A time-of-flight detector based on Cherenkov radiation detection and its fabrication method

Abstract

This invention discloses a time-of-flight detector based on Cherenkov radiation detection and its fabrication method. The detector includes a Cherenkov radiator, with a photocathode coated on the light-emitting surface of the radiator, and an anode array-type photoconverter located behind the photocathode. The Cherenkov radiator is a two-dimensional array structure, wherein low-refractive-index transparent optical material layers are respectively disposed on the opposite sides of adjacent array units, and high-reflectivity material is filled between the low-reflectivity transparent optical material layers. One end of the two-dimensional array structure is the incident light surface, and the other end is the light-emitting light surface. The Cherenkov radiator interacts with the incident radiation to generate Cherenkov photons and confines them in the corresponding array units for transmission to the photocathode. The photocathode converts the input Cherenkov light into photoelectrons and inputs them to the anode array-type photoconverter. The anode array-type photoconverter amplifies the input photoelectrons and outputs them. This invention improves the number of detected photons and the position resolution capability.

Description

Technical Field

[0001] This invention belongs to the field of nuclear radiation detection and nuclear technology applications, and in particular relates to an array-type time-of-flight detector based on Cherenkov radiators and its manufacturing method. Background Technology

[0002] In the field of nuclear radiation detection, detectors, as the first step in detecting particles, are the foundation for all subsequent nuclear technologies and nuclear analysis applications. Combining different particle detection materials and detector types allows for applications in various scenarios. A commonly used detector type is a scintillator combined with a silicon photomultiplier tube (SiPM) or photomultiplier tube (PMT) to detect radiation. An important application is time-of-flight (TOF) measurement. TOF technology uses the scintillation signal generated by a pair of annihilated photons within a scintillator for time discrimination, accurately measuring the time difference between the arrival of the two annihilated photons at the detector. It plays a crucial role in nuclear radiation detection and nuclear technology applications. For example, the addition of TOF technology significantly improves positron emission tomography (PET) imaging in nuclear medicine, significantly increasing the signal-to-noise ratio of PET images and bringing important improvements to clinical applications. However, due to the limitations of the scintillator's own emission mechanism and the single-photon time resolution of SiPM and PMT, the time resolution of this detector scheme is nearing its limit, making significant improvements difficult.

[0003] In transient photon detection, when annihilated photons are deposited in a scintillator, several high-energy electrons are generated and move at superluminal speeds for a short period, producing Cherenkov light. The generation of Cherenkov light is almost synchronous with the deposition of annihilated photons. Utilizing this transient characteristic, increasing the Cherenkov photon output yield could potentially significantly improve the detector's temporal resolution. Regarding single-photon time resolution (SPTR) in photodetectors, the SPTR of various SiPM devices currently documented in the literature remains around 100 ps, ​​and due to factors such as silicon ionization, it is difficult to significantly improve the SPTR performance of SiPM devices.

[0004] Microchannel plate photomultiplier tubes (MCP-PMTs) are a new type of photodetector device. They are PMT devices that use microchannel plates (MCPs) instead of traditional daradox structures to achieve electron multiplication. Generally, sub-millimeter thick MCPs can achieve 10-1 electron multiplication. 4 Electron multiplication on both sides can be achieved by stacking two MCPs to reach 10. 7Horizontal electron multiplication can be used in various low-light detection applications. PMTs used in fast time-resolution applications are typically near-field focusing MCP-PMTs, consisting of four parts: an optical window, a photocathode, a microchannel plate, and an anode. The optical window is usually made of quartz or lead glass. Photons pass through the optical window and strike the photocathode for photoelectric conversion. The time it takes for photoelectrons to travel from the photocathode to the microchannel plate is extremely short. The photoelectrons are multiplied and amplified within the MCP channels. MCPs have a natural advantage of fast response; therefore, this type of MCP has an ultrafast response time. Its time-resolution capability can be optimized by changing the aperture size, channel length, and coating method of the MCP.

[0005] Compared to traditional darad photomultiplier tubes, MCP-PMTs exhibit superior single-photon time resolution due to the thinner MCP, faster time response, and significantly shorter electron travel distance in a vacuum. These excellent position resolution, time resolution, and magnetic field resistance properties make MCP-PMTs promising candidates for application in detector systems for nuclear radiation detection and other nuclear technology applications.

[0006] The relationship between the number of photoelectrons on the photocathode in photoelectric conversion devices is as follows:

[0007] n∝LTE*W ab *QE*N

[0008] Wherein, LTE is a coefficient related to total internal reflection caused by photons traveling from an optically denser medium to an optically less dense medium, and is affected by the refractive index of the medium, W ab QE is the coefficient related to the absorption of photons by the optical window of the optoelectronic device, QE is the quantum efficiency of the conversion of photons reaching the photocathode into photoelectrons, and N is the number of photons generated in the radiating body.

[0009] Taking yttrium lutetium silicate scintillation crystal (LYSO) as an example (scintillation yield approximately 30,000 photons / MeV), estimate the number of photoelectrons n reaching the optoelectronic device and undergoing photoelectric conversion under conventional detector structure under 511keV gamma ray irradiation. s :

[0010] n s ≈30000 × 0.511 × 0.6 × 0.9 × 30% = 2483 photons

[0011] Taking lead fluoride as an example (Cherenkov photon yield is approximately 29 photons / 511keV), the estimated number of photoelectrons n reaching the optoelectronic device and undergoing photoelectric conversion under 511keV gamma ray irradiation in a conventional detector structure is as follows: c :

[0012] n c ≈29×0.58×0.9×30%≈4 photons

[0013] The comparison shows that the output of Cherenkov light is 10 times smaller than that of scintillation light. 2 -10 3 When Cherenkov light undergoes light loss during transmission, including total internal reflection and self-absorption, it can only be converted into a few photoelectrons at the photocathode of an optoelectronic device. This reduction in photon count affects the fast-time performance of Cherenkov radiation. A qualitative change in photon count requires new structures that break with tradition.

[0014] Traditional scintillator detectors are suitable for scintillator materials with high light yield, where photon loss during transmission has little impact on subsequent analysis. However, for Cherenkov photons, which have inherently low light yield, ensuring that as many photons as possible are detected is fundamental. The ultimate goal is to maintain good position resolution in a multi-anode structure while ensuring a sufficient number of photons.

[0015] If a detector scheme consisting of a scintillator, optical adhesive, and optoelectronic devices, i.e., the traditional TOF-PET detector scheme mentioned above, is used to detect Cherenkov photons, a large amount of scintillating light will become noise in the detection of Cherenkov photons, affecting the timing performance. At the same time, the traditional detector structure means that photons will inevitably be transmitted from an optically denser medium to an optically less dense medium, which will result in total internal reflection, causing a large loss of photons during transmission and thus reducing the timing performance and position resolution.

[0016] Most existing literature on Cherenkov photon detection employs traditional detector structures. Detector structures based on Cherenkov radiators integrated with MCP-PMTs typically require the stable deposition of the Cherenkov radiator on the photocathode of the MCP-PMT, followed by amplification and multiplication of photoelectrons using a single or multiple MCPs, and finally signal readout through the anode. R. Ota et al. were the first to propose this design for Cherenkov photon detection. Their design uses a layer of aluminum oxide (Al₂O₃) coated onto lead glass to prevent lead displacement from the glass, which would darken the entire front-end Cherenkov radiator's transparent portion. This creates a single-pixel integrated MCP-PMT, and imaging is achieved using a point-scanning method with this structure. Similar to this design, D. Yvon et al. proposed replacing the lead glass with lead tungstate (PbWO₄) to utilize the small number of fast scintillation photons generated by PbWO₄ and proposed the idea of ​​using continuous Cherenkov radiators for DOI (Depth of Indication). Overall, while current integrated MCP-PMTs have designs for multi-anode structures, their position resolution is poor, and they cannot effectively utilize Cherenkov photons. The improvement needed is to enhance position resolution while improving light collection, thus achieving position-sensitive photoelectric conversion devices. Summary of the Invention

[0017] To address the problems existing in current integrated detector designs, this invention aims to provide a Cherenkov radiator-based array-type time-of-flight detector design. This invention combines the advantages of Cherenkov radiation's time performance with the advantages of arrays in improving position resolution, designing an array-type time-of-flight detector based on Cherenkov radiators. This provides a new technical means for Cherenkov photon detection, improving position resolution while increasing the number of detected photons.

[0018] The technical solution of this invention is as follows:

[0019] A time-of-flight detector based on Cherenkov radiation detection is characterized by comprising a Cherenkov radiator, wherein the light-emitting surface of the Cherenkov radiator is coated with a photocathode, and an anode array-type photoelectric converter is disposed behind the photocathode; the Cherenkov radiator is a two-dimensional array structure, wherein low-refractive-index transparent optical material layers are respectively disposed on the opposite sides of two adjacent array units, and high-reflectivity material is filled between the low-reflectivity transparent optical material layers; one end of the two-dimensional array structure is the light-incident surface, and the other end is the light-emitting surface;

[0020] The Cherenkov radiator is used to interact with the incident rays to generate Cherenkov photons and confine them in the corresponding array unit for transmission to the photocathode;

[0021] The photocathode is used to convert the input Cherenkov light into photoelectrons and input them into the anode array type photoelectric converter;

[0022] The anode array type photoelectric converter is used to amplify the input photoelectrons and output them.

[0023] Furthermore, the Cherenkov radiator is cut to obtain the two-dimensional array structure; wherein the outer sides of the array units on the four sides of the two-dimensional array structure are not cut through or have a certain thickness.

[0024] Furthermore, the Cherenkov radiator is cut, but the light-emitting surface is not cut through, to obtain the two-dimensional array structure in which each array unit is connected and fixed on the light-emitting surface.

[0025] Furthermore, the thickness of the uncut surface is x mm.

[0026] Furthermore, the surface of the cut Cherenkov radiator is polished.

[0027] Furthermore, the two-dimensional array structure consists of n×n array elements, each array element having an end face size of d×dmm. 2 The thickness of the Cherenkov radiator is h mm, where n, d, and h are natural numbers and their specific values ​​are not specifically limited.

[0028] Furthermore, the anode array type photoelectric converter is a microchannel plate photomultiplier tube.

[0029] A method for fabricating a time-of-flight detector based on Cherenkov radiation detection, comprising the following steps:

[0030] 1) Cut the selected Cherenkov radiator into a two-dimensional array structure; set low-refractive-index transparent optical material layers on the opposite sides of two adjacent array units, and then fill the space between the low-reflection transparent optical material layers with high-reflection material. One end of the two-dimensional array structure is the light-incident surface and the other end is the light-exit surface.

[0031] 2) A photocathode is coated on the light-emitting surface;

[0032] 3) Integrate the Cherenkov radiator coated with the photocathode onto the anode array type photoconverter, wherein the photocathode is opposite to the anode array type photoconverter and is used to input the output photoelectrons into the anode array type photoconverter.

[0033] This invention relates to a time-of-flight detector based on Cherenkov radiation detection. It uses a Cherenkov radiator as both the material generating Cherenkov radiation and the medium for transmitting optical photons. During photon transmission, photons are confined to the generated region and prevented from diffusing to other areas. Ultimately, this achieves an integrated time-of-flight detector combining a Cherenkov radiator, photocathode, multiplication stage, and array anode. The specific implementation steps of the design scheme are as follows:

[0034] Based on the effective atomic number, refractive index, spectral response range, and other properties of Cherenkov radiators, the required Cherenkov radiators are selected according to the detection wavelength. After a cutting process, the Cherenkov radiator is as follows... Figure 1 , Figure 2 As shown, the cut radiator is a two-dimensional array structure, in which the outer side of the array unit located on the four sides can be cut through or left with a certain thickness. After cutting, the surface of the radiator is polished.

[0035] After cutting the prepared Cherenkov radiator, a low-refractive-index transparent optical material is first attached to the radiator surface within the gap. Then, a high-reflectivity material is filled between adjacent layers of low-refractive-index transparent optical material, and a sealing treatment is performed. Figure 3 .

[0036] A photocathode with high sensitivity to ultraviolet light is coated onto the treated Cherenkov radiator, such as... Figure 4 As shown.

[0037] The detector is fabricated by integrating the processed photocathode and Cherenkov radiator onto an anode array-type photoelectric conversion device. Figure 5 As shown.

[0038] As an improvement to the aforementioned device, without limitation, the selected Cherenkov radiator does not produce scintillation under gamma ray irradiation.

[0039] As an improvement to the above device, the radiator is cut into n×n array units, and the end face size of each array unit is d×d mm. 2 The overall thickness of the Cherenkov radiator is h mm. Where n, d, and h are natural numbers, and their specific values ​​are not specifically restricted.

[0040] As an improvement to the aforementioned device, and without limitation, the size of each radiator strip after the Cherenkov radiator is cut is d×d×h mm. 3 And leave a section at the bottom with a thickness of x mm that is not cut, for the stability of the overall mechanical structure, such as... Figure 6 As shown.

[0041] The uncut portion with a thickness of x mm is left, where the specific value of x is to ensure that photons generated in a certain area (radiator strip) will not diffuse to other areas through other light propagation media.

[0042] As an improvement to the aforementioned device, without limitation, a photocathode sensitive to wavelengths in the range of 180nm-600nm and with an average quantum efficiency of 15% or higher is deposited on the photon emitting surface of the treated Cherenkov radiator.

[0043] As an improvement to the above-mentioned device, and without limitation, the photoelectric conversion device is a microchannel plate photomultiplier tube.

[0044] The advantages of this invention are as follows:

[0045] Compared to detectors that separate the luminescent material from the array-type photoelectric conversion device, this invention maximizes the retention of generated photons, thereby improving detection efficiency and achieving position resolution. This invention can: 1) minimize optical crosstalk between different regions caused by the presence of the medium during photon propagation. Figure 7 ,like Figure 8 As shown; that is, if the radiator of the two-dimensional array structure in this invention is directly combined with the detector with the optical window, crosstalk will occur, such as Figure 7 ; and adopt Figure 8 The structure shown can avoid crosstalk; 2) It simplifies the structure of the detector using an array-type photoelectric conversion device, avoiding light loss during light propagation in the medium. The influence of the number of photoelectrons on the photocathode in the photoelectric conversion device is as follows:

[0046] n∝LTE*W ab *QE*N

[0047] Wherein, LTE is a constant related to total internal reflection caused by photons traveling from an optically denser medium to an optically less dense medium, and is affected by the refractive index of the medium, W ab Let QE be a constant related to photon absorption by the optical window of the optoelectronic device, QE be the quantum efficiency of photon conversion to photoelectron at the photocathode, and N be the number of photons generated in the radiating body. This invention can eliminate parameters LTE and W. ab Impact:

[0048] n∝QE*N

[0049] 3) Since the beam splitting caused by the presence of the optical transmission medium is avoided, the position resolution of the array detector can be improved.

[0050] The method of this invention provides a supplement and an innovation in array-type detector structure design for the fields of nuclear radiation detection and nuclear technology applications, which is conducive to subsequent analysis and research of Cherenkov photons and is suitable for application and promotion in nuclear medicine imaging equipment. Attached Figure Description

[0051] Figure 1 This is a partially pixelated side view.

[0052] Figure 2 This is a pixelated top view.

[0053] Figure 3 A schematic diagram illustrating the process of injecting low-refractive-index optical adhesive and high-reflectivity material and then sealing it.

[0054] Figure 4 This is a schematic diagram of the photocathode coating.

[0055] Figure 5 This is the first integrated detector of the present invention.

[0056] Figure 6 This is the second integrated detector of the present invention.

[0057] Figure 7 This represents the process of photons propagating in a detector separated from the Cherenkov radiator and the array-type photoelectric conversion device (dashed lines represent photons that diffuse into other regions).

[0058] Figure 8 This describes the process of photons propagating in a detector that integrates a Cherenkov radiator and an array-type photoelectric conversion device. Detailed Implementation

[0059] The present invention will be described in detail below with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention. Any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0060] This invention proposes a time-of-flight detector based on Cherenkov radiation detection, and the specific implementation steps are as follows:

[0061] (1) Based on the effective atomic number, refractive index, spectral range, and other properties of the Cherenkov radiator, the desired Cherenkov radiator is selected, such as lead fluoride (PbF2), lead tungstate (PbWO4), lead glass, etc., and the appropriate material is selected according to the detector design and requirements. Specifically, the method for selecting Cherenkov radiators is known to those skilled in the art and will not be elaborated here.

[0062] (2) The Cherenkov radiator undergoes complete penetrating cutting and polishing of all six sides, as shown in the image. Figures 1-2 And then perform surface polishing.

[0063] The cutting can be performed using the most common cutting methods to cut out the target number of units and the array structure.

[0064] As an improvement to step (2), without limitation, the size of each radiator strip after the Cherenkov radiator is cut is 3×3×5mm. 3 Cut out 8×8 areas and leave 0.1mm to 3mm uncut at the bottom for overall mechanical structure stability.

[0065] In step (2), the specific method of creating an array by cutting the radiator is known to those skilled in the art and will not be elaborated here. It should also be noted that in practical use, the detector's positional resolution is affected by the remaining cut thickness of the Cherenkov radiator and the size of the cut area.

[0066] (3) After cutting the prepared Cherenkov radiator, a low-refractive-index transparent material is placed in the gap, followed by a high-reflectivity material, and finally sealed. Figure 3 .

[0067] In step (3), it should be noted that the use of low-refractive-index and high-reflectivity materials is to prevent photons from diffusing into adjacent radiator strips. Sealing is necessary for mechanical structural stability and for subsequent photocathode plating.

[0068] In step (3), the specific selection of low-refractive-index transparent materials and high-reflectivity materials is known to those skilled in the art and will not be repeated here.

[0069] (4) A photocathode with an average sensitivity greater than 15% to the ultraviolet wavelength range of 180nm-600nm is deposited on the treated Cherenkov radiator, such as... Figure 4 It should be noted that a photocathode with high sensitivity to ultraviolet light was chosen because the Cherenkov photon distribution is inversely proportional to the wavelength.

[0070]

[0071] Where N is the number of photons with wavelengths between λ1 and λ2 radiated per unit length of Cherenkov radiator, z is the charge of the charged particle, and θ is the Cherenkov radiation angle.

[0072] (5) Finally, the detector fabrication is completed by integrating the processed photocathode and Cherenkov radiator onto the anode array type MCP-PMT. Figure 5 Specifically, the integration design of the MCP and anode can be carried out in accordance with the industry's traditional methods, which are known to those skilled in the art and will not be elaborated here.

[0073] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A time-of-flight detector based on Cherenkov radiation detection, characterized in that, The device includes a Cherenkov radiator, wherein the light-emitting surface of the Cherenkov radiator is coated with a photocathode, and an anode array type photoelectric converter is provided behind the photocathode; the Cherenkov radiator is a two-dimensional array structure, wherein low-refractive-index transparent optical material layers are respectively disposed on the opposite sides of two adjacent array units, and high-reflectivity material is filled between the low-reflectivity transparent optical material layers; one end of the two-dimensional array structure is the light-incident surface, and the other end is the light-emitting surface; The Cherenkov radiator is cut, but the light-emitting surface is not cut through, to obtain the two-dimensional array structure in which each array unit is connected and fixed on the light-emitting surface. The Cherenkov radiator is used to interact with the incident rays to generate Cherenkov photons and confine them in the corresponding array unit for transmission to the photocathode; The photocathode is used to convert the input Cherenkov light into photoelectrons and input them into the anode array type photoelectric converter; The anode array type photoelectric converter is used to amplify the input photoelectrons and output them.

2. The time-of-flight detector according to claim 1, characterized in that, The two-dimensional array structure is obtained by cutting the Cherenkov radiator; wherein the outer sides of the array units on the four sides of the two-dimensional array structure are not cut through or have a certain thickness.

3. The time-of-flight detector according to claim 1, characterized in that, The thickness of the uncut surface is x mm.

4. The time-of-flight detector according to claim 2 or 3, characterized in that, The surface of the cut Cherenkov radiator is polished.

5. The time-of-flight detector according to claim 1, characterized in that, The two-dimensional array structure consists of n×n array elements, with each array element having an end face size of d×d mm. 2 The thickness of the Cherenkov radiator is h mm.

6. The time-of-flight detector according to claim 1, characterized in that, The anode array type photoelectric converter is a microchannel plate photomultiplier tube.

7. A method for fabricating a time-of-flight detector based on Cherenkov radiation detection, comprising the following steps: 1) Cut the selected Cherenkov radiator into a two-dimensional array structure; Low-refractive-index transparent optical material layers are respectively set on the opposite sides of two adjacent array units, and then high-reflectivity material is filled between the low-reflectivity transparent optical material layers. One end of the two-dimensional array structure is the light-incident surface and the other end is the light-exit surface. The Cherenkov radiator is cut without cutting through the light-emitting surface, resulting in the two-dimensional array structure in which each array unit is connected and fixed on the light-emitting surface. 2) A photocathode is coated on the light-emitting surface; 3) Integrate the Cherenkov radiator coated with the photocathode onto the anode array type photoconverter, wherein the photocathode is opposite to the anode array type photoconverter and is used to input the output photoelectrons into the anode array type photoconverter.

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