CN108663705B - Cladding method of composite crystal and composite crystal detector - Google Patents
Cladding method of composite crystal and composite crystal detector Download PDFInfo
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Abstract
The application discloses a cladding method of a composite crystal and a composite crystal detector, wherein the cladding method comprises the following steps: grinding and polishing the surfaces of the NaI (Tl) crystal and the CsI (Na) crystal to ensure that the NaI (Tl) crystal and the CsI (Na) crystal are clean and bright; aligning NaI (Tl) crystal, CsI (Na) crystal and quartz glass from top to bottom, sequentially stacking, and bonding into a whole through transparent organic silicon gel; after the glue is cured, adhering the first reflecting film on the side and bottom surfaces of the CsI (Na) crystal through a transparent organic silicon gel; polishing the edge of the top surface of the NaI (Tl) crystal to form an annular diffuse reflection area; covering a second reflecting film on the top surface of the NaI (Tl) crystal, covering a third reflecting film on the surface of the second reflecting film, bending the third reflecting film to the side surface of the NaI (Tl) crystal along the edge of the top surface of the NaI (Tl) crystal, and coating the first reflecting film connected with the side surface of the CsI (Na) crystal. The coating method provided by the invention has simple process, does not need chamfering treatment, and avoids the risk of crystal breakage; the formed composite crystal detector has good energy resolution.
Description
Technical Field
The disclosure relates to the field of high-energy X/gamma ray detection, in particular to a composite crystal, a coating method for the composite crystal and a composite crystal detector.
Background
In the field of radiation detection, sodium iodide (thallium-activated) single crystals (i.e., nai (tl) crystals) and cesium iodide (thallium-activated) single crystals (i.e., csi (na) crystals) are the two most widely used inorganic scintillation crystals. As shown in table 1, they have a very high fluorescence output capability; the maximum emission wavelength is close to the response peak wavelength (about 400nm) of a photomultiplier tube (PMT) (of the double-alkaline photocathode material with the current optimal quantum conversion efficiency), and the maximum emission wavelength and the response peak wavelength can be well matched to realize the highest light output efficiency, so that high energy resolution is obtained; can form a single crystal or polycrystal form, and can be made into various geometric shapes, and the use is convenient; has higher material density and high detection efficiency on X/gamma rays. Based on the advantages, the method has wide application in astronomical observation, medical imaging, customs security inspection and the like.
TABLE 1 Properties of commonly used inorganic scintillation crystals
Because the maximum emission wavelengths of the NaI (Tl) crystal and the CsI (Na) crystal are close, the NaI (Tl) crystal and the CsI (Na) crystal are usually optically coupled to form a composite crystal, and the composite crystal is read by the same PMT to form a composite crystal detector. The NaI (Tl) crystal is used as a main crystal and is used for detecting X/gamma rays and acquiring information such as energy, flow intensity and the like; the CsI (Na) crystal is used as a secondary crystal, detects higher-energy X/gamma rays incident from the front side of the NaI (Tl) crystal, Compton scattering from the NaI (Tl) crystal and X/gamma rays from the back side of the NaI (Tl) crystal, and also plays a light guide role. By utilizing the difference of luminescence decay time of the NaI (Tl) crystal and the CsI (Na) crystal (the former is about 250ns and the latter is about 630ns at room temperature), output signals of the two crystals can be discriminated by a pulse waveform discriminator, so that extraction of NaI (Tl) effective signals and shielding of CsI (Na) background signals are realized. Therefore, the NaI (Tl)/CsI (Na) composite crystal detector is a high-performance X/gamma ray detector with simple structure and passive shielding and forward (2 pi solid angle) collimation function. This advantage makes it widely used in astronomical observations such as BepposAx/PDS (Italy, 1996 + 2002), HEXTE (USA, 1996 + 2012), HXMT/HED to be emitted at 2017, etc.
The NaI (Tl)/CsI (Na) composite crystal is the most core part of the detector and is responsible for converting X/gamma rays into fluorescence, so that the maximization of the fluorescence output of the composite crystal and the response consistency of all areas of the main crystal are key points for ensuring the optimal performance of the detector, and the aim of coating the composite crystal is achieved.
For conventional cylindrical composite crystals with diameters less than 5 inches, full coverage can be achieved with commercially available PMTs (e.g., 5 inch flat end PMT R877 from Hamamatsu, japan) which typically use a surface finish in combination with a reflective film coating. For a large-area composite crystal with the size of more than 5 inches, due to the size limitation of a plane end window type PMT, the output end face of the crystal cannot be completely covered, and (if the crystal is coated according to a conventional method), fluorescence generated in the crystal has a reflection and absorption condition in a non-PMT corresponding area of the output end face, so that the read fluorescence intensity of the PMT is lower than the originally generated fluorescence intensity, and in addition, the edge effect is added, so that the overall performance of the composite crystal is remarkably reduced. The crystal usually needs special treatment, such as NaI (Tl)/CsI (Na) composite crystal in a hard X-ray detector on HEXTE satellite, adopting a method of chamfering an output end face and matching with polishing the surface of the crystal and coating a reflecting film; similar methods have been used for PDS detectors on the BeppoSAX satellites. This method requires chamfering of CsI (Na) crystals as light guides by mechanical processing, which involves the risk of crystal breakage; in addition, because only loose adhesion relationship exists between the reflective film and the crystal, and the reflective film itself cannot be glued, there is no connection relationship between the side surface of the crystal and the sealing box (the metal shell for placing the composite crystal and preventing the crystal from deliquescing), which is not favorable for damping design.
Disclosure of Invention
The present invention has been made in view of the above-mentioned drawbacks or disadvantages of the prior art.
In a first aspect, the present invention provides a method for coating a composite crystal, comprising the steps of:
s101: grinding and polishing the surfaces of NaI (Tl) crystals and CsI (Na) crystals to ensure that the NaI (Tl) crystals and the CsI (Na) crystals are clean and bright;
s102: aligning the NaI (Tl) crystal, the CsI (Na) crystal and quartz glass from top to bottom, sequentially stacking the NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass, and bonding the NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass into a whole through transparent organic silicon gel;
s103: after the glue is cured, adhering a first reflecting film on the side and bottom surfaces of the CsI (Na) crystal through a transparent organic silicon gel;
s104: polishing the edge of the top surface of the NaI (Tl) crystal to form an annular diffuse reflection area;
s105: covering a second reflecting film on the top surface of the NaI (Tl) crystal, covering a third reflecting film on the surface of the second reflecting film, bending the third reflecting film to the side surface of the NaI (Tl) crystal along the edge of the top surface of the NaI (Tl) crystal and covering the first reflecting film connected with the CsI (Na) crystal side surface.
In a second aspect, the invention provides a composite crystal detector, which comprises a composite crystal prepared by the coating method, wherein the composite crystal comprises a NaI (Tl) crystal, a CsI (Na) crystal and quartz glass which are sequentially stacked from top to bottom, and the quartz glass of the NaI (Tl)/CsI (Na) composite crystal is coupled with a photomultiplier through a light coupling agent; wherein
The NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass are all cylindrical structures, the NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass are aligned in position and are connected through transparent organic silicon gel in an adhesive mode, and an annular diffuse reflection area is arranged at the edge of the top face of the NaI (Tl) crystal; first reflecting films are arranged on the side surfaces and the bottom surface of the CsI (Na) crystal, and the first reflecting films cover the side surfaces and the bottom surface of the CsI (Na) crystal and only expose the side surfaces and the bottom surface of the quartz glass; the top surface of the NaI (Tl) crystal is covered with a second reflection film, the surface of the second reflection film is provided with a third reflection film, and the third reflection film is bent from the top surface edge of the NaI (Tl) crystal to wrap the side surface of the NaI (Tl) crystal.
Compared with the prior art, the invention has the beneficial effects that:
the cladding method of the composite crystal has certain universality, is more suitable for large-area crystals (the diameter of the crystal is more than 5 inches, for example, the diameter of the NaI (Tl) crystal and the diameter of the CsI (Na) crystal are both more than 5 inches in the application), and realizes the adjustment of a fluorescence light path generated in the central area of the NaI (Tl) crystal by arranging the annular diffuse reflection area at the edge of the top surface of the NaI (Tl) crystal, so that the response of each area of the large-area crystal to incident photons has good consistency, and the large-area crystal has good energy resolution; the composite crystal detector is simple to operate and easy to realize, chamfering treatment on the CsI (Na) crystal is not needed, the risk of crystal breakage is avoided, the composite crystal provided by the application has excellent performance, and meanwhile, the performance of the composite crystal detector is improved.
Drawings
Other features, objects and advantages of the present application will become more apparent upon reading of the following detailed description of non-limiting embodiments thereof, made with reference to the accompanying drawings in which:
FIG. 1 is a block flow diagram of a method for coating a composite crystal according to the present invention;
FIG. 2 is a schematic structural diagram of a composite crystal provided by the present invention;
FIG. 3 is an enlarged view of a portion I of FIG. 2;
FIG. 4 is a schematic top view of a NaI (Tl) crystal in a composite crystal provided by the present invention;
FIG. 5 is a schematic diagram of the fluorescence output path in the composite crystal provided by the present invention;
FIG. 6 is a schematic structural diagram of a composite crystal detector provided by the present invention;
FIG. 7 is a block diagram of a composite crystal performance testing system provided by the present invention;
FIG. 8 is a graph of a test area distribution sampled over the surface of a composite crystal;
FIG. 9 is an Am-241 energy spectrum of the local position output of NaI (Tl) crystal;
FIG. 10 is a schematic illustration of the peak position of a 59.5keV gamma ray energy spectrum for a localized region;
FIG. 11 is a schematic illustration of the spectral resolution of 59.5keV gamma rays at a localized area;
FIG. 12 is the Am-241 total energy spectrum and the fitting result after the 27 regions in FIG. 8 are overlapped.
Detailed Description
The present application will be described in further detail with reference to the following drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant invention and not restrictive of the invention. It should be noted that, for convenience of description, only the portions related to the present invention are shown in the drawings.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.
FIG. 1 is a schematic view of a method for coating a composite crystal according to the present invention. Fig. 2 is a schematic structural diagram of the composite crystal provided by the present invention. As shown in fig. 1 and 2, the present invention provides a method for coating a composite crystal, comprising:
step S101: grinding and polishing the surfaces of the NaI (Tl) crystal 1 and the CsI (Na) crystal 2 to ensure that the NaI (Tl) crystal 1 and the CsI (Na) crystal 2 are clean and transparent;
step S102: aligning NaI (Tl) crystal 1, CsI (Na) crystal 2 and quartz glass 3 from top to bottom, sequentially stacking, and bonding into a whole through transparent organic silicon gel;
step S103: after the glue is cured, the first reflection film 4 is glued on the side and bottom surfaces of the CsI (Na) crystal 2 through a transparent organic silicon gel;
step S104: polishing the edge of the top surface of the NaI (Tl) crystal 1 to form an annular diffuse reflection area 7;
step S105: covering a second reflecting film 5 on the top surface of the NaI (Tl) crystal 1, covering a third reflecting film 6 on the surface of the second reflecting film 5, bending the third reflecting film 6 to the side surface of the NaI (Tl) crystal 1 along the edge of the top surface of the NaI (Tl) crystal 1 and coating a first reflecting film 4 connected with the side surface of the CsI (Na) crystal 2. Finally, a composite crystal as shown in fig. 2 is formed.
Wherein, the edge of the top surface of the NaI (Tl) crystal 1 is an annular diffuse reflection area 7, and the other parts of the NaI (Tl) crystal 1 and the CsI (Na) crystal 2 are both mirror reflection areas.
Further, a third reflective film 6 is attached to the surface of the second reflective film 5 and the second reflective film 5 is pressed on the top surface of the nai (tl) crystal 1.
Further, the first reflective film 4 and the second reflective film 5 are ESR reflective films, and the ESR reflective films are enhanced specular reflective films, and are used for reflecting and collecting fluorescence; the third reflective film 6 is a Teflon reflective film (i.e. Teflon reflective film), which utilizes the soft film property of the Teflon reflective film to press the second reflective film 5 (i.e. ESR reflective film) on the top surface of the nai (ti) crystal, and reflects and collects the fluorescence.
Further, the positional alignment includes: central axes of the NaI (Tl) crystal 1, the CsI (Na) crystal 2 and the quartz glass 3 are superposed to ensure that the fluorescence output from the composite crystal is collected with high efficiency and high reliability.
Further, in the central axis direction of the composite crystal, the top surface of the NaI (Tl) crystal comprises a first part facing the quartz glass and a second part outside the first part, and in order to ensure the rapid propagation of the fluorescence light path and the effective collection of the fluorescence, the width of the annular diffuse reflection area does not exceed the width of the second part.
Further, the NaI (Tl) crystal and the CsI (Na) crystal have the same diameter and are 140-220 mm. The diameter of the NaI (Tl) crystal and the diameter of the CsI (Na) crystal are the same (or the diameter of the CsI (Na) crystal is slightly larger than that of the NaI (Tl) crystal but has extremely fine difference), the diameter of the NaI (Tl) crystal and the diameter of the CsI (Na) crystal are more than 5 inches, the diameter of quartz glass used as a light guide is generally fixed at 5 inches (127 mm), and the diameter of the quartz glass corresponds to the PMT with the maximum diameter of 5 inches, and the NaI (Tl)/CsI (Na) composite crystal formed by the coating method is collectively called large-area crystal. In the field of high-energy X/gamma ray detection, the application range of the large-area composite crystal is generally not more than 220mm, and the NaI (Tl) crystal and the CsI (Na) crystal have the same diameter and are both in the range of 140 mm-220 mm, so that the coating method of the composite crystal provided by the application is more suitable for being used.
For example, the NaI (Tl) crystal has a size of phi 190 × 3.5mm, the CsI (Na) crystal has a size of phi 190 × 40mm, the quartz glass 3 has a size of phi 127 × 10mm, a 25mm wide annular region of the edge of the top surface of the NaI (Tl) crystal is polished to form an annular diffuse reflection region, and the total amount of fluorescence output in the central region is properly reduced to be consistent with that in the edge region, so that the consistency of all regions of the NaI (Tl) crystal is realized. Since the Teflon reflective film is not in contact with the liquid colloid and becomes transparent upon contact, all the operations related to the Teflon reflective film are required to be left behind and the operations related to the gluing are performed in advance to avoid the contact with the Teflon reflective film in the implementation process. In order to avoid the Teflon reflective film from adhesive failure, 1 layer of ESR reflective film is firstly adhered to the side surface of the CsI (Na) crystal and the light emergent end surface close to one side of the quartz glass through the organic silicon gel, and the thickness of the organic silicon gel is not more than 0.1 mm; then, ESR reflective films and 0.3mm thick Teflon reflective films were sequentially placed on the top surface of the NaI (Tl) crystal from the inside to the outside, and the Teflon reflective films were bent to the side surface through the top surface edge of the NaI (Tl) crystal and covered with the ESR reflective films on the side surfaces of the CsI (Na) crystal.
According to the coating method for the NaI (Tl)/CsI (Na) composite crystal, provided by the invention, the fluorescence light path generated in the central area of the crystal is adjusted by changing the surface state of the NaI (Tl) crystal, so that the high-efficiency collection of fluorescence in the crystal can be realized, and the good consistency of the response of each area of the crystal to incident photons can be ensured; in addition, the coating method does not need chamfering mechanical processing on the cylindrical crystal, and has no potential crystal cracking risk; moreover, the method can carry out gluing treatment on the side surface and the light-emitting end surface of the CsI (Na) crystal, so that the high anti-seismic performance of the crystal is ensured.
As shown in fig. 2, fig. 3 and fig. 4, the nai (tl)/csi (na) composite crystal prepared by the coating method of the composite crystal includes a nai (tl) crystal 1, a csi (na) crystal 2 and a quartz glass 3 stacked in sequence from top to bottom, wherein the nai (tl) crystal 1, the csi (na) crystal 2 and the quartz glass 3 are all cylindrical structures, the nai (tl) crystal 1, the csi (na) crystal 2 and the quartz glass 3 are aligned and bonded by a transparent silicone gel, and an annular diffuse reflection area 7 is provided at the edge of the top surface of the nai (tl) crystal 1; first reflective film 4 is provided on the side and bottom surfaces of CsI (Na) crystal 2, and first reflective film 4 covers the side and bottom surfaces of CsI (Na) crystal 2 and exposes only the side and bottom surfaces of silica glass 3; the top surface of the NaI (Tl) crystal 1 is covered with a second reflection film 5, the surface of the second reflection film 5 is provided with a third reflection film 6, and the third reflection film 6 is bent from the top surface edge of the NaI (Tl) crystal 1 to coat the side surface of the NaI (Tl) crystal 1.
Further, the first reflection film 4 is adhered to the side and bottom surfaces of the csi (na) crystal 2 by a transparent silicone gel;
the third reflective film 6 is attached to the surface of the second reflective film 5, the second reflective film 5 is pressed on the top surface of the nai (tl) crystal 1, and the edge of the third reflective film 6 is attached to the outer side of the first reflective film 4 on the side surface of the csi (na) crystal 2.
Wherein, the first reflecting film 4 is adhered on the bottom surface (the part for adhering the quartz glass 3) of the CsI (Na) crystal 2 and the side surface of the CsI (Na) crystal 2; in order to ensure the diffuse reflection characteristic of the annular diffuse reflection area 7 at the edge of the top surface of the NaI (Tl) crystal 1, the second reflection film 5 is directly attached to the top surface of the NaI (TI) crystal 1 without glue connection; and in order to stabilize the connection between the second reflection film and the nai (ti) crystal, a third reflection film capable of being adsorbed and connected is arranged on the surface of the second reflection film, the area of the third reflection film 6 is larger than that of the second reflection film 5, the third reflection film 6 covers the surface of the second reflection film 5, the third reflection film 6 is bent to the side surface of the nai (ti) crystal along the top surface of the nai (ti) crystal, and the edge of the third reflection film 6 is adsorbed and connected to the outer side of the first reflection film 4 on the side surface of the csi (na) crystal 2.
Further, the first reflective film 4 and the second reflective film 5 are ESR reflective films; the third reflective film 6 is a Teflon reflective film, which utilizes the soft film property of the Teflon reflective film to press the second reflective film 5 (here, ESR reflective film) on the top surface of the nai (ti) crystal, and reflects and collects fluorescence from the Teflon reflective film on the side surface of the nai (ti) crystal.
Further, the positional alignment includes: central axes of the NaI (Tl) crystal 1, the CsI (Na) crystal 2 and the quartz glass 3 are superposed to ensure that the fluorescence output from the composite crystal is collected with high efficiency and high reliability.
Further, in the direction of the central axis of the composite crystal, the top surface of the NaI (Tl) crystal comprises a first part facing the quartz glass and a second part outside the first part, and the width of the annular diffuse reflection area does not exceed the width of the second part, so that the fluorescent light can be efficiently collected.
Further, the NaI (Tl) crystal and the CsI (Na) crystal have the same diameter and are 140-220 mm. Therefore, the annular diffuse reflection area on the surface of the NaI (Tl) crystal is adjusted according to the crystal size, if the crystal size is small, the annular diffuse reflection area is reduced, otherwise, the annular diffuse reflection area is increased, for example, the diameter of the NaI (Tl) crystal and the CsI (Na) crystal is 190mm, and the width of the annular diffuse reflection area is 23.5 mm-26 mm, and is generally 25 mm. The design not only ensures the efficiency of fluorescence output, but also avoids chamfering the output end face and avoids the possibility of crystal breakage.
For example, the size of the nai (tl) crystal is Φ 190 × 3.5mm, the size of the csi (na) crystal is Φ 190 × 40mm, the size of the silica glass is Φ 127 × 10mm, the diameter of the silica glass is consistent with the end-window type PMT R877 of the current maximum plane size (5 inches), and the silica glass is used as a fluorescent light guide; 1 layer of ESR reflecting film is adhered to the CsI (Na) crystal side face and the light emergent end face close to the quartz glass side face through transparent organic silicon gel, and the thickness of the organic silicon gel is not more than 0.1 mm; the method comprises the steps of manufacturing an annular area, close to a side face, of a NaI (Tl) crystal top face, wherein the width of the edge of the NaI (Tl) crystal top face is 25mm, into a rough face (namely an annular diffuse reflection area 7), and the rest faces are smooth faces (namely mirror reflection areas), sequentially placing an ESR reflection film and a Teflon reflection film with the thickness of 0.3mm on the NaI (Tl) crystal top face from inside to outside, and bending the Teflon reflection film to the side face through the edge of the NaI (Tl) crystal top face and covering the ESR reflection film on the CsI (Na) crystal side face.
As shown in fig. 4 and 5, the area inside the annular diffuse reflection area 7 on the top surface of the nai (tl) crystal 1 is defined as a central area, the nai (tl) crystal and the csi (na) crystal are bonded by the transparent silicone gel, and due to the difference of the refractive indexes of the nai (tl) crystal and the silicone gel (the former is 1.85, and the latter is about 1.42), about 64% of the fluorescence generated in the central area is transmitted to the annular diffuse reflection area 7 with the width of 25mm at the edge along the radial direction of the nai (tl) crystal 1 in a total reflection manner, and then is output according to the fluorescence generated at the edge of the crystal; the remaining 36% of the fluorescence is directly output from the front. Almost all the fluorescence generated by the annular diffuse reflection area 7 rapidly enters the CsI (Na) crystal 2 through diffuse reflection, but because the fluorescence generating points are close to the edge of the NaI (Tl) crystal 1, the fluorescence generating points are easy to generate total reflection on the lower bottom surface of the CsI (Na) crystal 2 and the positions far away from the fluorescence points to return to the CsI (Na) crystal 2, and the fluorescence is output after multiple reflections, so that the total amount of the output fluorescence is reduced due to the absorption of the crystal and a reflecting film. The central region of the nai (tl) crystal 1 produces 36% of fluorescence with almost lossless output, while the remaining 64% of fluorescence is additionally attenuated by absorption of the crystal and the reflective film as it travels from the central region to the annular diffuse reflection region 7, but generally substantially matches the fluorescence output produced at the edge region of the nai (tl) crystal 1.
In the NaI (Tl)/CsI (Na) composite crystal prepared by the coating method of the composite crystal, ESR reflecting films are adhered to the side faces and the light-emitting end faces of the CsI (Na) crystal and used for reflecting and collecting fluorescence; the edge of the top surface of the NaI (Tl) crystal is an annular diffuse reflection area, an ESR reflection film is arranged on the top surface of the NaI (Tl) crystal, a Teflon reflection film is arranged on the ESR surface, the ESR reflection film on the top surface of the NaI (Tl) crystal and the Teflon reflection film are adsorbed on the crystal, and the ESR reflection film is pressed on the top surface of the NaI (Tl) crystal through the Teflon reflection film for reflecting and collecting fluorescence.
As shown in fig. 6, the present invention further provides a composite crystal detector, which includes a nai (tl)/csi (na) composite crystal prepared by the coating method of the composite crystal, wherein the quartz glass 3 of the nai (tl)/csi (na) composite crystal is coupled with the photomultiplier 8 by a light coupling agent.
Furthermore, the composite crystal detector also comprises a first shell 9 connected with the side surface of the quartz glass 3, the lower surface of the first shell is flush with the lower surface of the quartz glass, the first shell 9 and the quartz glass 3 form a closed cavity, and the NaI (Tl) crystal 1 and the CsI (Na) crystal 2 are positioned in the cavity; the first case 9 includes a Be window (not shown in the drawing) facing the nai (tl) crystal 1, and an aluminum case connecting the bottom surface of the quartz glass 3 and the Be window. The Be window is an X/gamma ray incidence window, and the composite crystal detector is an X/gamma ray detector; the sealed cavity body is composed of a Be window, an aluminum shell and quartz glass 3, the composite crystal and the cladding materials (the first reflecting film, the second reflecting film and the third reflecting film) are all placed in the sealed cavity body, dry air is stored in the sealed cavity body, and the design can prevent the crystal from deliquescing. Epoxy resin is coated on the outer side of the ESR reflecting film on the side face of the quartz glass, namely the epoxy resin is arranged between the side face of the quartz glass and the aluminum shell and below the CsI (Na) bottom face, so that the load bearing of the quartz glass is reduced, the potential danger of crystal breakage is avoided, and the anti-seismic performance of the whole composite crystal is improved.
Further, a shock absorption sleeve (not shown in the figure) is arranged on the periphery of the photomultiplier, a magnetic shielding cover (not shown in the figure) is arranged on the periphery of the shock absorption sleeve, a second aluminum shell 14 is arranged on the periphery of the magnetic shielding cover, and the second aluminum shell 14 is connected with the first aluminum shell 9. The shock absorption sleeve and the magnetic shield cover respectively play roles in shock absorption and shielding of a geomagnetic field.
In order to better understand the performance of the NaI (Tl)/CsI (Na) crystal provided by the invention, the following describes the test method and results of the performance of the composite crystal.
Since the nai (tl) crystal is the dominant crystal, the nai (tl) crystal bulk energy response characterizes the composite crystal bulk performance, for which a test system as shown in fig. 7 was designed, including the composite crystal, PMT R877, PMT readout electronics 10, multichannel analyzer MCA8000D 11, and PC 12.
The NaI (Tl)/CsI (Na) composite crystal is prepared by adopting the coating method introduced by the patent, the NaI (Tl)/CsI (Na) composite crystal is integrally placed in a closed dry cavity body formed by a Be window (X/gamma ray incidence window) and an aluminum shell, and the aluminum shell is connected with the Be window and the bottom surface edge of the quartz glass of the NaI (Tl)/CsI (Na) composite crystal to prevent the crystal from deliquescing.
The outside of the PMT R877 is provided with a silicon rubber damping sleeve and magnetic shields E989-26 which respectively play a role in damping and shielding the geomagnetic field; the PMT partial pressure relation adopts a manual to recommend the ratio, and the voltage (HV) input range is-1000V to-900V; the PMT readout electronics performs shaping (feature time 494ns), filtering (feature time 231ns), and amplification processing on the pulse signal output by the PMT R877; the MCA8000D is responsible for extracting pulse amplitude information and counting to form an energy spectrum; and the PC machine is used for displaying and analyzing the energy spectrum in real time to obtain the overall and local performance parameters of the NaI (Tl) crystal.
The present application uses a small collimation type Am-241 radioactive source 13 (about 0.5 μ Ci) to uniformly sample the surface of a composite crystal to test the local and overall performance of the crystal. The distribution of the sampled areas for the NaI (Tl) crystal surface is shown in FIG. 8, with small circle radii R of 13mm, and the circle centers are uniformly distributed on circular lines at 15.8mm (R1), 47.5mm (R2) and 79.2mm (R3) from the NaI (Tl) crystal center.
FIG. 9 provides an Am-241 spectrum of the local position output of NaI (Tl) crystal 1, and FIG. 9 shows the Am-241 spectrum of the position output of NaI (Tl) crystal 1, 4, 13 in FIG. 8, and it can be seen from FIG. 9 that the peak of the 59.5keV gamma ray spectrum is shifted to the left in order, but the difference is not large. Fig. 10 and 11 were obtained by gaussian fitting the energy spectra of the 27 positions in fig. 8; from FIG. 10, it can be seen that the amplitude of the central region of the crystal is slightly larger than that of the edge region, and the amplitude non-uniformity is only 3.0%; as shown in FIG. 11, each region has good energy resolution, preferably reaching 13.3% @59.5keV, and worst only 14.4% @59.5keV, with a non-uniformity of only 4.0%, indicating that each region of the NaI (Tl) crystal has good uniformity of photon response. The energy spectrums output by the 27 sampling areas are subjected to equal weight superposition to obtain a total energy spectrum shown in figure 12, and single Gaussian fitting shows that the integral energy resolution of the NaI (Tl) crystal can reach 14.4% @59.5 keV.
According to the coating method provided by the patent, the overall energy resolution of NaI (Tl) crystals (phi 190 multiplied by 3.5mm) in the composite crystals can reach 14.4% @59.5keV, which is very close to the limit energy resolution of a small-size NaI (Tl) crystal detector 11%, and also exceeds the design indexes of 15% @59.5keV of a PDS detector (NaI (Tl) diameter 160mm) on a BepposAx satellite and a hard X-ray detector (NaI (Tl) diameter 183mm) on a HEXTE satellite. The composite crystal provided by the invention has good resolution and good performance.
The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by a person skilled in the art that the scope of the invention as referred to in the present application is not limited to the embodiments with a specific combination of the above-mentioned features, but also covers other embodiments with any combination of the above-mentioned features or their equivalents without departing from the inventive concept. For example, the above features may be replaced with (but not limited to) features having similar functions disclosed in the present application.
Claims (9)
1. A method for coating a composite crystal, comprising the steps of:
s101: grinding and polishing the surfaces of NaI (Tl) crystals and CsI (Na) crystals to ensure that the NaI (Tl) crystals and the CsI (Na) crystals are clean and bright;
s102: aligning the NaI (Tl) crystal, the CsI (Na) crystal and quartz glass from top to bottom, sequentially stacking the NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass, and bonding the NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass into a whole through transparent organic silicon gel;
s103: after the glue is cured, adhering a first reflecting film on the side and bottom surfaces of the CsI (Na) crystal through a transparent organic silicon gel;
s104: polishing the edge of the top surface of the NaI (Tl) crystal to form an annular diffuse reflection area;
s105: covering a second reflecting film on the top surface of the NaI (Tl) crystal, covering a third reflecting film on the surface of the second reflecting film, bending the third reflecting film to the side surface of the NaI (Tl) crystal along the edge of the top surface of the NaI (Tl) crystal and covering the first reflecting film connected with the side surface of the CsI (Na) crystal;
the third reflecting film is attached to the surface of the second reflecting film and covers the second reflecting film on the top surface of the NaI (Tl) crystal in a pressing mode;
the first and second reflective films are ESR reflective films; the third reflecting film is a Teflon reflecting film;
the NaI (Tl) crystal and the CsI (Na) crystal have the same diameter and are 140-220 mm.
2. The method of cladding a composite crystal according to claim 1, wherein the positional alignment comprises: the central axes of the NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass are coincident.
3. The method according to claim 2, wherein the top surface of the nai (tl) crystal includes a first portion facing the silica glass and a second portion outside the first portion in the direction of the central axis of the composite crystal, and the annular diffuse reflection area has a width not exceeding the width of the second portion.
4. A composite crystal detector comprising a composite crystal produced by the coating method according to any one of claims 1 to 3, the composite crystal comprising a nai (tl) crystal, a csi (na) crystal, and silica glass, which are stacked in this order from top to bottom, the silica glass of the nai (tl)/csi (na) composite crystal being coupled with a photomultiplier tube by a photo-coupling agent; wherein
The NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass are all cylindrical structures, the NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass are aligned in position and are connected through transparent organic silicon gel in an adhesive mode, and an annular diffuse reflection area is arranged at the edge of the top face of the NaI (Tl) crystal; first reflecting films are arranged on the side surfaces and the bottom surface of the CsI (Na) crystal, and the first reflecting films cover the side surfaces and the bottom surface of the CsI (Na) crystal and only expose the side surfaces and the bottom surface of the quartz glass; the top surface of the NaI (Tl) crystal is covered with a second reflection film, the surface of the second reflection film is provided with a third reflection film, and the third reflection film is bent from the top surface edge of the NaI (Tl) crystal to wrap the side surface of the NaI (Tl) crystal;
the first reflective film is adhered to the sides and bottom of the CsI (Na) crystal by a transparent silicone gel;
the third reflecting film is attached to the surface of the second reflecting film and covers the second reflecting film on the top surface of the NaI (Tl) crystal in a pressing way, and the edge of the third reflecting film is attached to the outer side of the first reflecting film on the side surface of the CsI (Na) crystal;
the first reflective film and the second reflective film are ESR reflective films, and the third reflective film is a Teflon reflective film.
5. The composite crystal detector of claim 4, wherein the positional alignment comprises: the central axes of the NaI (Tl) crystal, the CsI (Na) crystal and the quartz glass are coincident.
6. The composite crystal detector of claim 5, wherein the top surface of the NaI (Tl) crystal includes a first portion facing the quartz glass and a second portion outside the first portion in a direction of the central axis of the composite crystal, the annular diffuse reflection area having a width not exceeding a width of the second portion.
7. The composite crystal detector of claim 4, wherein the NaI (Tl) crystal and the CsI (Na) crystal have the same diameter and are 140-220 mm.
8. The composite crystal detector of claim 4, further comprising a first shell attached to the side of the quartz glass, the first shell lower surface being flush with the lower surface of the quartz glass, the first shell and the quartz glass forming a closed cavity, the NaI (Tl) crystal and the CsI (Na) crystal being located within the cavity;
the first enclosure includes a Be window facing the nai (tl) crystal, and a first aluminum shell connecting the side of the quartz glass and the Be window.
9. The composite crystal detector of claim 8, wherein a shock absorbing sleeve is disposed around the photomultiplier tube, a magnetic shielding cover is disposed around the shock absorbing sleeve, and a second aluminum shell is disposed around the magnetic shielding cover and connected to the first aluminum shell.
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