Plate ionisation chamber has alternating signal and voltage electrodes - of open lattice structure slightly domed for stiffness

摘要

A plate ionisation chamber for beta and soft gamma radiation comprises a number of rotationally symmetrical potential and signal electrodes arranged one behind another. The potential electrodes and the signal electrodes are made of thin foil, with large portions cut away to leave a lattice or grating structure; these electrodes are stabilised by deforming them, more specifically by a flat dome shape. The electrodes may be produced by a mould etching process. A signal electrode is composed of rings and radial webs; the voltage electrode has a similar pattern but the webs of voltage and signal electrodes are staggered relative to each other to improve the homogeneity of the field strength. In addition, the active chamber volume may be separated from dead space by peripheral collars or flanges integrally formed on the signal electrodes around their perimeter. The homogeneity is improved by having electrodes with comparatively large open areas but without the difficulty of applying a large number of bores to a plate. Manufacture is inexpensive and simple.