Tensorial form and matrix elements of the relativistic nuclear recoil   operator
  Within the lowest-order relativistic approximation ($\sim v^2/c^2$) and to first order in $m_e/M$, the tensorial form of the relativistic corrections of the nuclear recoil Hamiltonian is derived, opening interesting perspectives for calculating isotope shifts in the multiconfiguration Dirac-Hartree-Fock framework. Their calculation is illustrated for selected Li-, B- and C-like ions. The present work underlines the fact that the relativistic corrections to the nuclear recoil are definitively necessary for getting reliable isotope shift values. 
E. Gaidamauskas, C. Naz\'e, P. Rynkun, G. Gaigalas, P. J\"onsson and   M. Godefroid
physics.atom-ph