<title>High-speed soft x-ray generators in biomedicine</title>

Abstract

The constructions and the fundamental studies of high-speed soft x-ray generators which can be used for performing biomedical radiography with maximum photon energies of less than 150 keV are described. The flash x- ray generators having cold-cathode radiation tubes are classified to four types: (1) high-intensity single flash x-ray generators, (2) dual- energy flash x-ray generators, (3) single plasma flash x-ray generators, and (4) repetitive compact flash x-ray generators. In general, when we employed flash x-ray generators with diodes, the pulse widths had values of less than 200 ns. In the case where we employed a long-duration flash x-ray generator having a triode, the width could be increased up to about 40 microsecond(s) . The maximum tube currents achieved with high-intensity generators were more than 10 kA, and the maximum repetition rate of a compact generator has a value of about 0.4 kHz. In order to obtain higher repetition rates of more than 1 kHz, we developed three types of pulsed x-ray generators having hot-cathode tubes as follows: (5) a 30 kHz high-dose-rate generator, (6) a 30 kHz variable-duration microsecond generator, and (7) two 10 kHz high-photon-energy generators. When a high-dose-rate generator was employed, the maximum tube current can be increased up to about 2 A by applying the positive grid voltage. In contrast, as the duration was controlled in a microsecond range by using a microsecond generator, the sufficient x-ray intensities for the normal radiography were obtained. The maximum photon energy could be increased more than 100 keV using a high-voltage transformer in conjunction with a diode. Using these generators, we performed various kinds of high- speed soft radiographies.