Daresbury Recoil Separator
Focal Plane Detector Systems

The MCP detector uses a large-area (7 cm diameter) carbon foil, an acceleration grid, a microchannel plate, and a two-dimensional position-sensitive anode to derive fast timing (to less than 1 ns precision) and position (to less than 1 mm precision) information on incident recoils. The detector assembly is mounted so that the carbon foil intercepts the beam at a 45 degree angle. The system can be retracted out of the beam path without breaking vacuum. A schematic diagram of the detector illustrates its operating principle.

The Ionization Counter has a very thin (50 ug/cm2) polypropylene window, a cathode, a Frisch grid, and a three-segment anode structure. The detector typically operates with 20 Torr of Isobutane gas. The three anode segments (of lengths 50, 50, and 200 mm) allow two energy-loss measurements and one residual energy measurement, respectively, of the incident recoils. The energy loss and residual energy information are used to identify the nuclear charge of the recoils, and the two energy loss measurements are used to reject events in which recoils scatter off detector gas molecules. The window assembly includes a biased grid of thin wires which keeps the entrance window flat under pressure and which maintains an even electric field gradient near the detector entrance. A schematic diagram of the detector illustrates its operating principle.