Standardization and decay data determinations of 125I, 54Mn and 203Hg

The absolute 4π–βγ coincidence counting has been used to measure the activity concentrations of 54Mn and 203Hg, and the Sum–Peak method was used for 125I. 54Mn and 125I radionuclides have been part of international key-comparisons coordinated by the Bureau International des Poids et Measures (BIPM) in 2003/2004, while 203Hg is part of the traceability programme of the National Laboratory for Ionizing Radiation Metrology (LNMRI)/Brazil. Three different detectors were used for the Sum–Peak method: 3″×3″ NaI(Tl) and 5″×5″ well NaI(Tl) scintillation detectors and a planar germanium detector. Direct measurements were made of the photon emission probabilities of the 35.5-, 834.8- and 279.2-keV γ-rays of 125I, 54Mn and 203Hg to give values of (0.0667±0.0014), (0.9997±0.0055) and (0.8161±0.0005), respectively. The half-lives of 203Hg and 54Mn were also determined by means of a 4πγ ionization chamber (203Hg) and by the reference source method using a HPGe detector (54Mn) to give values of (46.639±0.023) days and (312.1±0.9) days, respectively.