Theory of the helium isotope shift

Abstract

Theory of the isotope shift of the centroid energies of light few-electron atoms is reviewed. Numerical results are presented for the isotope shift of the 23P-23S and 21S-23S transition energies of 3He and 4He. By comparing theoretical predictions for the isotope shift with the experimental results, the difference of the squares of the nuclear charge radii of 3He and 4He, δR2, is determined with high accuracy.