A microchannel plate system for accelerator mass spectrometry measurements

The position-sensitive focal plane detector system for the trace element accelerator mass spectrometer at the US Naval Research Laboratory consists of 12 microchannel plate detector modules. Each module provides a 10×2 cm2 active area and together they cover 80% of the split-pole spectrograph focal plane. The MCP detects electrons produced when an MeV ion beam passes through a thin carbon foil placed at 45° with respect to the beam. The electric charge is amplified and deposited on a double-delay line anode, with differential timing at the two ends providing horizontal position. Vertical position is evaluated from top-to-bottom charge partitioning. The collected charge is converted to timing signals through specially designed readout electronics based on the MQT300A LeCroy integrated circuit. A 400-μm horizontal resolution was obtained from ion beam generated secondary electrons accelerated to 2.5 keV. A Helmholtz-type coil pair was built for further confining the secondary electrons with a magnetic field.