Hyperfine structure early measurements

The phenomenon of hyperfine structure has been well-known since the early days of spectroscopic experiments. At the very beginning hyperfine effects were attributed to the occurrence of different isotopes in the substances measured. This explanation soon had to be replaced due to the fact that the measured line spacings substantially exceeded... 

Hyperfine structure due to nuclei of the crystal matrix can be resolved to provide information about the trapping site as demonstrated already in early ENDOR studies of solids [1]. The distances from the paramagnetic centre to nuclei of the matrix can be measured. 

Spectroscopy on the hydrogen molecular ion is difficult. Early results came from photoelectron (14), photoionization (15) and Rydberg spectra (16). Dehmelt and Jefferts (17) succeeded in measuring the radiofrequency spectra of H+ and characterizing the hyperfine structure in the vibrational levels v=4-8. 

The motivation for hyperfine structure and isotope shift studies in the isoelectronic case of Ra II and in Ra I came originally from nuclear physics. After early measurements of the atomic energy levels on the long-lived Ra/ the isotope shifts and the hyperfine structures of the odd-A isotopes remained inaccessible until recentlyThe extraction of nuclear moments required the analysis of the electronic hyperfine fields which was performed in on-line collinear-beam studies of several transitions involving the 7s Si/2 and Ip Pi/2 states of Ra II and all states of the 7s7p configur-... 

The first of the macroscopic quantum effects to be demonstrated was the ac Josephson effect, whereby 2e/h is established via the invariant ratio nV/V for irradiation at frequency V and noting the n th step voltage, V. This has been a powerful tool in the service of electrical measurements. The history, which has been well reviewed by Petley, shows a rapid evolution from laboratory curiosity through a significant determination of a to the role of maintenance of the operational unit of voltage [16]. Incidentally, the early history of this area of work is an instance in which electrical metrology made a distinct impact on atomic physics. It will be recalled that a key issue of the early 1960 s was the discrepancy between values of a obtained from fine-structure measurement and those deduced from hyperfine structure. This story is well told in the widely known summary, due to Taylor,... 

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