The value of the atomic form factor, /(220), for copper has been determined in recent years by a variety of methods. All the dynamical methods agree on a value in the region of 16'70-16�75. These methods include two X-ray methods, one involving measurement of intensity profiles and the other of Pendellosung beats, and also an electron diffraction measurement using a critical voltage procedure. By contrast, two recent kinematical measurements using y rays both report a distinctly different value of about 16�45. One of these determinations has already been re-examined by the present authors and the iscrepancy removed by an appropriate extrapolation to zero extinction.
Isomorphism in the model compounds of liquid-crystalline arylate polymers as confirmed by electron diffraction measurement.