A 2 dimensional GMSD based imaging detector for neutrons

The development and testing of a 2-D prototype detector based on a gas microstrip detector (GMSD) is reported using a gas mixture of 2.5 bar ³He and 2.5 bar CF₄. The second coordinate is obtained by utilising a plane of wires as pick up electrodes. The detector is operated with the wire plane at such a potential so as not to induce any gain around the wires. This means that the high tolerances normally associated with wire planes in multi wire proportional counters are not mandatory. The detector comprises of 48 individually instrumented channels in both X (GMSD strips) and Y (transverse wire plane). A specially designed encoding module has been constructed which feeds digital addresses for each event to the ISIS data taking electronics system (DAE). An intrinsic detector resolution of ∼1 mm FWHM has been measured for both dimensions (in experimental exposures on the ROTAX beamline at ISIS) which is degraded slightly by the digital resolution for the overall system. This readout method is shown to be very tolerant of a poor signal to noise ratio in the readout channels (unlike traditional analogue wire chamber readout systems) and permits the operation of the GMSD at low avalanche gains (∼10) which helps to maximise the rate and lifetime performance of the detector as well as permitting data capture rates in the MHz range. The event timing resolution is comfortably sub microsecond and is therefore suitable for applications on spallation neutron sources.