SU-E-T-79: Fabrication of Miniature X-Ray Tube Using Carbon Nanotube Field Emitter for Electronic Brachytherapy

Abstract

Purpose: A miniature x‐ray tube with the diameter of 10 mm has been fabricated using a carbon nanotube(CNT)field emitter, optimal design of electron optics and x‐ray target, and vacuum sealing of the x‐ray tube. The CNT emitter with nm∼μm scale and simpler cathode structure was used for miniaturization of x‐ray tube. A truncated conical shaped beryllium (Be) and thin tungsten (W) coating were adopted to emit 3‐dimensionally uniform x‐ray as an isotropic radiation source. Anode grounded high voltage (HV) connection and vacuum sealed x‐ray tube structure within 10 mm diameter are advantages for intra‐cavitary or skin surface electronic brachytherapy. Methods: The miniature x‐ray tube consisted with a tip‐shaped CNT emitter with the diameter of 0.25∼0.8 mm, a focusing electrode, a transmission‐type x‐ray target, getter film and a metalized HV isolation ceramic. The CNT emitter has been fabricated by coating and sintering of CNT and Silver nano particle mixture on the flat W tip. The miniature x‐ray tube is brazed in a 3×10−6 torr of vacuum furnace. The electron and x‐ray emission are calculated by EGN2 and MCNP5 program, and measure using a precision current meter (Fluke multimeter 189), a soft x‐ray chamber (PTW 34013), and x‐ray spectrometer (Amptek XR‐100t‐CdTe). Results: The CNT emitter emitted electron current over 1 mA at −9.8 kV/5 mm, and 0.1 mA was continued for over 3000 minutes with decrease ratio of −0.01 μA/min. The diode‐type miniature x‐ray tube is started to emit less than 5 Gy/min x‐ray at cm air depth from −20 kV to −50 kV following the gate to CNTcathode gap, and applying cathode voltage. Conclusions: The miniature x‐ray tube using CNTfield emitter has been demonstrated. The CNT based x‐ray tube can be more miniature, and is expected to apply various field of electronic brachytherapy, soon. This work was supported by the R&D Program of MKE/KEIT (10035553, Development of multi‐direction X‐ray emitting super‐miniature X‐ray tube for intra‐cavity imaging system) and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2010‐0020387).