Six direct methods for standardisation of 152Eu

In the course of the past 40 years, IRMM has developed a large number of direct methods for the accurate standardisation of radionuclide solutions, all providing traceability to the SI unit. Six different measurement methods were employed to standardise a 152Eu solution in the frame of a BIPM key comparison: C)-γ-coincidence counting, using a modified version of the ‘Funck’ pressurised proportional counter (Ar–CH4) for counting the electrons and low-energy photons, and a 15×15 cm NaI(Tl) well crystal for counting the γ-rays; C)-γ-sum counting using the same equipment as above; coincidence counting, using a 2D shaped proportional counter (Kr–CH4) sandwiched between two 7.5×7.5 cm2 NaI(Tl) crystals; unting, using a 15×15 cm2 NaI(Tl) well crystal; Tl) counting; scintillation counting (LSC) using the CIEMAT/NIST method. ethods will be described and compared, with emphasis on their strengths and weaknesses. In the case of 152Eu, we were able to achieve a standard deviation of the weighted mean of 0.14% among all methods, or 0.11% when excluding the LSC result.