A NEW SOLUTION TO THE PHASE PROBLEM. Gu Xu, Dept. of Materials Sci. & Eng., McMaster University, Hamilton, Ontario, L8S 4L7, Canada

A new solution is proposed to solve the 'phase problem', which has in the past prevented people from using X-rays to determine non-crystalline structure, and made phase determination tedious, if not impossible, for bio-molecular crystals. It involves only current X-ray diffraction technology, with the sample attached to a single crystal to form an assembly. The X-ray intensity diffracted by the assembly will then produce a convolution function which contains the cross modulation of both the unknown and crystal density functions. With the known crystal structure, the electron density of the amorphous or biological specimen can thus be resolved by a simple mathematical image inversion algorithm to obtain the atomic arrangements in 1, 2 or 3 dimensions. In principle, this method uses the same idea of a reference object of known structure (the single crystal) to probe the unknown, as the holographic method now widely used in optical systems. However, no reference beam is needed in this method, thus no macroscopic coherent X-ray is necessary. Moreover, the Bragg diffraction peaks from the single crystal can be omitted from the measurement, which provides the scheme with the same noise tolerance as used in the usual amorphous diffraction experiment.