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X-rays entering through the aluminum window in teract with the pressurized gas (xenon) in region A. The resulting ions are impelled to the detection region by a drift field of 1000 volts/cm. In the detection region are mounted three parallel wire planes: two outer planes being operated at ground potential (cathodes), with the inner plane at high positive potential (anode). The drifted ionization is collected at the anode, where the charge is amplified by gas avalanche. Position determination of the anode avalanche isob tamed by detection of the signals induced in the two cathode grids, which are oriented orthogonally to each other. Each wire of each cathode grid is attached to a tap of a discrete delay line, and position is sensed by mea surement of the delay time between occurrence of the avalanche on the anode grid and arrival of the signals at the ends of the cathode delay lines. Unlike previously reported delay-line …