Position sensitive detection of thermal neutrons by Gd-Si-planardiodes

Recent advances in the technology of position sensitive silicon detectors and the corresponding electronics allow the construction of fast time response thermal neutron detectors. These detectors also exhibit excellent position resolution and good efficiency by combination of Silicon sensors with Gadolinium converter foils. The neutron detection is based on the (n,y) reaction in Gd which produces a quite complex conversion electron spectra with significant energy lines between 29 keV and about 200 keV, which can be detected in the Si sensors. Due to the high absorption cross section of Gd the converter can be made very thin. Hence the range of the conversion electrons is sufficient to reach the Si-sensor. This thin converter together with the short charge collection time in Si ensures the good time resolution of the device. We constructed several one- and two-dimensional prototype detectors, using DC and AC coupled silicon strip detectors, pad detectors and different VLSI readout electronics. The position resolution and the detector efficiency were determined for converters made of natural Gadolinium and 90.5 % enriched sup 1 sup 5 sup 7 Gd at wavelengths from 1.1 A to 3.3 A at the TRIGA reactor in Vienna and at the ILL in Grenoble. Spatial resolutions of less than 100 pm and efficiencies up to 40 % have been achieved. The results of these measurements are compared with a simple calculation of the detector operation