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RESEARCH PRODUCT

Depth profiles of hardening in lithium fluoride irradiated with swift58Ni ions

subject

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The changes of hardness and dislocation formation in LiF crystals irradiated with 630-MeV 58Ni ions up to a dose of 20 MGy were studied by microindentation and dislocation etching techniques. Above the threshold fluence of 2 × 1010 ions/cm2, a marked effect of hardening, which is related mainly to damage processes in the track core, has been observed. Its magnitude depends on ion fluence and energy loss. To investigate the depth distribution of hardening, indentation tests on crystal cross sections cleaved parallel to ion flux were performed. It has been found that the hardness change along the ion path correlates with the ion energy loss and reaches the highest value at the Bragg maximum. Significant internal and long-range stresses are generated in crystals due to the volume expansion of the irradiated layer. Formation of dislocations on the irradiated surface is observed. At high-fluence irradiations, the relaxation of stresses by generation and glide of dislocations in the adjacent non-irradiated crystal is observed and an additional increase in hardness due to the effect of work hardening was found to occur. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)