High resolution gamma-ray spectroscopy: the first 85 years

This opening review attempts to follow the main trends in crystal diffracti on spectrometry of nuclear gamma rays from its 1914 beginning in Rutherford 's laboratory to the ultra-high resolution instrumentation realized in the current generation of spectrometers at the Institute Laue Langeven (ILL). M y perspective is that of an instrumentalist hoping to convey a sense of our intellectual debt to a number of predecessors, each of whom realized a cer tain elegance in making the tools that have enabled much good science, incl uding that to which the remainder of this workshop is dedicated. This overv iew follows some of the main ideas along a trajectory toward higher resolut ion at higher energies, thereby enabling not only the disentangling of dens e spectra, but also allowing detailed study of aspects of spectral profiles sensitive to excited state lifetimes and interatomic potentials. The paral lel evolution toward increasing efficiency while preserving needed resoluti on is also an interesting story of artful compromise that should not be neg lected. Finally, it is the robustness of the measurement chain connecting g amma-ray wavelengths with optical wavelengths associated with the Rydberg c onstant that only recently has allowed gamma-ray data to contribute to dete rmination of particle masses and fundamental constants, as will be describe d in more detail in other papers from this workshop.