Application of 57Fe emission Mössbauer spectroscopy to the investigation of the physico-chemical consequences of the double radioactive decay 57Ni→57Co→57Fe in the solid state

Abstract

⁵⁷ Fe emission Mössbauer spectroscopy is shown to be a useful technique for investigating the cumulative recoil and Auger after-effects associated with the double electron capture decay, ⁵⁷Ni→⁵⁷Co→⁵⁷Fe, 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 ⁵⁷Ni-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 ⁵⁷Fe or ⁵⁷Co. In line with the energetics of the ⁵⁷Ni radioactive filiation, recoil of nucleogenic ⁵⁷Co atoms is systematically observed in ⁵⁷Ni-labelled samples when the decay into ⁵⁷Co and the subsequent Mössbauer analysis were achieved at low temperatures (<90 K). A pronounced matrix influence related to the stabilization of nucleogenic Feⁿ⁺ species in a nickel-based host lattice is described. The complexity of the emission Mössbauer spectra obtained in nickel(II) carboxylates is shown to reveal cumulative recoil, electronic and self-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.