TARGETS FOR THE APEX EXPERIMENT AT ATLAS

Targets of lead, tantalum, thorium and uranium have been produced for experiments with the APEX (Argonne Positron Experiment) apparatus at A TLAS (Argonne Tandem Linac Accelerator System). APEX is a device built at Argonne National Laboratory to investigate the anomalous positrons observed in collisions of very heavy ion beams on heavy targets. Both fixed and rotating targets have been used. The rotating target system involves a 4-quadrant wheel rotating at speeds up to 750 rpm with the position encoded into the data stream. In addition to the hundreds of targets produced for the heavy-ion reactions studied, a wide variety of targets were employed for beam diagnostics, detector calibration an d target wheel development. The experiment used very heavy ion beams ( U-238, Pb-206 and Pb-208) from ATLAS and targets of Pb-206, Pb-208, Th -232 and U-238 produced in our laboratory.