Timing resolution and detection efficiency of the St. George detector system

The St. George recoil mass separator at the University of Notre Dame will be used to study $(\alpha , \gamma)$ reactions of astrophysical interest. A detection system was developed for the St. George recoil mass separator by Indiana University South Bend that will utilize energy and time-of-flight to separate reaction products from residual unreacted beam particles. The detection system utilizes two transmission detectors in which secondary electrons produced by the passage of an ion through a thin foil are deflected by electric and magnetic fields onto a microchannel plate (MCP) detector, which registers timing measurements. A silicon strip detector is used to measure the ion's kinetic energy. Measurements were conducted with an alpha source of Am-241 and Gd-148 to determine the MCP efficiency and timing resolution. The best values achieved to date are 75\% for efficiency and 550 ps for timing resolution. The program SIMION was used to investigate further the effect of varying the voltages applied to the foil, the field-shaping electrodes, and the MCP detector, on the efficiency and timing resolution.