ISO 9698:2019

ISO 9698:2019 pdf free.Water quality – Tritium – Test method using liquid scintillation counting.
4 Principle
The test portion is mixed with the scintillation cocktail in a counting vial to obtain a homogeneous medium. Electrons (Beta particles) emitted by tritium transfer their energy to the scintillation medium. Molecules excited by this process return to their ground state by emitting photons that are detected by photodetectorsifil.
The choice of the analytical procedure (either with or without distillation of the water sample prior to determination), depends on the aim of the measurement and the sample characteristics[19112-Q1121].
Direct measurement of a raw water sample using liquid scintillation counting[i shall consider the potential presence of other beta emitter radionuclides. To avoid interference with these radionuclides when they are detected, the quantification of tritium is performed following the sample treatment by distilJationl2.Z1[2.JLZ4]LZ]. Annexes B. I and .E describe three distillation procedures.
In order to determine the background count rate, a blank sample is prepared in the same way as the test portion. 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 efficiency, it is necessary to measure a water sample having a known tritium activity under conditions that are identical to those used for the test sample. This water shall be a dilution of this mixture produced with the reference water, or a water with a traceable tritium activity usable without dilution.
The conditions to be met for the blank sample, the test portion and the calibration source are:
— same scintillation cocktail;
— same type of counting vial;
— same filling geometry;
— same ratio between test portion and scintillation cocktail;
— temperature stability of the detection equipment;
— value of quench indicating parameter included in calibration curve.
If particular conditions of chemical quenching affect the measurement results, it is recommended to correct the counting data using a quench curve (see 7.3.2).
5 Reagents and equipment
Use only reagents of recognized analytical grade.
5.1 Reagents
5.1.1 Water for the blank
The water used for the blank shall be as free as possible of chemical impurities to avoid quenching, of radioactive impuritiesL21IZZ] and with an activity concentration of tritium negligible in comparison with the activities to be measured.
For example, a water sample with a low tritium activity concentration can be obtained from (deep) subterranean water kept in a well-sealed borosilicate glass bottle in the dark at controlled temperature (see Iso 5667-3). This blank water sample shall be kept physically remote from any tritium containing material.
It is advisable to keep an adequate quantity of blank water in stock and to make small working amounts from it for immediate use as required. Contamination with tritium (e.g. from water vapour in the air and from tritium sources such as luminous watches and gas chromatographs) or other radioactive species should be avoided.
Determine the tritium activity concentration, in Bq[1, of this water and note the date of the determination.
As the activity is becoming non-negligible for activities around 1 Bq•frl, it is necessary to use a blank water measured to ensure the “absence’ oftritium. The tritium activity concentration in the blank water can be determined by enrichment followed by liquid scintillation counting or from the measurement of 3He by mass spectrometry. Preferably use blank water with a tritium activity concentration of less than 0,5 Bq.l-1.ISO 9698 pdf download.

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