The Diffraction Pattern of Cold Worked Metals: I The Nature of Extinction

The influence of crystal perfection on extinction is briefly discussed and the possible corrections given. Experimental results for chemically produced copper and annealed aluminium filings have been obtained with a Geiger counter spectrometer using monochromatic radiation. The intensity measurements, and for copper the experimentally determined particle size, were inconsistent with the views that primary extinction occurred, but could be interpreted wholly in terms of secondary extinction, the corrected f values agreeing within ±2% with accepted values. Evidence to show that annealed metals contain residual lattice strain is advanced, in accord with the dislocation theory, and it is suggested that secondary extinction will predominate over primary extinction in all crystals containing such dislocations.