The new international reference system for pure alpha- and pure beta-emitting radionuclides and some electron capture decaying radionuclides by liquid scintillation counting
Abstract
The Bureau International des Poids et Mesures (BIPM) is developing with the support of national metrology institutes an extension to the existing international reference system of radionuclide metrology to address pure alpha-, pure beta-emitting and some electron capture-decaying radionuclides. The new service is based on a liquid scintillation counter and the triple to double coincidence (TDCR) technique. A dedicated facility to prepare liquid scintillation sources and a TDCR system have been set up at the BIPM. The TDCR system was conceived and commissioned in order to ensure the long-term reproducibility of the reference it produces. The metrology is based on a dedicated approach which uses the TDCR value as a parameter to stabilize the output quantities of the system against changes in detection efficiency or asymmetry that could appear in a long-term period of operation. The quality assurance based on periodic controls of toluene-based liquid scintillation sources of H-3 and C-14 has permitted to demonstrate the reproducibility of the system for a 20-month period.