A
detector for detection of
ionizing radiation, an apparatus for use in planar beam
radiography, comprising such a
detector, and a method for detecting
ionizing radiation. The
detector includes a chamber filled with an ionizable medium, at least one first
electrode arrangement provided in said chamber where said at least one first
electrode arrangement includes an
electron avalanche amplification unit, said
electron avalanche amplification unit including at least one avalanche
cathode and at least one avalanche
anode between which a
voltage is to be applied for creation of an
electric field for avalanche amplification, and at least one arrangement of read-out elements for detection of
electron avalanches, wherein said at least one avalanche
cathode has at least one hole or opening, wherein an area of said at least one hole or opening in the avalanche
cathode is bigger than an area of at least one associated
anode as seen from above and where said at least one
anode is centered with respect to said at least one hole or opening in the avalanche cathode. A
radiation entrance is provided so that
radiation enters the conversion volume between the first and second
electrode arrangements. In order to achieve well-defined avalanches, the
electron avalanche amplification unit includes avalanche regions. The detector, apparatus and method is advantageous since it prevents the formation of harmful sparks.