APPLICATION OF FE-57 EMISSION MOSSBAUER-SPECTROSCOPY TO THE INVESTIGATION OF THE PHYSICOCHEMICAL CONSEQUENCES OF THE DOUBLE RADIOACTIVE DECAY NI-57-]CO-57-]FE-57 IN THE SOLID-STATE

Fe-57 emission Mossbauer spectroscopy is shown to be a useful technique for investigating the cumulative recoil and Anger after-effects associated with the double electron capture decay, Ni-57-->Co-57-->Fe-57, in the solid state. Experimental results collected in several types of nickel-containing matrices are surveyed: conducting materials (Ni metal), ionic compounds with monoatomic ligands [potassium trifluoronickelate(II)] and coordination compounds with polyatomic ligands (carboxylates). The consequences produced at a molecular level by the two successive decays in Ni-57-labelled nickel compounds can be analysed provided that a strict methodological approach is followed, which compares with the results obtained on the same compounds doped with Fe-57 or (CO)-C-57. In line with the energetics of the Ni-57 radioactive filiation, recoil of nucleogenic Co-57 atoms is systematically observed in Ni-57-labelled samples when the decay into Co-57 and the subsequent Mossbauer analysis were achieved at low temperatures (<90 K). A pronounced matrix influence related to the stabilization of nucleogenic Fe-n+ species in a nickel-based host lattice is described. The complexity of the emission Mossbauer spectra obtained in nickel(II) carboxylates is shown to reveal cumulative recoil, electronic and seif-radiolytic effects. The influence of the ligands concerned is found to be in line with a 'double autoradiolysis model' taking into account the cumulative effects of the two radioactive decays.