Energy Loss Measurements in the Pep Tpc*

The PEP TPC' is a cylinder two meters long with a radius of one meter filled with argon mixed with 20% methane. The TPC can operate at pressures from one to 10 atmospheres. When a particle traverses the TPC, the electrons liberated by ionization drift parallel to the cylinder axis (z-axis) at about 5 cm per microsecond. lhe detector plane at each end is divided into six sectors, each of which has 183 detection wires, as shown in Fig. 1. The pulse heights from these wires are used to measure the track ionization. In each sector on the end plane there are 15 rows of pads. The pad spacing is 7.5 mm. The data from these pads provide three dimensional measurements of the track position. For both the pads and the wires a z-position is calculated from the drift time. For the pads an aximuthal position is calculated from the pad pulse heights.