The Lead/Liquid Argon Shower Counter Systems of the Spear Mark II Detector

The electromagnetic shower detection system of the Mark II Magnetic Detector consists of ten large lead/liquid argon modules. Eight of these, termed "barrel" modules, are placed outside the aluminum coil which defines the magnetic field volume of the device. The other two, the "end-cap" modules are placed at the ends of the solenoid. The design and construction of the lead assemblies, the tank structure and the cryogenic system will be described, as will the data acquisition electronics. Preliminary results on the performance of the first barrel module will be presented.