CN1014478B - X-ray photocathode, image enhancer and imaging instrument - Google Patents
X-ray photocathode, image enhancer and imaging instrumentInfo
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- CN1014478B CN1014478B CN 88102912 CN88102912A CN1014478B CN 1014478 B CN1014478 B CN 1014478B CN 88102912 CN88102912 CN 88102912 CN 88102912 A CN88102912 A CN 88102912A CN 1014478 B CN1014478 B CN 1014478B
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Abstract
The present invention discloses an X-ray photocathode, an image enhancer and an imaging instrument thereof, and relates to a vacuum photoelectric imaging device and an X-ray imaging detector. The present invention provides the X-ray photocathode sensitive to a medical X-ray wave band, and correspondingly realizes an X-ray image enhancer working in a direct conversion mode and a miniature portable lower intensity X-ray imaging instrument made of the device. The device comprises the photocathode, a microchannel plate and an output fluorescent screen, and adopts a proximity focusing structure. The imaging instrument comprises the enhancer, a miniature X light source and a miniature high voltage device. The present invention is widely suitable for medical perspective diagnosis, industrial nondestructive inspection, structural perspective, security perspective examination, etc.
Description
The present invention relates to a kind of vacuum photoelectric imaging device.
General X ray casting image intensifier all is to adopt the indirect conversion working method at present, X-ray that sees through measured object that is the X source radiation at first is input phosphor screen or scintillation crystal absorption, convert optical photon output to, this faint optical photon stream converts photoelectron to through the visible light photocathode again and is accelerated or doubles, bombardment output phosphor screen has strengthened about 5000～10000 times visible fluorescence and has resembled output thereby obtain to resemble corresponding brightness with the transmission of measured object X ray.The luminance gain part is accelerated from photoelectron, part dwindling from image area.Adopt the electrostatic focusing mode that photoelectron is resembled inverted image and transfer to the output phosphor screen, graphics area generally dwindles 100 times.This X ray casting image intensifier input typically has a diameter from 6 inch to 9 inch, and it is bulky, can only be fixed on the laboratory and use.In addition, input phosphor screen or scintillation crystal and visible light photocathode are prepared in the two ends of transparent carrier respectively, thus phenomenon such as regular meeting's generation phosphor screen or contaminated its luminous efficiency that makes of scintillator descend greatly on technology, and luminosity is inhomogeneous.Secondly, carrier must have very high transparency to visible light, and thickness must be reduced to below the 50 μ m, otherwise will influence the resolution of device.Thereby preparing the big extremely thin again transparent body of this area, difficulty is very big on technology.Add that visible light photocathode preparation technology is complicated, thereby the device yields is low.The cost height costs an arm and a leg.
The patent that the U.S. once proposed a kind of flat single-stage proximity focusing X ray casting image intensifier and proposed the plural serial stage structure subsequently.Though device volume has dwindled, the shortcoming that conversion efficiency is low also must be improved, and technologic complexity and difficulty are more outstanding.
United States Patent (USP) 4142101 has been described the image device of a kind of low-intensity X ray and r ray, and it remains the X ray casting image intensifier of the indirect conversion mode work of adopting scintillation crystal.But it adopts and the microchannel plate of visible light photocathode proximity focusing strengthens photoelectron stream, and multiplication constant can reach 10
3～10
4This device volume is little, can obtain higher conversion efficiency, but incident X-rays converts the end that the scintillator layers of visible light need be prepared in the input optical fibre panel window contact atmosphere of visible light casting image intensifier to.What constitute scintillator is as CsI(Na), CsI(TI) a class alkali halide, very easily the moisture absorption is rotten in air for they, must sealed damp-proof.Can decay the inevitably X ray intensity of incident of encapsulant; Though the while fibre faceplate can transmit visible light and resemble quite perfectly, optical loss is at least more than 30%; Moreover, needing to adopt the visual fibre faceplate that dwindles for enlarging the visual field, this expensive special optical fiber panel has not only increased optical loss, and has reduced resolution.In this device, there is insurmountable contradiction between sensitivity and the resolution:, must thicken scintillator layers for improving absorption to incident X-rays; And scintillator layers thickness increases, and then the visible light that produces therein will be scattered when passing scintillator layers, thereby resolution is descended.Therefore, still there are all shortcomings of X ray casting image intensifier of indirect conversion mode work in this device.
Realize the X ray casting image intensifier of direct conversion regime work, key is the efficient photocathode of seeking the X ray sensitivity, J.E.Bateman is once at Advances in Electronics and Electron Physics 52189(1979) in reported a kind of photocathode to the X ray sensitivity, it is made up of cathode substrate and cathode emitter layer, cathode substrate adopts aluminium foil, and thickness is 5 μ m.Emitter layer adopts cesium iodide, and thickness is 200～500 μ m, is loose uniform density structure.Its relative density is 5%, i.e. 0.18g/cm
3Its shortcoming is that it only has bigger response to energy less than the photon of 10Kev, improves as energy, and then the quantum efficiency variation is not suitable for the medical X-ray wave band of energy at 20～50Kev.
One of purpose of the present invention provides a kind of X ray casting image intensifier that adopts the proximity focusing conversion image of direct conversion regime work.Guaranteeing have on the basis of suitable conversion efficiency, it has the resolution height, volume is little, technology is simple, yields is high, low cost and other advantages, thereby has cancelled expensive fibre faceplate and eliminated a series of shortcomings of bringing owing to the employing scintillation crystal.
Two of purpose of the present invention provides a kind of portable small-sized low-intensity X ray imaging instrument that adopts above-mentioned X ray casting image intensifier, have volume little, in light weight, be easy to carry, need not special protection and characteristics such as can in bright chamber, observe, be applicable to the fields such as perspective, diagnosis and flaw detection of X ray.
The key that realizes above-mentioned purpose is to propose a kind of X ray photocathode to required X ray wave band sensitivity, realize the directly working method of conversion, promptly convert photoelectronic indirect conversion mode again to without converting optical photon earlier to from sightless X-ray, but be directly changed into the working method of photic electronics, thereby scintillation crystal and fibre faceplate in the above-mentioned existing X ray casting image intensifier have been cancelled.
Direct conversion work mode of the present invention is made up of cathode substrate and cathode emitter layer the X ray photocathode of required X ray wave band sensitivity, and cathode substrate adopts light metal paper tinsel, for example aluminium foil.Emitter layer adopts alkali halide, the higher cesium bromide of cesium iodide or sensitivity for example, and adopt dense layer to add the variable density structure of weaker zone, promptly there is a dense layer on the cathode substrate surface as substrate layer, is that density is the weaker zone that reduces to change from the dense layer surface to emitting surface.The thickness of dense layer is 1～2 μ m, and density is 50～100%, i.e. 2～4g/cm
3, be preferably 70%, about 3g/cm
3The thickness of weaker zone is 100～300 μ m, is preferably about 250 μ m, with weaker zone and the dense layer junction section start as weaker zone, the density of section start is 30～50%, is preferably 50%, and the density of emitting surface is 2～5%, be preferably 2%, averag density is 10%, i.e. 0.4g/cm
3, the variable density in the middle of it can be to reduce continuously, also can be discontinuous reducing.
The thickness of aluminium foil selects to consider the attraction of electrostatic field when it both can bear proximity focusing, again the photon energy of the X ray wave band that passed through is not had obvious decay.
The material of emitter layer is selected to consider that high secondary electron yield is arranged.In order to improve secondary efficient, emitter layer can be made the loose shape structure more much lower than normal density, because open structure has the average escaped depth of the secondary electron more much bigger than compact structure, it mainly plays emission secondary electron layer, and dense layer mainly plays the incident X-rays absorbed layer, excites a photoelectron of generation to be transported to weaker zone at this layer and excites the secondary electron that produces low energy again.In a word, the photocathode of this variable density structure had both guaranteed that X ray was had higher absorption efficiency, had higher secondary electron escape probability again.
Existing vacuum type X ray casting image intensifier is owing to adopt the indirect conversion working method, so it is by moisture seal device, X ray scintillation crystal, optical fibre face plate, visible light photocathode, and compositions such as microchannel plate, output phosphor screen and magnifying glass.The vacuum type X ray casting image intensifier of the proximity focusing of the direct conversion regime work of employing provided by the present invention conversion image by input window, adopt dense layer add weaker zone variable density structure the X ray photocathode, form with the microchannel plate of photocathode proximity focusing with the output phosphor screen of microchannel plate proximity focusing etc.The cathode emitter layer also can directly prepare on the input face of microchannel plate, saves the cathode substrate that the light metal paper tinsel is done.
Portable low-intensity X ray imaging instrument X source of the present invention, adopt mini X-ray pipe or radioactive isotope power supply, the X ray casting image intensifier adopts the vacuum type X ray casting image intensifier of the proximity focusing conversion image of above-mentioned direct conversion regime work, be that the photocathode of X ray casting image intensifier adopts dense layer to add the emitter layer of weaker zone variable density structure, photocathode and microchannel plate proximity focusing; Also has high pressure generator, so that X-ray pipe high pressure and each voltage of X ray casting image intensifier are provided.Install light shield additional at output phosphor screen end, except that the ray perforation hole, install lead rubber additional at the remainder of mini X-ray pipe and shield.The emitter layer that also can adopt dense layer to add weaker zone variable density structure directly prepares the vacuum type X ray casting image intensifier of the direct conversion regime work on the microchannel plate input face, promptly with the cathode substrate of microchannel plate input face as photocathode.When adopting radioactive isotope power supply, need not power supply, more meet the miniaturization requirement, cost an arm and a leg but prepare heavy dose of radioactive source as X source, and because radioactive source
125The half-life of I, have only half a year useful life, be good so use the mini X-ray pipe at present as X source.The high pressure generator of conventional X ray imaging instrument adopts electric main to constitute through transformation, multiplication of voltage.The Industrial Frequency Transformer volume of this 50HZ is big and heavy, and filtering need be with the high voltage bearing capacitor of big capacity, and voltage regulation performance is poor.Small-sized in order to realize, portable, high voltage source must be microminiaturized, adopt the high-frequency impulse oscillating voltage through boost, multiplication of voltage obtains each required high pressure.
Compare with existing X ray casting image intensifier, the present invention adopts the X ray photocathode to required X ray wave band sensitivity, realized the working method of direct conversion, promptly convert photoelectron again to without converting optical photon earlier to, but formula is put in the work that is directly changed into photic electronics from sightless X-ray.Scintillation crystal and fibre faceplate in the conventional X ray casting image intensifier have been cancelled.Thereby new device neither needs to prevent the seal protecting device of scintillator layers deliquescence, eliminated the luminous energy loss in fibre faceplate, overcome again because the thicker difficulty that causes resolution to descend of scintillator layers.Though the X ray photocathode is also thicker, photocathode is loose shape structure, and X ray scattering therein is less, thereby can not make the resolution performance depreciation.The X ray photocathode directly can also be prepared on the microchannel plate.So the resolution performance of new device can not be subjected to having a strong impact on of X ray photocathode thickness.The resolution of existing small-sized X ray casting image intensifier is 3～4lp/mm, and the resolution of new unit of the present invention may ultimately reach 20lp/mm.Image transmits by 1: 1 size.The output image size is more existing big 4 times, need not to amplify with magnifying glass again, and human eye can be directly visual.
Another advantage that adopts the X ray photocathode is that this negative electrode can prepared beforehand, transfers to dynamic checkout unit then and carry out performance test in dry air.Qualified negative electrode takes out from dynamic checkout unit, is assemblied in the shell of device under dry inert gas (as nitrogen) protection.The X ray photocathode can be selected before the device of packing in advance.After being fitted into device, performance does not have significant change, thereby has improved the yields of X ray casting image intensifier greatly, simplified technology, has avoided pollution phosphor screen that preparation visible light photocathode runs into often fully, has increased problem such as bright background.Device cost is reduced significantly.
The portable low-intensity X ray imaging instrument that the present invention proposes is in light weight, and volume is little, and cost is low, and power consumption is little.X ray intensity is low, and is safe and reliable, can be in any bright chamber or field condition use, not only can make radioscopy, and can be used for detecting the internal structure or the defective of layer material the human limb bone.
Provide embodiments of the invention below in conjunction with accompanying drawing.
Fig. 1 is the X ray photocathode structural representation that the present invention adopts.(6) are the light metal paper tinsels as aluminium foil one class among the figure, thick about 50 μ m.The attraction of electrostatic field but also the photon energy of the X ray wave band that passed through do not had obvious decay when thickness selects to make it not only can bear proximity focusing.Preparation one deck gross thickness reaches the high material (7) of secondary electron yield of 250 μ m on aluminum foil substrate, as CsI, and CsBr one class alkali halide.It is after emitter absorbs high energy X photon (4) that known X ray causes photoemission mechanism, excite a photoelectron (and high energy Auger electronics of a very little part) that produces high energy, each photoelectron excites the secondary electron that produces a plurality of low energy with emitter atomic collision in transport process, they are transported to surface effusion formation X ray and cause photoemission current (8) under electric field action.In order to improve secondary efficient, emitter layer can be prepared into the loose shape structure more much lower than normal density.The preparation method adopts slowly evaporation in inert gas.Provided density distribution schematic diagram in the emitter among Fig. 1 simultaneously.Transverse axis represent apart from substrate apart from l, the longitudinal axis is represented the density p of emitter layer.From near the substrate to emitting surface, density roughly is and descend distributes.The change of density be by when evaporation control inert gas pressure realize.As adopting argon, its pressure changes in 0.05 torr～10 torr scopes in the evaporation process.Beginning is evaporated alkali halide under high vacuum, the inert gas pressure when raising evaporation then gradually, and the result just forms the low more photocathode layer of past more superficial density.The dense layer of X ray photocathode mainly plays incident X line absorption layer.Excite a photoelectron of generation to be transported to weaker zone at this layer and excite the secondary electron that produces low energy again.Because open structure has the average escaped depth of the secondary electron more much bigger than compact structure, thereby weaker zone mainly plays emission secondary electron layer.The photocathode of this variable density structure, both having guaranteed has higher absorption efficiency to X ray, has higher secondary electron escape probability again.As another kind of mode, also cathode layer can be prepared on little logical plate input face.Need not aluminum foil substrate this moment.
With the X ray photocathode, microchannel plate, the shell that the output phosphor screen is packed into and is made of the input and output windowpane vacuumizes then, and after long-time pump-down process, envelope is (vacuum degree～8 * 10 down
-7Torr) promptly finishes.
For example the surface of emission of emitter layer is 0.4mm apart from the input face of microchannel plate, the output face of microchannel plate and the plane of incidence of thin aluminium lamination distance are 3mm, zero potential is got in the microchannel plate output face during work, the voltage of cathode substrate is-1600～-1800V, the operating voltage power-900 of microchannel plate～-1100V, the voltage of the thin aluminium lamination of output before the phosphor screen is+6～+ 7KV.If adopt negative electrode directly to be prepared on the microchannel plate input face, on the microchannel plate operating voltage get-1000～-1200V, other is constant, then cutout screen brightness can reach 20Cd/m
2
Fig. 2 is the small-sized X ray casting image intensifier structural representation that the present invention proposes.
X ray (2) irradiation of X source (1) radiation is to measured object (3).The X ray that penetrates (4) incides on the X ray photocathode (7) through the input window (5) of X ray casting image intensifier (14) and thin light metal (as aluminium) layer (6).The light metal layer is the substrate of negative electrode, is again the electrode of negative electrode.After the X ray photocathode absorbs X-ray of incident.Be directly changed into X-ray and send a telegraph son (8), under electric field action outside the effusion photocathode layer.The electron density distribution of overflowing distributes corresponding with the Transmission X photon density of the measured object of incident.They inject the input of microchannel plate (9) and in microchannel plate the multiplication after, the electron beam (10) that has doubled in its output outgoing, the electron beam that has doubled passes the output phosphor screen of thin light metal (as aluminium) layer (11) bombardment that is plated on phosphor screen (12) front and the proximity focusing of microchannel plate output under the accelerating voltage effect.So just on cutout screen, directly demonstrate the visible light that brightness corresponding to measured object radioscopy elephant strengthened and resemble, by direct visual this image of output window (13) observer.
Fig. 3 is small-sized X ray casting image intensifier and the mini X-ray pipe that adopts the present invention to propose, the structural representation of the low-intensity X ray imaging instrument that high-pressure mini power supply (15) constitutes.Owing to be in bright chamber, to use, behind X ray casting image intensifier output window, install light shield additional, light is to observing the influence of cutout screen image around avoiding.X source can adopt radioactive isotope power supply (as
125I) it need not power supply, more meets the miniaturization requirement.The present invention adopts the mini X-ray pipe to make X source.The X ray imaging is not adopted the expensive X-ray of the big price of volume to learn element and is focused on, but utilizes simple projection imaging principle.This requires radiation source to approach point-source of light.But dwindle X-ray pipe focal spot, target stream can only be limited in very little level, otherwise, can make the focus place heating fusing of X-ray pipe target material very soon.For requiring to have certain X ray intensity output, the mini X-ray lightpipe optics focus that the present invention adopts is 0.3 * 0.3mm
2Require measured object enough far away like this, just picture resolution preferably can be arranged apart from X source.And the brightness of distance cutout screen far away more is just low more.The low-intensity degree X ray imaging instrument that the present invention proposes makes X ray casting image intensifier and X-ray tube pitch from adjustable, and as an example, ultimate range can reach 25cm.Press about 40KV～50KV as medical purposes X-ray pipe target; As commercial Application, look the difference of measured object, the target pressure＞50KV of X-ray pipe.
In order to realize the high voltage source microminiaturization, the circuit block diagram that the present invention proposes high voltage source as shown in Figure 4.Adopt the high-frequency impulse oscillating voltage through the multiplication of voltage of boosting obtain required each high pressure, this has just reduced the volume and weight of transformer greatly, has reduced the requirement to filter capacitor.X-ray pipe and X ray casting image intensifier voltage all belong to adjustable, easy to use.
(25) are civil power among Fig. 4, (16) be switching power supply, (17) be low-tension transformer, (18) are rectification circuit, and (19) are voltage stabilizing circuit, (20) be oscillator, (21) be amplifying circuit, (22) are high-frequency step-up transformer, and (23) are voltage multiplie, (24) be voltage divider, (1) is the X-ray pipe.
Below provide the embodiment that weaker zone density is continually varying X ray photocathode.
In container for evaporation, fill the argon gas of 0.1 torr, the CsI(of about 150～250mg or CsBr) place in the crucible of tantalum piece composition, in 2～5 minutes, all material in the crucible is slowly evaporated, in evaporation, fill into argon gas continuously, Ar Pressure rises to 5 torrs gradually when evaporation finishes.The result can form density from substrate layer to emitting surface continually varying X ray photocathode.
Below provide another embodiment of the X ray photocathode that weaker zone density changes in gradient again.
Contain CsI(or CsBr in the tantalum piece crucible) with 150～250mg, in container, fill argon gas with 0.1 torr, in 2～5 minutes, all material in the crucible is slowly evaporated, under 0.1 torr argon gas, evaporated 15～40 seconds, and then fill into argon gas to 0.5 torr evaporation 15～40 seconds, progressively Ar Pressure is increased to 0.8 torr, 1.0 torrs, 1.2 torrs, 1.4 torrs, 1.6 torrs, 2 torrs, 3 torrs, 4 torrs, 5 torrs respectively, evaporation time is identical at every turn, up to material is all evaporated.
Claims (2)
1, a kind of vacuum type X ray casting image intensifier, be provided with photocathode, play the microchannel plate and the output phosphor screen of electronics multiplication, photocathode is made up of cathode substrate and cathode emitter layer, cathode substrate adopts light metal paper tinsel (for example aluminium foil), emitter layer adopts alkali halide, proximity focusing between microchannel plate and the output phosphor screen, the present invention is characterized in that photocathode is that emitter layer adopts dense layer to add the X ray photocathode of weaker zone variable density structure, promptly at cathode surface one thickness being arranged is 1～2 μ m, density is 50～100%, i.e. 2～4g/cm
3Dense layer as substrate layer, be that density is and reduces to change from dense layer surface to emitting surface, the thickness of weaker zone is 100～300 μ m, the density of section start is 30～50%, emitting surface density is 2～5%, photocathode and microchannel plate proximity focusing.
2, casting image intensifier as claimed in claim 1, the emitter layer that it is characterized in that said photocathode adopts cesium iodide or cesium bromide, its dense layer to weaker zone density therebetween changes or discontinuous variation by continuous, the density of dense layer is preferably 70%, the density of weaker zone section start is preferably 50%, and the density of emitting surface is preferably 2%.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 88102912 CN1014478B (en) | 1988-05-13 | 1988-05-13 | X-ray photocathode, image enhancer and imaging instrument |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 88102912 CN1014478B (en) | 1988-05-13 | 1988-05-13 | X-ray photocathode, image enhancer and imaging instrument |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1032989A CN1032989A (en) | 1989-05-17 |
| CN1014478B true CN1014478B (en) | 1991-10-23 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 88102912 Expired CN1014478B (en) | 1988-05-13 | 1988-05-13 | X-ray photocathode, image enhancer and imaging instrument |
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Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1048578C (en) * | 1994-02-08 | 2000-01-19 | 上海华科电子显象有限公司 | Plate type x-ray image enhancement device and the mfg. method |
| CN101404237B (en) * | 2008-09-01 | 2010-06-16 | 西安理工大学 | Image intensifier for improving detection performance of low-light level imaging system at normal temperature |
| CN102625555A (en) * | 2012-04-05 | 2012-08-01 | 无锡日联科技有限公司 | Physical focusing micro-focus X-ray source capable of being used on continuous working condition |
| CN103462627A (en) * | 2013-09-22 | 2013-12-25 | 江苏美伦影像系统有限公司 | High-sensitivity imaging chain system |
| CN107765287B (en) * | 2017-11-20 | 2023-11-14 | 中国工程物理研究院激光聚变研究中心 | Nuclear leakage detector and method for detecting pollution source by using same |
| CN113589637B (en) * | 2021-06-18 | 2023-12-01 | 中国工程物理研究院激光聚变研究中心 | Hard X-ray sensitive framing camera |
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1988
- 1988-05-13 CN CN 88102912 patent/CN1014478B/en not_active Expired
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| CN1032989A (en) | 1989-05-17 |
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