Radiation detector, an apparatus for use in planar beam radiography and a method for detecting ionizing radiation

A detector for planar beam radiography having a chamber filled with an ionizable gas in which the production of electron-ion pairs take place and a radiation entrance, the detector comprising;

• first and second electrode arrangements located within the chamber, spaced apart such that a first portion of the space therebetween acts as a conversion and drift volume, the height of which is considerably less than 1 mm, and a second portion acts as two or more electron avalanche amplification units, wherein the radiation entrance permits radiation, including electrons, to enter the conversion and drift volume parallel to the first and second electrode arrangements;
• said two or more electron avalanche amplification units include each at least one avalanche cathode and at least one avalanche anode, between which a voltage can be applied to create an electric field in the vicinity of each of a plurality of avalanche regions formed by an arrangement of said at least one avalanche cathode and said at least one avalanche anode and each of the electron avalanche amplification units includes field concentrating means;
• and
• at least one arrangement of read-out elements for detecting electron avalanches in the plurality of avalanche regions.