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[en] Moessbauer effect measurements are reported with sources of ¹³³Xe implanted in Mo, W and Ta by means of the Leuven Isotope Separator. Information about the direct environment of an implanted radioactive probe atom is obtained through the hyperfine interaction of the daughter nucleus (¹³³Cs) with its surroundings. Each of the sources is subjected to an isochronal annealing sequence in order to study the recovery of each metal. For Mo and W four visible components are detected in the Mossbauer spectra. Identification of the components on the basis of their Moessbauer parameters shows that the components represent substitutional xenon atoms and xenon atoms associated with one, two and three vacancies. The observed population of the visible sites leads to the necessity of the existence of at least one type of 'invisible' site with a recoilless fraction very close to zero. Vacancy trapping at xenon impurities occurs in Mo around 425 K and in W around 550 K. It is shown that the associated vacancy migration is largely a free migration, indicating that recovery stage III in Mo and W is due to vacancy migration. The free-vacancy migration in Mo and W is shown to be due to single vacancies. For Ta the results are less clear due to a considerable overlap of lines in the Moessbauer spectra. However, the spectra suggest vacancy mobility around or below room temperature. (author)

[en] Earlier Moessbauer effect experiments on ⁵⁷Co diffused in Al show two different positions for the Co-atoms after irradiation of the sample with fast neutrons: substitutional Co and interstitial Co. In order to study the landing dynamics of Co in Al we have implanted ⁵⁷Co in Al at 4.2⁰K, at which temperature the Al-interstitials are still immobile. The total implanted dose was 10¹⁴ at/cm², the implantation energy 85 keV. The Moessbauer spectrum shows one line corresponds to substantial Co-atoms, the other one comes from interstitial Co-atoms (in the <100> Co--Al mixed dumbbell position). The population of the substitutional site, found to be 0.46 +- 0.02, can give information on the interaction potentials between Co--Al and Al--Al when the results are interpreted on the basis of a replacement collision model modified by taking into account a spontaneous trapping volume for the lattice atom recoil, around substitutional Co

[en] Several hyperfine interaction and channeling-backscattering experiments were performed on heavy ions implanted by isotope separator in ferromagnetic materials. Different lattice sites may be possible for the implanted impurities. The relative populations of these sites may be different for each element and may vary with total implanted dose. One assumes there is a substitutional site and sites associated with one or more vacancies. These phenomena have obviously to be explained by means of the interaction of the implanted atoms with the radiation damage generated during implantation. The results were explained by means of a relatively simple model. First a mathematical model was set up. The different sites are fed with certain intensities. Transitions are possible between the different sites due to the presence of defects. Bearing this in mind one can write down a set of simultaneous differential equations with unspecified coefficients. Giving expressions for these coefficients, i.e. imposing a physical model, one can solve the differential equations. Doing so we were able to produce a curve which explains, at least qualitatively, the evolution of the substitutional fraction of the implanted atoms as a function of implanted dose

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[en] Rresented are the results of a mathematical model to calculate the concentrations of mono- and di-interstitials, mono- and divacancies and the interstitial and vacancy clusters and the fractions of Co impurity atoms associated with these defects as a function of the irradiation dose and during a thermal annealing treatment. The Co- defect fractions have been measured using Moessbauer spectroscopy and these experimental results have been used to check the model calculations and to adjust certain parameters. (author)

No abstract available