The massic activity of a solution containing 188W in equilibrium with its daughter, 188Re, has been standardized by the National Institute of Standards and Technology using 4pi beta liquid scintillation counting with efficiency tracing using the CIEMAT NIST method. Confirmatory measurements were carried out with gamma-ray spectrometry using high purity germanium detectors and a 4pi gamma NaI(Tl) system. A calibration factor of 1.68 MBq pA(-1) +/-0.03 MBq pA(-1) (expanded, k = 2, uncertainty) for the 188W in the solution was determined, along with correction factors for activity determinations using Capintec dose calibrators. A half-life value of 69.78 d +/- 0.05 d (standard uncertainty) was determined by measurement in the NIST 4pi gamma ionization chamber and is consistent with currently recommended values.
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