Time Dependence of Recoil-Free Resonance following Electron Capture inCo57

Abstract

The use of delayed-coincidence techniques in conjunction with the Mössbauer effect permits measurements of the time evolution of the Mössbauer resonance following formation of the resonant nuclear level. A series of measurements are reported in which the time dependence of ${\mathrm{Fe}}^{57}$ chemical charge states was studied for sources of ${\mathrm{Co}}^{57}$ (which decays to ${\mathrm{Fe}}^{57}$) embedded in various compounds: CoO, NiO, Fe${\left(\mathrm{N}{\mathrm{H}}_4\right)}_{2-}$ ${\left(\mathrm{S}{\mathrm{O}}_4\right)}_2$·6${\mathrm{H}}_2$O, CoS${\mathrm{O}}_4$·7${\mathrm{H}}_2$O, and Co${\mathrm{Cl}}_2$·4${\mathrm{H}}_2$O. These are systems in which the resonance spectra had previously been interpreted in terms of metastable chemical charge states possessing lifetimes comparable to the nuclear life time (100 nsec). In no case were time effects observed which could not be attributed to "time filtering" of the emitted radiation by the resonant absorber. The appearance of multiple emission lines is interpreted in terms of equilibrium between ferric and ferrous ions, the relative intensities probably being determined by the amount of deviation of the samples from stoichiometry.