Abstract
A simple read-out method of position signals for a two-dimensional proportional chamber has been investigated. 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 C1i and C2i, respectively, given by the following equations, C1i=Cx⋅i/ (n+1) and C2i=Cx⋅ (n+1-i) / (n+1), where n is the total number of the anode wires and Cx is the constant capacity. The set of C1i and C2i 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 5.9keV X-rays from a 55Fe source. The position resolution along the X-axis was restricted by the spacing of the anode wires, 3 mm, 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, 5 mm, and was far better than this. The reason for this is that the movement of positive ions toward the cathode strips induces signals on a number of the strips near the avalanche and an interpolation effect expected.
