Linear accelerator x-ray sources with high duty cycle

X-ray cargo inspection systems typically use a several-MV pulsed linear accelerator (linac) to produce a bremsstrahlung spectrum of x rays by bombarding a target with electrons. The x rays traverse the cargo and are detected by a detector array. Spectroscopy of the detected x rays is very desirable: if one can determine the spectrum of the transmitted x rays, one can determine the Z of the material they traversed. Even in relatively low-dose modes of operation, thousands of x rays arrive at each detector element during each pulse, unless the x rays are heavily absorbed or scattered by the cargo. For portal or fixed-site systems, dose rates, and therefore x-ray count rates, are even higher. Because of the high x-ray count rate, spectroscopy is impractical in conventional cargo inspection systems, except in certain special cases. For a mobile system, typical pulse durations are a few microseconds, and the number of pulses is on the order of 100 per second, leading to a duty factor of about 0.04%. Clearly, a...