The inelastic channel in time-domain Moessbauer spectroscopy

Time-domain Moessbauer 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