Scintillator detector

Abstract

The invention discloses a scintillator detector which comprises a first photomultiplier, a second photomultiplier, a scintillation light-emitting crystal, a first signal processing circuit, a second signal processing circuit and a pulse signal adding circuit. The flickering light-emitting crystal is in the shape of a circular truncated cone, the included angle between the side face and the bottom face of the circular truncated cone is 85 degrees, the first photomultiplier and the second photomultiplier are coupled with the top face and the bottom face of the flickering light-emitting crystal respectively, and the first signal processing circuit is electrically connected with the first photomultiplier. The second signal processing circuit is electrically connected with the second photomultiplier, and the pulse signal adding circuit is electrically connected with the first signal processing circuit and the second signal processing circuit. Due to the adoption of the technical scheme, compared with the prior art, the photon collection efficiency and the light collection uniformity are improved, and the energy resolution of the scintillator detector is further improved.

Description

Technical Field

[0001] The present invention relates to the field of scintillation detectors, and particularly to a scintillation detector. Background Art

[0002] High-detection-efficiency and high-energy-resolution detectors are widely used in fields such as deep space and deep sea exploration, large scientific projects, and homeland security. They not only support scientific frontier exploration but also greatly affect national strategic security. The energy resolution of a detector is defined as the ratio of the full width at half maximum of the characteristic peak in the differential pulse amplitude distribution spectrum (referred to as the energy spectrum) of the detector to the pulse amplitude corresponding to the peak, denoted by δ: δ = ΔE / E; energy resolution is one of the very important performance indicators of a detector.

[0003] For a scintillation detector, the factors affecting the energy resolution can be described by formula (1):

[0004] δ 2 =(ΔE / E) 2 = (δsc) 2 +(δp) 2 +(δst) 2 +(δn) 2 (1)

[0005] Where δsc is the intrinsic resolution of the crystal, which is mainly related to the non-proportional response of the scintillator and the inhomogeneity in the scintillator, and depends on the performance of the crystal itself; δp is the transfer resolution, which depends on the optical coupling quality between the crystal and the photoelectric conversion device, light collection, response uniformity, and uniformity of the photoelectron collection efficiency; δst is the statistical contribution of the photoelectric conversion, which is related to the photoelectric conversion and the photoelectron collection efficiency, and depends on the light output of the crystal, the photon detection efficiency, and its multiplication performance; δn is the contribution of the electronic noise. Currently, commonly used detectors include gas detectors, scintillation detectors, and semiconductor detectors. Scintillation detection has been widely used due to its high detection efficiency and less demanding operating conditions. However, relatively speaking, its energy resolution is the worst among the three, which limits its application in some fields. Among scintillation detectors, due to the high luminescence efficiency of LaBr3(Ce) crystals and the highest intrinsic resolution of the crystals, it has the best energy resolution among scintillation detectors. In order to maximize the energy resolution of LaBr3(Ce) detectors and expand their application fields, the present invention aims at the relationship between the energy resolution and its light collection efficiency and light collection uniformity, and in order to achieve the goal of improving the energy resolution, the detector is optimized and the photon collection method is improved.

[0006] Currently, general scintillation detectors usually adopt cylindrical scintillating crystals, and the photon collection method adopts single-end collection, such as Figure 1As shown. The disadvantage of this scintillator detector is that photons exit from one end face of the crystal and hit the optoelectronic device. Since photons are absorbed and attenuated due to the self - absorption of the crystal during propagation in the scintillator crystal, a part of the fluorescent photons generated by the scintillator cannot be collected, resulting in a low photon collection efficiency. The difference in the paths traveled by photons emitted from different locations in the scintillator crystal leads to a difference in absorption attenuation due to self - absorption, resulting in poor light collection uniformity. Summary of the Invention

[0007] The present application provides a scintillator detector to solve the problems of low photon collection efficiency and poor light collection uniformity of existing scintillator detectors.

[0008] To achieve the above - mentioned purpose, the present application adopts the following technical solutions.

[0009] A scintillator detector includes a first photomultiplier tube, a second photomultiplier tube, a scintillating crystal, a first signal processing circuit, a second signal processing circuit, and a pulse signal adding circuit; the shape of the scintillating crystal is a frustum of a cone with an included angle of 85° between the side face and the bottom face. The first photomultiplier tube and the second photomultiplier tube are respectively coupled to the top face and the bottom face of the scintillating crystal. The first signal processing circuit is electrically connected to the first photomultiplier tube, the second signal processing circuit is electrically connected to the second photomultiplier tube, and the pulse signal adding circuit is electrically connected to the first signal processing circuit and the second signal processing circuit respectively.

[0010] In some embodiments, both the first photomultiplier tube and the second photomultiplier tube are silicon photomultiplier tubes.

[0011] In some embodiments, the scintillating crystal is a cerium - doped lanthanum bromide crystal.

[0012] The present application has at least the following technical effects or advantages: Compared with a cylindrical shape, when the scintillating crystal adopts a frustum of a cone with an included angle of 85° between the side face and the bottom face, since the propagation path of photons in the scintillator crystal becomes shorter, the absorption attenuation caused by the self - absorption of the crystal decreases, thereby improving the photon collection efficiency. On the other hand, since the difference in the paths traveled by photons emitted from different locations in the scintillator crystal becomes smaller, the difference in absorption attenuation caused by the self - absorption of the crystal decreases, thereby improving the light collection uniformity. Since both the photon collection efficiency and the light collection uniformity are improved, the energy resolution of the scintillator detector is further improved. Brief Description of the Drawings

[0013] Figure 1 It is a schematic structural diagram of a scintillator detector in an embodiment of the present application;

[0014] Figure 2Schematic diagram of the light collection efficiency corresponding to scintillating crystals of different shapes in an embodiment of the present application;

[0015] Figure 3 Variation diagram of light collection uniformity after light emission at different positions of scintillating crystals of different shapes in an embodiment of the present application;

[0016] Figure 4 Comparison diagram of the relative light collection efficiency of single / double-sided signal readout of scintillating crystals of different shapes in an embodiment of the present application;

[0017] Figure 5 Comparison diagram of the simulation and experimental data of the relative light collection efficiency of double-sided signal readout of scintillating crystals of different shapes in an embodiment of the present application.

[0018] Figure 6 Comparison diagram of the simulation and experimental data of the percentage increase in the light collection efficiency of double-sided signal readout relative to single-sided signal readout of scintillating crystals of different shapes in an embodiment of the present application. Specific embodiments

[0019] To better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0020] Embodiment 1

[0021] Refer to Figure 1 , a scintillator detector, including a first photomultiplier tube 1, a second photomultiplier tube 2, a scintillating crystal 3, a first signal processing circuit 4, a second signal processing circuit 5, and a pulse signal addition circuit 6. The shape of the scintillating crystal 3 is a frustum of a cone with an angle of 85° between the side surface and the bottom surface. The first photomultiplier tube 1 and the second photomultiplier tube 2 are respectively coupled to the top surface and the bottom surface of the scintillating crystal 3. The first signal processing circuit 4 is electrically connected to the first photomultiplier tube 1. The second signal processing circuit 5 is electrically connected to the second photomultiplier tube 2. The pulse signal addition circuit 6 is respectively electrically connected to the first signal processing circuit 3 and the second signal processing circuit 4.

[0022] Preferably, in this embodiment, both the first photomultiplier tube 1 and the second photomultiplier tube 2 are silicon photomultiplier tubes (SIPM). The scintillating crystal 3 is a cerium-doped lanthanum bromide crystal, i.e., LaBr3(Ce) scintillation crystal.

[0023] In view of the deficiencies that the single-end output of scintillator fluorescence photons increases self-absorption due to the longer path of photons, resulting in lower photon collection efficiency and poor light collection uniformity, the present invention optimizes from the crystal structure. In this study, first, the photon collection efficiency was studied. Geant4 was used to expand the shape selection on the basis of a Φ76.2mm x 76.2mm cylinder, and frustum of a cone, cuboid, and cube were tried.

[0024] For the frustum of a cone, the light output situations at different angles of 85°, 80°, 75°, 70°, and 65° were simulated. The inclination angle θ of the frustum of a cone is defined as the angle formed by the bottom surface and the side surface. The relationship between the geometric shape of the scintillation crystal and the light collection efficiency is as Figure 2 shown.

[0025] The simulation results show that the light collection efficiency is the highest when the crystal shape is a frustum of a cone (when the inclination angles of the frustum of a cone are 85°, 80°, 75°, 70°, and 65°, the light collection efficiencies are 70.64%, 73.2%, 77.20%, 80.31%, and 81.49% respectively). Followed by the cube (67.67%), cylinder (67.22%), and cuboid (65.28%). The light output has been improved to varying degrees. Considering the detection efficiency factor comprehensively, the frustum of a cone with an angle of 85° is taken as the optimized structure, and the light output can reach about 70.64%. The ratio of the light collection efficiency of the cylinder to that of the 85° frustum of a cone is about 105.09% of that of the cylinder.

[0026] Secondly, the light collection uniformity was studied for various crystal shapes, and the light collection uniformity simulation was further carried out to optimize the crystal shape. The diagonal axis of the largest cross-section of the crystal was selected. After photons were emitted at different positions in the scintillator, the change in the number of full-energy peak photons of the crystal at different positions was obtained. Figure 3 Shows the change in light collection uniformity after photons are emitted at different positions in the scintillator. The light output non-uniformity is defined by the following formula (2) as:

[0027] U = MAX photoncollection - MIN photoncollection (2)

[0028] The simulation results are as Figure 3 shown. It can be seen that the contribution of the 85° frustum of a cone to the uniformity is 3.75%, the contribution of the cylinder to the uniformity is 4.51%, the contribution of the cube to the uniformity is 4.90%, and the contribution of the cuboid to the uniformity is 5.20%. The shape with the best light collection uniformity is the frustum of a cone, followed by the cylinder, cube, and cuboid. The crystal shape has a certain impact on the light collection uniformity. Therefore, improving the light collection uniformity through the shape is also a way to optimize the detector design and can improve the energy resolution of the detector.

[0029] Finally, the influence of the single-sided and double-sided readout methods of the detector on the photon collection efficiency was studied, and the test results are as Figure 4 shown in Table 1.

[0030] Table 1 Number of photons, photon collection efficiency, relative photon collection efficiency of double-sided readout, and percentage increase relative to single-sided readout for different shapes of single-sided and double-sided

[0031]

[0032] The method of dual-ended photon output is adopted to reduce the path of photons during propagation in the scintillator crystal, so as to achieve the purpose of increasing the photon collection efficiency. Figure 4 Taking the maximum value as the standard, the relative light collection efficiency data of single-sided and double-sided readouts of different shapes are obtained, and the light collection efficiency of various readout methods can be clearly seen. In all cases, the light collection efficiency of double-sided readout is higher than that of single-sided readout. It can be found from Table 1 that compared with the single-sided readout method, the use of double-sided readout can enhance by 10 - 20%. However, when using double-sided readout, the change of the light collection efficiency of each shape is not obvious, and the influence of the shape on the light collection is very small.

[0033] In order to verify the optical model, an experimental platform was built to conduct light collection simulation verification for different shapes and single-sided and double-sided readout methods. At present, the cost of lanthanum bromide crystals is expensive, and too many crystals with various shapes and surface treatments are required for the experiment. Therefore, the CsI:Na scintillation crystal produced by Beijing Hamamatsu Photonics was used in the experiment. The reflection film wrapped on the crystal is a Teflon film. The silicone oil is used for coupling between the light-emitting surface of the scintillator and the PMT. The light-emitting surface is polished. The 137Cs source is used for crystal excitation, and the radiation source is located directly above the crystal. The photomultiplier tube (Hainan Zhanchuang XP5382) receives the optical signal to generate an electrical signal. After the output signal passes through the fan-in and fan-out, it finally reaches the data acquisition plug-in (CAEN DT5751) to directly output the waveform signal. The experiment covers four shapes of crystals: cylinder, cube, cuboid, and 85° frustum. At the same time, a control experiment of single-sided and double-sided readout was also carried out, and the results are as Figure 5 and Figure 6 shown.

[0034] Figure 5 shows the comparison results of the double-sided readout experiment of the scintillator and Geant4 under different shapes, which are normalized with the maximum value. Figure 6 shows the comparison results of the experiment of the increase of the double-sided readout of the scintillator detector relative to the single-sided readout and Geant4.

[0035] The comparison results between the experimental data and the MC simulation data show that there is good consistency between the two, with the difference being less than ±2%. The order of the light collection efficiency from high to low is frustum, cube, cylinder, and cuboid, and the order of the two is also consistent. This fully demonstrates the rationality and reliability of the set of simulation parameters given in this paper. When changing the material optical parameters and shape of the scintillator, the simulation program can obtain results close to the real situation.

[0036] Taking into account factors such as photon collection efficiency, the various shapes of the crystal on light collection uniformity, detector volume, and detection efficiency, the present invention proposes that the photon collection system adopts the SIPM mode with high gain, high sensitivity, low bias voltage, insensitivity to magnetic fields, and compact structure, and the dual-end output mode. For the detector of LaBr3(Ce) scintillation crystal, a 3-inch 85° frustum LaBr3(Ce) crystal is used. The photon collection efficiency is about 79.58%, and the photon collection efficiency is increased by about 18.39% compared with the traditional single-end output mode of the cylinder, and the light collection uniformity is increased from 4.51% to 3.75%.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A scintillator detector, characterized in that, It includes a first photomultiplier tube, a second photomultiplier tube, a scintillating crystal, a first signal processing circuit, a second signal processing circuit, and a pulse signal addition circuit; the shape of the scintillating crystal is a frustum of a cone with an included angle of 85° between the side surface and the bottom surface, the first photomultiplier tube and the second photomultiplier tube are respectively coupled to the top surface and the bottom surface of the scintillating crystal, the first signal processing circuit is electrically connected to the first photomultiplier tube, the second signal processing circuit is electrically connected to the second photomultiplier tube, and the pulse signal addition circuit is respectively electrically connected to the first signal processing circuit and the second signal processing circuit.

2. The scintillator detector according to claim 1, wherein: Both the first photomultiplier tube and the second photomultiplier tube are silicon photomultiplier tubes.

3. The scintillator detector according to claim 1 or 2, characterized in that: The scintillating crystal is a cerium-doped lanthanum bromide crystal.

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