Moessbauer effect investigation of the vibrational behaviour of interstitials trapped at 57Co impurities in aluminium

The temperature dependence of the Debye-Waller factor of highly dilute 57Co in aluminium was measured, before as well as after fast neutron irradiation at 4.6K. After irradiation at 4.6K followed by an annealing treatment up to temperatures between 35 and 160K, there appeared an additional Mossbauer line due to irradiation induced aluminium interstitials trapped at the 57Co impurities. The temperature dependence of the Debye Waller factor of the additional line is much stronger than that of the original line indicating the appearance of low frequency vibration modes of the impurity-interstitial complex.