Abstract. Internal conversion coefficients involving atomic electrons (ICC) and electron-positron pairs (IPC) are often required to determine transition multipolarities and total transition rates. A new internal conversion coefficient data base, BrIcc has been developed which integrates a number of tabulations on ICC and IPC, as well as Ω(E0) electronic factors. To decide which theoretical internal conversion coefficient table to use the accurately determined experimental α K , α L , α Total and α K /α L values were compared with the new Dirac-Fock calculations using extreme assumptions on the effect of the atomic vacancy. While the overall difference between experiment and theory is less than 1%, our analysis shows preference towards the so called Frozen Orbital approximation, which takes into account the effect of the atomic vacancy.