| Since the discovery of X-ray for a century,thermal electronic source has been widely used in various X-ray applications because of its advantages of easy manufacture and standardization.It was at the core of X-ray application technology.However,with the development of computer tomography,Airport security,medical radiotherapy and other medical&scientific fields,the traditional thermal electronic source X-ray tube has been limited in many applications for its slow time response and large physical size.People are interested in achieving fast electron beam pulse,reducing X-ray dose,improving image contrast,enhancing spatial resolution and time division.The fabrication technology of new X-ray source with high resolution has aroused great interest.The need of application drove the development of technology.Field emission electron source can provide electron beam with highly controllable,high quality and high quality energy distribution,which is considered as a promising alternative to thermal electronic source.When combined with the emerging field of nanomaterials,especially carbon nanotubes,field emission electronic sources present unique technological advantages and opportunities.Compared with thermoelectric X-ray tube,carbon nanotubes X-ray tube(CNTs X-ray tube)has an unignorable advantage of performance and technologyThe common carbon nanotubes X-ray tubes mostly adopted grid-controlled triode structure.The grid structure and cathode are aligned.When the grid was applied hogh positive voltage,the cathode electrons emitted.This structure had the advantages of pulse emission and fast response,but there was a certain amount of interception of electrons in the grid,which wasted the effective current and caused power loss.Electron impact transferred energy to the grid.With the accumulation of working time,the temperature of the grid rose.Metal deformation affected the stability of current emission and made the imaging effect worse.In extreme cases,high temperatures could burn cathodes and damage devices.The interception of electrons by grids limited the high current application of carbon nanotubes X-ray tubes.The development of low interception carbon nanotubes X-ray tube had its technical necessity and practical application needsThis paper focused on the preparation of electron guns with low gate interception ratio using carbon nanotubes as cathode emission emitter.Carbon nanotubes(CNTs)have very high aspect ratio and excellent conductivity.When they are in good electrical contact with the substrate,they can produce excellent electronic emission properties under an external electric field.The preparation methods of carbon nanotube cathode in this paper was screen printing.It printed batch carbon nanotubes on metal substrates by wet chemical method.The main research results are as following:1.CNTs field emission emitter were prepared by screen printing respectively.Ethyl cellulose was added to the printing paste to increase the paste consistency,reduce the spread of the paste after printing,and improve the precision of the printing line.At least,0.2 mm wide lines could be printed.Micron-sized metal particles were added to the paste,and alloy structure was formed on the base surface after vacuum heat treatment,forming a stable adherence and low contact resistance.In the diode test,the emission current of the strip emitter of 4mm×0.3mm is 38m A,and the emission current density is 3.16A/cm~2.2.Designed and optimized the structure of the electron gun using the electron beam simulation software.In the simulation,we adjusted the relative relationship between the CNTs emitter unit and the mesh size to find the smallest interception of electrons by the grid.When the cathode emission unit was 190?m square and the mesh size was 200?m square,the electron passed the gate without interception.In the simulation,the focal spot size of 2mm×0.4mm strip emitter on the anode target was 0.2mm×0.1mm.The electron gun scheme had excellent focusing performance.3.Developed the triode electron gun according to the design parameters.In the I-V test of triode,the interception rate of cathode grid electrons by screen printing was about 15%.The low intercept cathode was assembled into an electron gun,which was packaged into an X-ray tube after exhaust and sealing.The anode of the X-ray tube had an anode target angle of 20 degrees.The emission current and imaging performance of the packaged X-ray tube were tested.The I-V characteristic of X-ray tube was consistent with that of electron gun.In the X-ray DR imaging test,the inner line of PCB plate was clearly visible,and the image of human hand was clear without ghosting.It could adjust the anode voltage to image the metal structure with different penetration. |
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