BS ISO 13168:2015 pdf download

BS ISO 13168:2015 pdf download.Water quality — Simultaneous determination of tritium and carbon 14 activities — Test method using liquid scintillation counting
1 Scope
This International Standard describes a test method for the simultaneous measurement of tritium and carbon-14 in water samples by liquid scintillation counting of a source obtained by mixing the water sample with a hydrophilic scintillation cocktail. This is considered a screening method because of the potential presence of interfering nuclides in the test sample. The method can be used for any type of environmental study or monitoring. This International Standard is applicable to all types of waters having an activity concentration ranging from 5 Bq/l to 10 6 Bq/l (upper limit of the liquid scintillation counters for direct counting). For higher activity concentrations, the sample can be diluted to obtain a test sample within this range.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and sampling techniques
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 9698, Water quality — Determination of tritium activity concentration — Liquid scintillation counting method
ISO 80000-10, Quantities and units — Part 10: Atomic and nuclear physics
ISO 11929, Determination of the characteristic limits (decision threshold, detection limit and limits of the confidence interval) for measurements of ionizing radiation — Fundamentals and application
ISO/IEC Guide 98-3:2008, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in measurement (GUM:1995)
ISO/IEC Guide 99:2007, International vocabulary of metrology — Basic and general concepts and associated terms (VIM)
4 Principle
The test sample is mixed with the scintillation cocktail in a counting vial to obtain a homogeneous medium. Electrons emitted by the radionuclide transfer their energy to the scintillation medium. Molecules excited by this process return to their ground state by emitting photons that are detected by photodetectors. The electric pulses emitted by the photodetectors are amplified, sorted (in order to remove random events) and analysed by the electronic systems and the data analysis software. The count rate of these photons allows the determination of the test sample activity, after correcting for the background count rate and detection efficiency. In order to determine the background count rate, a blank sample is prepared in the same way as the test sample. The blank sample is prepared using a reference water of the lowest activity available, also sometimes called “dead water”. In order to determine the detection efficiencies, it is necessary to measure a water sample having known tritium and carbon 14 activities under conditions that are identical to those used for the test sample. This water shall be a mixture of certified radioactive sources or a dilution of this mixture produced with the reference water.