Calculations of isotope shifts in caesium and thallium using many-body perturbation theory

Ab initio many-body perturbation calculations are presented for the field and the specific mass isotope shifts for caesium and thallium. The calculations are fully relativistic and incorporate the random phase approximation core screening corrections together with the lowest order correlation corrections. For the specific mass shift certain higher order corrections are also included. For the Cs 6s 1/2 ground state the authors obtain a field shift value which they believe is accurate to 3%. For Tl they find relatively poor agreement between the calculated field shift values at this level of approximation. Current experimental data are re-examined in the light of the results.