded corner high-purity germanium detector according to claim 2, characterized in that: In step 2, the 3D model of the germanium crystal constructed by SoildWorks and the 3D model of the external structure of the high-purity germanium detector established by C++ language are imported into Geant4 through model conversion to select specific energy rays for sampling simulation.

4. A high-precision characterization method for a rounded corner high-purity germanium detector according to claim 3, characterized in that: In step three, the detection efficiency results obtained by simulation are compared with the detection efficiency results measured by actual experiments. When the efficiency calibration curve obtained by simulation is below the efficiency calibration curve obtained by actual experiments, the outer dead layer parameters need to be thickened and adjusted; when the efficiency calibration curve obtained by simulation is above the efficiency calibration curve obtained by actual experiments, the outer dead layer parameters need to be thinned and adjusted; The outer contour line size of the germanium crystal 3D model remains unchanged. When the outer dead layer parameters are adjusted to be thicker, that is, the contact portion between the germanium crystal and the outer dead layer is adjusted, the germanium crystal (4) is adjusted to be thinner accordingly. When the outer dead layer parameters are adjusted to be thinner, that is, the contact portion between the germanium crystal and the outer dead layer is adjusted, the germanium crystal (4) is adjusted to be thicker accordingly; The 3D model of the external structure of the high-purity germanium detector built in C++ language does not need to be modified during the whole process; The 3D model of germanium crystal after multiple adjustments was constructed using SoildWorks, and then imported into Geant4 through model conversion to simulate particle sampling to obtain the data of ray energy and the corresponding detection efficiency, and form the corresponding efficiency calibration curve corresponding to the detection efficiency and energy.

5. A high-precision characterization method for a rounded corner high-purity germanium detector according to claim 4, characterized in that: The thickness step length of the outer dead layer parameter thickening adjustment or thinning adjustment is 1 mm.

6. A high-precision characterization method for a rounded corner high-purity germanium detector according to claim 4, characterized in that: In step four, the radiation energy obtained from multiple simulations in step three and the corresponding detection efficiency data are compared with the data obtained from the actual experiment to obtain a detection efficiency curve closest to the actual experiment. At this time, the outer dead layer parameters can be determined, and the set of parameter values ​​closest to the detection efficiency curve obtained from the actual experiment is selected as the benchmark characterization of the high-purity germanium detector.

7. A high-precision characterization method for a rounded corner high-purity germanium detector according to claim 4, characterized in that: In step 5, during the non-uniform adjustment of the dead layer at the rounded corner, non-uniform fine adjustment is performed on the portion where the germanium crystal (4) and the dead layer (2) at the rounded corner are in contact, wherein the outer contour line size of the germanium crystal 3D model remains unchanged.

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