Standardisation of 125I using seven techniques for radioactivity measurement

Seven methods of radioactivity measurement were used to standardise an 125I solution within the frame of an international key comparison organised by BIPM: photon-photon coincidence counting with two NaI detectors, photon sum-peak counting in a NaI well detector and in a 4π CsI(Tl) sandwich spectrometer, total emission counting in a windowless 4π CsI(Tl) sandwich spectrometer, electron-X,γ coincidence counting and electron-X,γ sum counting in a pressurised proportional counter inside a NaI well detector and liquid scintillation counting with the CIEMAT/NIST method. The solid sources were prepared by quantitative drop deposition with addition of AgNO3. The measurement methods, the results and the applied corrections are described and discussed.