Researches On Key Technologies Of Miniature X-ray Source

Portable X-ray fluorescence analysis instruments,which is based on elementscharacteristic X-ray physical properties,has been widely used in many areas and fieldsat home and abroad.Miniature x-ray source is one of the key components of theportable X-ray fluorescence analysis instrument. Commercial portable fluorescenceanalyzer, basically using the the foreign ceramic craft package x-ray source, theinternal structure and fabrication process are confidential. Domestically producedx-ray source oriented to the field of non-destructive testing, medical imagingapplications. The portable fluorescence analysis applications,have raised higherrequirements for the X-ray source stability, size, power consumption, efficiency andspeed of responseThis paper studies comes from a863plan resources in the field of environmentaltechnology topics “high-precision ray detection equipment R&D "（Project No.:2012AA061803）. Physical design and experimental studies are carried out on thebasis of Theoretical analysis and simulation of the internal structure for the directthermal ceramic package end window anode structure of miniature X-ray source. Thework and achievements of the papers are as follows:1. Designed and developed a new metal ceramic package miniature X-raysource,which has broke the blockade of foreign technology, provides a new type ofX-ray excitation source of portable X-ray fluorescence analysis.2. Established the structure and designing technological process of the miniatureX-ray source by domestic and international research and parsing similar products. Forthe miniature X-ray source,the electron emission system is thermal emission,theelectron beam focusing is electrostatic focusing,the anode is end windows transmissionstructure, and the package is ceramic structure.3. Fundamental research to provide a theoretical basis for the physical design hascarried out for the components of the micro X-ray source. （1） The emission current relative deviation as an index to evaluate the uniformityof emission current of the cathode emitter, and obtain the cathode filament temperaturedistribution rule. This provides a theoretical reference for the filament structural design.（2） The ideas proposed using Eddington formula to calculate the averagethickness of the miniature X-ray source target,and obtain the different material target’saverage thickness value bombarded by different energy electron beam. Theoreticallyproved that the miniature X-ray source target average thickness of1-5μm.（3） Theoretical analysis and Monte Carlo simulations verify that the maximumintensity of the emission characteristic X-ray in the direction of the angle between thesurface of the anode into1⁴o. This has certain theoretical significance for thestructural design of the X-ray source and the monochromatic X-ray applications.4. EDA technology introduced into the structural design of miniature X-raysource, to carry out the the tube electronics kinematics simulation design. Using CSTParticle Studio software to build a micro-simulation model of the X-ray source,analysis the internal electric field of the X-ray source, the electric potentialdistribution, electron trajectory and the emission current, obtain the electron beamfocal spot shape, anode charge density distribution,electron energy, electron velocityvariation and emission current value, scan and optimize of the structural parameters ofthe various components. The results show that: the electrostatic focusing electronbeam trajectory control is feasible, the largest electronic movement speeds of up to1.2×10⁸m/s, electron acceleration in a very short space between the shield and theanode cap, the the center maximum charge densityup to the3×10^-8C/m³filamentemission current up to50μA.5. Researching the steady-state temperature rise of the cathode, anode and shellsurface by the Use of co-simulation technology with CST multi-physics studio andparticles studio software. The results show that: the main heat source of the miniatureX-ray source concentrated in the vicinity of the cathode filament center, the shellmaximum temperature of59°C, the maximum thermal power loss on the anode targetcenter density of2.9×10⁸W/m³, and the maximum temperature is about44℃.6. Designed and produced miniature X-ray tube, and performance testing. Theexperiments show that: for the trial produced miniature X-ray source, maximumemission current of80μA or more,emitted X-ray spectral distribution is basically thesame with the foreign products. So directly heated cathode structure is able to meet theapplication requirements of the miniature X-ray source.