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Very Compact High Performance Microchannel Plate Thermal Neutron Collimators



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IEEE Nuclear Science Symposium and Medical Imaging Conference Portland Oregon October 2003 1 Very Compact High Performance Microchannel Plate Thermal Neutron Collimators Anton S Tremsin David F R Mildner W Bruce Feller R Gregory Downing Abstract In most neutron scattering experiments and in boron neutron capture therapy the angular spread of the neutron beam is defined by the quality of the neutron collimator A typical collimator consists of a large number of parallel plates coated with neutron absorbing material and at present these plates are at least few centimeters in length In order to obtain collimation in both vertical and horizontal planes two orthogonally aligned collimators are installed in the neutron beam We present a new type of high performance neutron collimator made with Gd doped microchannel plates MCPs Such collimators are only few millimeters thick and the rocking curve is expected to be even sharper than that of conventional 0 5o collimators While collimation is performed in two perpendicular planes simultaneously the geometry of these new collimators can be changed so that the degree of collimation in each direction is controlled independently The modeling of the proposed collimator indicates that for the existing MCP technology the rocking curve can be made as sharp as 0 2o FWHM which can be further improved by current developments in the MCP technology The preliminary experimental evaluation of our first very thin only 0 6 mm MCP collimators confirms the accuracy of our numerical model Index Terms Neutron optics collimators I INTRODUCTION neutron beams are usually collimated with a Thermal Soller slit collimator comprising an array of absorbing films separated by neutron transparent spacers Currently produced collimators use stacked arrays of stretched polyethylene films or thin single crystal silicon wafers with absorbing coatings 1 3 The thickness of the spacers and the absorbing coatings are optimized in order to achieve high degree



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