This volume deals with the interaction between moments of excited or radioactive nuclei and electromagnetic fields. The experimental techniques developed for the observation of this hyperfine interaction are governed by the lifetime of the nuc­ lear states in question. The dynamics of the interaction are reflected by the time dependence of the spatial distribution of the radioactive decay radiation. Basically, the experiments yield information on the energy shifts and/or splittings of the nuc­ lear levels. These quantities are determined essentially by the product of the nuc­ lear moment and the electromagnetic field acting at the site of the nucleus. Due to the strong decrease in the fields with distance, the measurements probe these fields within a highly localized region centered around the radioactive nuclei. Detailed experimental methods with numerous ramifications were developed in the early sixties. In the period which followed, the main emphasis was on excitation of short-lived nuclear states by means of pulsed particle accelerators, implantation of radioactive nuclei, and production of polarized a-unstable nuclei by nuclear re­ actions with polarized neutrons or particles. The seventies were a period of fruit­ ful applications directed to extensive studies of the moments of excited nuclear states on the one hand, and local internal fields on the other, resulting in far­ reaching information on atomic and solid-state properties. The organization of this Topics volume follows these main lines of research.

1. Introduction.- 1.1 Perturbed Angular Distribution Techniques.- 1.2 Perturbed Angular Correlation Techniques.- 1.3 Nuclear Magnetic Resonance on ?-Emitting Nuclei.- References.- 2. Hyperfine Interactions of Excited Nuclei in Atomic Systems.- 2.1 Free Atoms in Flight-The Recoil Distance Method.- 2.2 Atoms in Gases.- 2.3 Magnetic Decoupling Measurements in Vacuum.- 2.3.1 Fields Parallel to the Quantization (Beam) Axis.- 2.4 New Methods and Future Directions.- References.- 3. Hyperfine Interaction Studies in Nuclear Physics.- 3.1 Overview.- 3.2 Hyperfine Hamiltonian and Nuclear Moments.- 3.3 Laser Spectroscopy and Hyperfine Structure of Exotic Nuclear States.- 3.4 Nuclear Moments of High-Spin States.- 3.5 Magnetic Moments of Simple Shell-Model Configurations.- 3.6 Hyperfine Interactions in Nuclear ? Decay.- References.- 4. Hyperfine Interactions of Defects in Metals.- 4.1 Relevant Solid State and Nuclear Physics Aspects.- 4.2 Hyperfine Investigations of Defects.- References.- 5. Electric Quadrupole Interaction in Noncubic Metals.- 5.1 Electric Quadrupole Hyperfine Interaction.- 5.2 Experimental Methods.- a) Nuclear Resonance Methods.- b) Perturbed Angular Correlation (Distribution) Methods.- 5.3 Experimental Data and Systematic Trends.- 5.4 The EFG in Metals.- 5.4.6 Pressure and Concentration Dependence.- 5.5 Conclusion.- 5.6 Appendix.- Table of Experimental Data on Quadrupole Interaction in Noncubic Metals.- References.- 6. ? Emitters and Isomeric Nuclei as Probes in Condensed Matter.- 6.1 Theory.- 6.2 Experimental Methods.- 6.3 Metals.- 6.4 Insulators.- 6.5 Tabular Summary.- References.