An extension of the international reference system (ESIR) for radionuclide metrology has been developed and put into operation at the BIPM following three years of joint effort. The ESIR allows measurement of radionuclides that could not be measured by the existing system and thus makes it possible for degrees of equivalence to be obtained for these specific isotopes by NMIs/DIs. An article has been published in the Journal of Radioanalytical and Nuclear Chemistry, which describes in detail the liquid scintillation counting system and the liquid scintillation source preparation facility that have been developed for this new BIPM measurement service. Its development has been supported by the crucial scientific expertise of our partners LNE-LNHB (France), PTB (Germany), POLATOM (Poland), and NIM (China) who are at the forefront of this technique.