The inelastic channel in time-domain Mössbauerspectroscopy

Abstract

Time-domain Mössbauer spectroscopy has been interpreted by Hamermesh using a classical optical model. One of the most interesting aspects of the experiments is the observation of a “speed-up” effect. This speed-up effect can be observed by measuring the gamma radiation coming from the source after transmission through a nuclear-resonant “filter”, i.e., the elastic channel, using the delayed-coincidence time-to-amplitude conversion method. This time-domain speed-up effect occurs in the coherent forward scattering of the nuclear-resonant gamma radiation. Time-domain nuclear-resonant forward scattering results observing the inelastic channel, i.e., the X-ray following internal conversion, using a radioactive source have not been obtained previously. Such results are presented for the radioactive-source case using both ⁵⁷Fe and ⁷³Ge. These two isotopes were chosen because of the differences in the values of the internal conversion coefficients α, i.e., α is 8 and 1310, respectively, for the two cases. In each case experimental data, using both the elastic channel and the inelastic channel, are given. Commercial sources and absorbers of iron-in-rhodium foils were used for the ⁵⁷Fe experiments. For the ⁷³Ge experiments, we prepared our own sources by electroplating ⁷³As onto Ge single crystals. The Ge absorber was the enriched ⁷³Ge single crystal originally prepared by Pfeiffer. Fits to the experimental elastic-channel data are given using the classical optical model. Our preliminary experimental results using the inelastic channel are inconclusive.