The time dependence of ${\mathrm{Fe}}^{57}$ chemical charge states in sources of ${\mathrm{Cu}}_2$O, MgO, and ${\mathrm{Al}}_2$${\mathrm{O}}_3$ doped with ${\mathrm{Co}}^{57}$ has been studied by means of the Mössbauer effect. Charge states of ${\mathrm{Fe}}^{1+}$, ${\mathrm{Fe}}^{2+}$, ${\mathrm{Fe}}^{3+}$, and ${\mathrm{Fe}}^{4+}$ resulting from the $K$-capture decay of the ${\mathrm{Co}}^{57}$ have been detected. Delayed-coincidence measurements showed no time dependence of the relative peak intensities of these charge states. A time-dependent narrowing of the resonance lines is observed which is not ascribable to "time filtering" alone. The isomer shifts of the different valence states are discussed in terms of $3d$-electron shielding.

• Received 13 March 1969

DOI:https://doi.org/10.1103/PhysRev.187.491