Abstract
An alpha irradiation device is described that utilises a commercially available disc-shaped americium-241 source of 8 cm diameter. The alpha particles traverse a moving collimator and the source is rotated to reduce the influence of source inhomogeneities. Source, collimator and a shutter disc are mounted in a container which is flushed with helium to reduce energy losses of the alpha particles before reaching the exit foil. The shutter disc is activated by a computer-controlled step motor. The broad beam of alpha particles emerges from the exit window of the container with a remaining range in tissue of about 15 mu m. An intermittent computer-controlled use of a preabsorber makes it possible to reduce dose differences within a depth up to 12.5 mu m to not more than +or-3%. With the commercially available americium sources a dose rate of 0.2 Gy min-1 is reached; this can be increased by utilising a somewhat wider collimator.