THE PARALLEL-PLATE AVALANCHE COUNTER - A SIMPLE, RUGGED, IMAGING X-RAY COUNTER

A two-dimensional parallel gap proportional counter has been developed at the Danish Space Research Institute. Imaging over the 120 mm diame ter active area is obtained using the positive ion component of the av alanche signals as recorded by a system of wedge- and strip-electrodes , An electronically simple, but very effective background rejection is obtained by using the fast electron component of the avalanche signal . Gas gains up to 8 x 10(5) have been achieved. An energy-resolution o f 16% and a sub-millimeter spatial resolution have been measured at 5. 9 keV for an operating gas gain of 10(5). In principle, the position c oordinates are linear functions of electronic readouts. The present mo del, however, exhibits non-linearities, caused by imperfections in the wedge and strip-electrode pattern. These non-linearities are correcte d by using a bilinear correction algorithm. We conclude that the rugge d construction, the simple electronics, the effectiveness of the backg round rejection and the actual imaging performance makes this a very a ttractive laboratory detector for low and intermediate count rate imag ing applications.