THERMAL-NEUTRON IMAGING DETECTORS COMBINING NOVEL COMPOSITE FOIL CONVERTERS AND GASEOUS ELECTRON MULTIPLIERS

The potential of a thermal neutron imaging system based on a composite neutron convertor foil combined with a low-pressure, multistep avalan che chamber is demonstrated. Neutron-induced charged particles from a primary convertor element induce multiple low-energy electrons escapin g from a second thin film of high electron-emissive material. We inves tigated the performance of detectors with Gd- and Li-based primary con vertors coated with CsI as a secondary electron emitter. It is shown, that the detector can be operated with high stability at a sufficientl y high gain to detect all escaping particles. A localisation resolutio n of 0.4 mm (fwhm) was obtained. With Li-based convertors a very low g amma-ray sensitivity was established. The good imaging performance, fr ee of parallax errors in divergent neutron beams, fast time resolution , low occupation time and high count rate capability, make this instru ment an excellent tool for time-resolved neutron scattering experiment s and for neutron radiography and tomography.