Intercomparison of measurement of tritiated water by internal proportional gas counting

An international intercomparison of measurements of tritiated water by means of internal proportional gas counting has been carried out under the auspices of EUROMET, a European collaboration in measurement standards. The measurements were made at the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (Germany), the National Institute for Standards and Technology (NIST), Gaithersburg (USA) and the National Physical Laboratory (NPL), Teddington (UK). The current work follows an intercomparison reported at ICRMʹ93 [J.L. Makepeace et al., Nucl. Instr. and Meth. A 339 (1994) 343], between NPL, PTB, NIST and the Laboratoire Primaire de Métrologie des Rayonnements Ionisants (LPRI), Saclay (France), of measurements of tritium gas contained in a cylinder, in which agreement within the stated uncertainties had been achieved. s of the same tritiated water were distributed to the participating laboratories for measurement. The methods used to reduce the water to tritium gas and its subsequent measurement by internal proportional gas counting are described, together with the results obtained and the experimental uncertainties associated with the measurements.