BS EN ISO 10704:2019 pdf free download – Water quality – Gross alpha and gross beta activity – Test method using thin source deposit.
Keep planchets that are not to be used immediately in a dessicator to prevent any modification by ambient atmosphere in the laboratory.
Weigh the planchets before use, and record the mass, mp. If a co-precipitation method is used, weigh the filter (5.2.2.1) with the planchet before use, and record the mass, mpf.
Avoid reuse of planchets to minimize cross-contamination. If the planchets are reused, their freedom from contamination shall be demonstrated.
7.2.2 Evaporation
Transfer the test portion on to the planchet using automatic or non-automatic equipment with a known uncertainty (pipette, water distribution system) and carefully evaporate to dryness.
The residue deposited should form a thin layer of uniform surface density to limit self-absorption phenomena and to ensure similarity with the calibration source geometry.
After cooling the planchets to ambient temperature, weigh them and record the mass, mpd. The mass deposited, m, is given by Formula (1):
If hygroscopic salt deposit is expected the planchet can also be weight at the end of the measurement.
To minimize any loss by spitting, maintain the temperature below about 85 °C over the entire planchet surface to avoid any overheated areas.
Before evaporating the test portion to dryness on the planchet, pre-evaporation can be performed with appropriate equipment (5.2.1).
A homogeneous deposit is best achieved on etched or sandblasted planchets. If the deposit is not homogeneously spread, add a wetting agent or surfactant (5.1.3).
7.2.3 Co-precipitation
The recommended working volume is 500 ml.
If a test portion of lower volume is to be analysed, make up to 500 ml with water.
If a test portion of higher volume is to be analysed, concentrate it by evaporation (5.2.1) to 500 ml.
Adjust the pH of the working volume to 7,0 ± 0,5.
Add 20 ml of sulfuric acid (5.1.6.3) and boil for 5 mm on a hot plate while stirring.
At a temperature of approximately 50 °C, add 1 ml of the barium carrier solution (5.1.6.5) and stir for 30 mm.
The barium sulfate precipitates.
Then add 1 ml of the iron carrier solution (5.1.6.4).
Adjust the pH with ammonium hydroxide, (5.1.6.1) drop by drop until iron(III) hydroxide precipitates.
Continue stirring for 30 mm.
Filter (5.2.3.4) the co-precipitates.
Place the filter on to the identified planchet and fix it by an annular support to avoid deformation while drying.
Dry at moderate temperature.
7.3 Counting stage
Following evaporation (7,2.2) or co-precipitation (7.2,3), if the counting is not performed immediately the planchet with the deposit can be stored in a desiccator.
The measurement of the residue activity on the planchet is performed by counting for an appropriate duration to reach the required characteristic limits and depending on the test portion and background count rates.
The counting strategy depends on the objectives of the measurements and the regulator requirements. To monitor natural radionuclides ingrowth or decay (see 9Z[1), counting procedures should be repeated periodically over a period of one month. If specific counting condition is applied, it is recommended to mention it in the report.
When the counting strategy is defined, the laboratory shall apply it systematically for comparison purposes.
7.4 Background and blank determination
Measure the background activity using a clean planchet (5.2.2.2) under conditions representative of the measurement method. Repeated counts confirm the stability of the background level.
If reagents are used, measure the blank activity using a clean planchet and reagents under conditions representative of the measurement method. Repeated counts confirm the stability of the blank level.