THE RAPID HIGH-RATE LARGE-AREA X-RAY-DETECTOR SYSTEM

The multiwire proportional counter (MWPC) is a well-established device for capturing X-ray images from synchrotron sources and is particular ly well suited to dynamic experiments. Its advantages include, almost zero noise, high dynamic range limited only by the electronic memory d epth, large area and time resolutions of microseconds. It does however have some limitations, notably in global and local count rate perform ance. The RAPID two-dimensional detector system delivers a more than t wentyfold increase in throughput over present systems. It comprises a ''wire MicroGap'' detector, which has much higher count rate performan ce than coventional MWPCs and a sophisticated multi-channel data acqui sition system. The system has a global count rate capability of greate r than 2 x 10(7) photons s(-1) with a maximum local count rate of simi lar to 10(6) photons mm(-2) s(-1). A spatial resolution of similar to 200 mu m, over an active area of 12.8 x 12.8 cm, has been achieved whi ch compares well with exiting read-out systems. Each electrode of the detector is instrumented with a preamplifier and ADC and the position of the event is determined independently in X and Y by centroiding the induced charge distribution. The X and Y coordinates are correlated u sing a unique time stamp. This paper described the design and performa nce of the detector and read-out system and presents some recent beaml ine results.