Neutron polarisation and polarisation analysis with 10-4 accuracy and design of the beam line for PERC

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PERC and other projects investigating correlations in neutron beta decay are presently limited in accuracy at the 10-3 level by the knowledge of the average neutron beam polarisation. In this project, techniques for the polarisation of a roughly monochromatic (∆λ/λ about 10%) cold neutron beam will be pushed towards the 10-4 level. This includes developing and testing optimised super mirror polarisers and neutron spin flippers capable of working in high magnetic fields as well as challenging the limits of polarisation analysis using 3He neutron spin filters. It is expected that the attempted level of precision in polarisation can only be obtained in an optimised design of the full beam line, including polarisation analysis. This is the final goal of this project, for the new instrument PERC, and comprises also the optimisation of beam shaping components as neutron velocity selector and chopper system and of neutron spin transport.