The Phase Problem in Neutron Crystallography

With ND the former condition fails when hydrogen atoms are present, J. Karle and I. Karle, Acta Cryst., 1966, 21, 849. 

As with Af-ray data, the phase problem becomes much harder when the structure is acentric, so that each phase-angle might have any value between 0 and 2jt. Even if we are prepared to simplify the problem by asking for angles, for N structure amplitudes, that are within the correct quadrant (0 - 5 - re, re - - 2re), we have to find the correct one out of 4 sets 

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