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An evaluation of the precision and accuracy with which sharp electron diffraction rings may be measured and d values may be calculated is given. Using an evaporated aluminum specimen and the high-resolution diffraction attachment of a Hitachi HU-11 microscope, a maximum measurement precision of about ±0.005 mm at 95 per cent confidence limits may be attained for a given diffraction ring on a single plate. For the experimental conditions used, and at about 1.8 deg θ, this corresponds to a precision of ±0.0002 deg θ, and ±0.01 per cent of d. Accuracy is usually less than this by a factor of at least 2 or 3. The major factor affecting accuracy was found to be variations in stray, inhomogeneons magnetic fields between the specimen and the plate. These variations cause minute-by-minute variations in diffraction ring circularity of two or three times the measurement precision level. Taking these and other factors into account, recommendations are made for evaluating the maximum practical precision and accuracy in electron diffraction d value data in terms of round-robin samples.
Beu, Karl E.
Goodyear Atomic Corp., a subsidiary of The Goodyear Tire and Rubber Co., Portsmouth, Ohio