Applications and Conclusions

Abstract

The information which can be obtained from isotope shifts is very different in different elements. In the simplest element, hydrogen, the interest is more in the shift from the hypothetical infinitely heavy point nucleus than in the shift between actual isotopes. This is because there is no doubt about the structure of a single-electron atom but a comparison of experiment with theory enables the theory involved, relativistic quantum electrodynamics, to be tested. One quantity which at present has to be inserted as an experimental fact of life, without any generally accepted evaluation of its value from theory, is the electron-to-proton mass ratio. As mentioned in Section 3.1, the best value for this ratio may come from isotope shift measurements in the spectrum of hydrogen, but an alternative method (Gräff et al., 1980), which may give even higher precision, is to compare the cyclotron frequencies of protons and electrons in the same magnetic field. Another quantity which has to be measured is the size of the nuclear charge distribution, but in the case of hydrogen the field shift is barely significant, even in the most precise work, and so only an approximate value is required.