NOVEL LARGE-AREA THERMAL-NEUTRON IMAGING DETECTORS COMPRISING GD-157 CSI-CONVERTERS AND MICRO-STRIP GAS DETECTORS WITH LOW-PRESSURE, 2-STAGE AMPLIFICATION AND DELAY-LINE READOUT/

A novel large-area (0.5 x 0.5 m(2)) two-dimensional position-sensitive detector for thermal and sub-thermal neutrons is being developed comp rising Gd-157/CsI multilayer convertor foils and two fourfold segmente d micro-strip gas detector (MSGC) planes for electron multiplication o n either side of the convertor. The MSGC operates in low-pressure, two -stage amplification mode; their novel design is optimized for that mo de and for obtaining high signals on both coordinates. Fast signal ris e times (5-6 ns) and very high gains (similar to 5 x 10(5)) are expect ed according to calculations; thus, simple delay line readout, with on e interpolating strip between readout nodes, can be used delivering ex pected position resolutions < 0.5 mm (fwhm) and tolerable count rates of 10(5)-10(6) events/s depending on delay line segmentation.