Abstract: An ionization chamber for measuring the profile of a radiation field is provided which comprises a first electrode and a second electrode arranged parallel to said first electrode, both electrodes forming a gap therebetween. A shield made of a material opaque to ions produced by the radiation field is movably arranged in said gap between said electrodes and has an aperture, which between said electrodes forms a measuring volume. The ionization chamber further comprises means for moving said shield together with said aperture along said gap between said electrodes.

Abstract: The particle accelerator contains an accelerator guide for accelerating particles, an injector for injecting particles into the accelerator guide, a pulsed source of high frequency power which has power adjusting means, a device for introducing the high frequency power from the source into the accelerator guide, a measuring device for measuring particle pulses emitted from the accelerator guide, and a power control circuit connected to the power adjusting means. The power control circuit includes a circuit for supplying an adjusting signal in dependence on the deviation of each particle pulse from an optimum pulse form and a connecting circuitry for connecting the adjusting signal to the power adjusting means. By changing the high frequency power of the source, the form of the measured particle pulses is adjusted towards the optimum pulse form.