Absolute standardisation of a 58 Co solution using the 4 π β-γ coincidence method with germanium detector

The Laboratorio Nacional de Metrologia das Radiacoes Ionizantes (LNMRI), committed by INMETRO since 1989, has as main purposes, the maintenance of standards, metrological traceability and the establishment of measurement methods for ionizing radiation. To fulfil these objectives the LNMRI has participated, in 2000, in a comparison organized by Electrotechnical Laboratory - ETL (Japan) for the activity concentration determination of a 58 Co solution, using a recent implemented 4 π β-γ coincidence counting system, constituted by a pressurized proportional counter for β channel and a high purity germanium detector for γ channel. The evaluation of the activity concentration measurement was also made by the spectrometric method using the efficiency curve of germanium detector. To establish the confidence in the coincidence counting system, some 60 Co sources of known activity values, supplied by Bureau International des Poids et Mesures (BIPM) were measured and the results compared. Measurements of half-life of 58 Co were made with periodic lectures in a reference system based on a re-entrant γ-ionization chamber. The results of measurements of activity concentration of 5 samples show an overall uncertainty of 0.85%, with 68% of confidence level, appropriated for radionuclide metrology, and the value obtained for the half-live is consistent to those found in international references. (author)