Reduction of the X-ray level of DC ion accelerators

In order to reduce the X-ray intensity level of a 2 MV dc ion accelerator, the accelerating tube is equipped with a system of permanent magnets. The transversely directed magnetic fields sweep secondary electrons sideways into the electrodes of the accelerating tube before they have gained a high energy. Computer simulations show that the maximum electron energy is reduced to roughly 140 keV; the X-rays produced are absorbed by the 2.5 cm thick steel wall of the high-pressure vessel. Continuous X-ray monitors indicate that the dose-rate equivalent at 10 cm outside the accelerator vessel does not exceed 0.1 mrem/h, when the accelerated H+-ion beam current is 100 μA. The magnetic field can be designed such that the ion beam is on axis on leaving the accelerating tube, irrespective of the ion mass and energy. (orig.)