Investigation Of Field Emission Based Carbon Nanotube Microfocus X-ray Technology

With the wide applications of X-ray technology in medical,industrial and analytical fields,there are increasing demands on improvements of the resolution,stability,lifetime properties.Tungsten filaments are adopted as hot cathodes in traditional X-ray tubes.Some disadvantages are related to hot electron emission,including large volume,slow start,and low efficiency.Meanwhile,it is difficult to make the hot filament down to micron scale due to material and manufacturing limitations,resulting low spatial resolution,thus,it is hard to meet the requirement of high resolution imaging.The carbon nanotube(CNT)field emission cathode,which has advantages of low thermal consumption,fast response,high resolution,and capability of multiple beam integration,is one of the important R&D fields of the X-ray tube.In this thesis,CNT field emission based micro focus X-ray technology is investigated.The CNT field emitters are grown on the metal substrates directly by thermal chemical vapor deposition,combining with surface anodizing process.Comparing with the traditional catalyst film based CNT emitters,the direct grown CNT emitters have advantages of strong adhesion,long lifetime,and excellent emission stability.The emission current density of such cathodes can reach 400 mA/cm~2,with the turn-on electric field of 1.44 V/?m.In this work,we designed and optimized the structure and potential setups of the cold cathode X-ray tube with the aid of computer simulation,by calculating the electron trajectories and investigating the effects of electrostatic parameters on electron beam focusing.We built the dynamic X-ray imaging system.Under the anode voltage of 19 kV,the anode current of 35?A,and the exposure time of 6 s,clear images are reached for biological samples(i.e.,hippocampus)and electronic devices.According to the X-ray machine image resolution test card,the X-ray image of the resolution phantom can reach 2.5 lp/mm(lp denotes line pair),where the flat-panel detector resolution reaches 200?m.