Acoustic and photon emissions during mechanical deformation of coloured alkali halide crystals

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Abstract
Acoustic and photon emissions take place in the elastic and plastic as well as the fracture region of X-irradiated KBr, KCl and NaCl crystals. The rate of photon emission is linear with the strain rate: however, the RMS value of the acoustic emission is proportional to the square root of the strain rate. The acoustic emission is maximum for X-irradiated NaCl crystals; however, the photon emission is maximum for X-irradiated KBr crystals. From the similarity between the acoustic emission and the photon emission, it seems that mobile dislocations are responsible for the acoustic emission in coloured alkali halide crystals. It is concluded that similarly to the acoustic emission, photon emission measurements may also be useful in non-destructive testing of materials. For materials which do not emit photons, to emit less photons during their deformation, a coating of a thin film of an intense mechanoluminescent phosphor on the materials may be helpful.