Recoil-free Nuclear 19.5. Hyperfine Interactions

Conditions of Recoil-free Nuclear Hyperfine Interactions 573... 

Rudolph Mossbauer discovered the phenomenon of recoil-free nuclear resonance fluorescence in 1957-58 and the first indications of hyperfine interactions in a chemical compound were obtained by Kistner and Sunyar in 1960. From these beginnings the technique of Mbssbauer spectroscopy rapidly emerged and the astonishing versatility of this new technique soon led to its extensive application to a wide variety of chemical and solid-state problems. This book reviews the results obtained by MSssbauer spectroscopy during the past ten years in the belief that this will provide a firm basis for the continued development and application of the technique to new problems in the future. 

The Mossbauer effect involves the resonance fluorescence of nuclear gamma radiation and can be observed during recoilless emission and absorption of radiation in solids. It can be exploited as a spectroscopic method by observing chemically dependent hyperfine interactions. The recent determination of the nuclear radius term in the isomer shift equation for shows that the isomer shift becomes more positive with increasing s electron density at the nucleus. Detailed studies of the temperature dependence of the recoil-free fraction in and labeled Sn/ show that the characteristic Mossbauer temperatures Om, are different for the two atoms. These results are typical of the kind of chemical information which can be obtained from Mossbauer spectra. 

The total absorption intensity depends on the concentration of the Mossbauer atoms in the absorber and their recoil-free fraction. The recoil-free fraction depends on the binding forces of the Mossbauer atom in the lattice (see Ap.l). The number and position of the absorption lines are determined by electric and magnetic electronic effects, the hyperfine interactions, which shift and split the nuclear levels. The allowed transitions between ground and excited substates are determined by the multipolarity of the nuclear transition. The = transition of... 

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