A carbon nanotube (CNT) emitter-based high-speed micro-computed tomography (CT) system is designed herein. CT scans result in prolonged exposure to radiation, thus, pulsed-field emission is performed to generate pulsed X-rays to reduce radiation dose. The radiation dose rates of continuous X-rays and X-rays generated by different pulses were compared. X-rays were stably generated 40 times per second through a pulsed-field emission current with MOSFET circuit. The CNT field emitter characteristic was maintained for more than 35 hours continuously, which means more than 5 million X-ray shots can be taken when sufficient current flows on pulse mode. X-ray images were also successfully acquired through such pulse driving.
KEYWORDS: Radiation effects, Beryllium, 3D modeling, Scanning electron microscopy, Radiation oncology, Radiotherapy, Particles, Metals, Medicine, Medical research
Radiation research primarily aims to improve radiation therapy and the use of radiation on soft materials. There are many reports available on the effects of high-dose radiation on cells, but the effects of low-dose radiation still require much scientific evidence. Therefore, we intend to study the effects of low-dose irradiation on cell internal structures by cold cathode field emission carbon nanotube (CNT)-based cell irradiator. Hence, we designed a CNT-based microbeam system to irradiate cells. CNT emitter was fabricated by synthesizing CNTs on point shaped substrate. The growth of CNTs was confirmed by scanning electron microscope (SEM). The aging process was carried out to improve the performance of the CNT emitter and the I-V characteristic was measured. We also conducted the simulation study in order to confirm the electric field change and the electron beam trajectory.
We developed a compact vacuum X-ray tube using an alumina body instead of glass. A filament is implanted as a cathode which follows Richardson-Dushman equation. After aging the filament to eliminate impurities on the filament which improves performance of filament before tubing, tube current was obtained from anode voltage of 6kV, 3mA to 40kV, 3.15mA. The pulse high voltage generator is designed and developed to make the tube less stressful. With the ceramic X-ray tube, X-ray images of human breast and teeth phantom were successfully obtained, verifying the potential of the compact alumina vacuum sealed X-ray tube in X-ray application for medical imaging.
We designed and developed the vacuum sealed x-ray tube based on carbon nanotube(CNT) field emitter for mobile medical x-ray devices and also design the test bed for CNT x-ray tube. The CNT was synthesized by chemical vapor deposition(CVD) method on a metal alloy substrate. The grown CNT is assembled with a gate and a focuser and then combined into an electron gun(e-gun) through a brazing process. The the e-gun had an aging process inside the vacuum chamber. As a result of aging, the CNT e-gun was able to generate anode current of 1.5 mA at electric field of about 4 V/μm, and field emission current was also stabilized. After the aging process, the e-gun was brazed into a ceramic X-ray tube inside a high-temperature furnace at a vacuum degree of E-06 torr and vacuum sealed. Field emission characteristic was measured using this X-ray tube and compared with an e-gun, and almost similar results were obtained. Incase of Xray tube, we applied a higher electric field while controlling the current at 500ms intervals through pulse driving. As a result, X-ray images of human teeth were successfully acquired using CNT X-ray tubes.
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