Vol.2 No.3 2009

Research paper : Development of battery-operated portable high-energy X-ray sources (R. Suzuki)−223−Synthesiology - English edition Vol.2 No.3 (2009) Figure 4 is an X-ray transmission image shot by supplying 20 J power to the high voltage generating circuit. The LSI chips in the laptop PC can be photographed at resolutions of 0.2 mm or less. Also, the electrodes in the ceramic insulator about 10 cm in diameter can be seen clearly. With energy of about 20 J, high-resolution X-ray transmission images of various objects can be photographed well for practical purposes. It was confirmed that when X-ray transmission images were photographed at energy of 20 J per shot, over 100 shots could be taken using one AA size nickel metal hydride battery (capacity: 2000 mAh), or over 300 shots with two batteries. The X-ray tube did not show deterioration after X-ray generation for 106 shots at 50 J energy per shot. It was confirmed that it can be used as a portable X-ray source without problem.Moreover, the maximum emission current of this X-ray tube was 50 mA or higher, and X-rays with high output could be generated in a short time. This allows short-time exposure of 1 millisecond or less. Using this high output property, it can be used as an X-ray tube for computer tomography (CT) that requires high output X-rays, as well as for ordinary X-ray transmission image photography.If the X-ray source technology is likened to a radio, the conventional X-ray source is a vacuum tube radio where one has to mind the battery all the time when carrying it around, while the carbon nanostructure X-ray source is equivalent to a transistor radio, and the portability of the X-ray source increases dramatically. This will allow nondestructive evaluation and diagnosis by X-rays to be done easily on site, and new innovations in X-ray evaluation can be expected.3 Circumstances leading to achievement of the resultsThe author et al. have been involved in the development and practical application of the electron accelerators, and the development of the new X-ray source described in chapter 2 was realized by fusing the portable ultra-small accelerator and X-ray source technology of AIST and the carbon nanostructure electron source technology developed by companies. Moreover, the technologies for ultra-small accelerators and X-ray sources were based on the technologies for energy saving and downsizing of the electron accelerator. The elemental technologies that became the basis of the development of a new X-ray source are described as follows.3.1 Energy saving in electron accelerator facilityThe author et al. have been involved in the management, operation, and research using the S-band electron linac (linear accelerator) with maximum energy 400 MeV at AIST. This accelerator was completed in 1979, and has been used as the electron storage ring TERAS for synchrotron radiation, the electron storage ring NIJI-IV for free electron laser, the high-intensity slow positron beam source for material evaluation experiments, and others[2]. Energy-saving measures were conducted for the entire accelerator facility when the aged air conditioning system was renovated in FY 2005.Before the energy-saving measures were executed, the power consumed when the electron linac was in operation momentarily reached 600 kW, and the annual amount of power used was about 2.5 GWh or more. Estimating the electron linac beam power truly needed during electron injection to the storage ring, it was only 0.01 % of the power consumed when the accelerator was actually in operation, at 320 (MeV) × 100 (mA) × 1 (µs) × 2(pps) = 64 (W). In case of the positron experiment, it was 70 (MeV) × 100 (mA) × 1 (µs) × 100 (pps) = 700 (W) or several hundredth of the actual power consumed.There were several factors for this extremely low efficiency. The major factor was because originally, the air conditioning and water heating/cooling systems for this electron linac and the accompanying facilities were designed for generation of high-output electron beams of several 10 kW in order to handle various experiments. Therefore, they were not optimized for low-energy modes such as the positron experiment or low pulse rate modes such as injection to electron storage rings.To solve this issue, total measures were necessary for the electron linac itself as well as its air conditioning and water cooling/heating systems. Therefore, energy-saving measures were considered by combining the accelerator technology accumulated over time and the latest technology for air conditioning, water cooling/heating, and power source systems. In executing these energy-saving measures, the following basic principles were set.1. Energy is used only for the amount it is needed.Fig. 4 X-ray transmission image with input power 20 J.(Left) X-ray transmission image of laptop PC.(Right) X-ray transmission image of alumina insulator with test electrode.10 cm


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