Two-dimensional position-sensitive proportional chamber using weighted coupling capacitor read-out

The chamber has two parallel cathode planes and a multi-wire anode, the latter being placed at the mid-plane of the former. One of the cathodes is split into a number of strips at right angles to the anode wires to yield position information (Y-coordinate) perpendicular to the one obtained from the anode (X-coordinate). Each anode wire is connected to two charge sensitive amplifiers through coupling capacitors, the capacities of which are weighted according to the position of the wire; that is, the i-th anode wire from one end is coupled to amplifiers A1 and A2 through capacities Csub(1i) and Csub(2i), respectively, given by the following equations, Csub(1i)=Csub(x).i/(n+1) and Csub(2i)=Csub(x).(n+1-i)/(n+1), where n is the total number of the anode wires and Csub(x) is the constant capacity. The set of Csub(1i) and Csub(2i) was formed by etching an epoxy print-circuit plate. The position signal is given by V1/(V1+V2), where V1 and V2 are the outputs of the amplifiers. A pulse ratio circuit is used to perform the calculation, when the energy signal, V1+V2 passes a single channel pulse-height analyzer. The read-out of the Y-position signal is performed similarly from the cathode strips. Performance of the system was tested using 5.9 keV x-rays from a 55Fe source. The position resolution along the X-axis was restricted by the spacing of the anode wires, 3mm, because most of the electron avalanches occur mainly near only one wire. The resolution along Y-axis was, however, not limited by the width of the cathode strips, 5mm, and was far better than this. (JPN)