BS EN ISO 10704:2015 pdf download – Water quality — Measurement of gross alpha and gross beta activity in non-saline water — Thin source deposit method
4 Principle IMPORTANT — Gross alpha and gross beta determinations are not absolute determinations of the sample alpha and beta radioactive contents, but relative determinations referred to specific alpha and beta emitters that constitute the standard calibration sources. In order to obtain a thin deposit directly on a planchet, the sample can be progressively evaporated to dryness at a temperature below about 85 °C. Alternatively, for alpha determination, it can be concentrated via a coprecipitation, the filtered coprecipitate being measured on to the planchet (Reference [3]). The gross alpha and gross beta activity of the deposit is measured by counting in an alpha- and beta-particle detector or counting system previously calibrated against alpha- and beta-emitting standards. When suspended matter is present in a significant quantity, a filtration step is required and the gross alpha and gross beta activity can also be determined for the material retained on the filter. IMPORTANT — Due to the ingrowth of radon daughters over time, the results are dependent on the time elapsed between sample preparation and measurement. For comparison purposes, it is recommended that the measurement be performed at the same time after the preparation of the sample. 5 Chemical reagents and equipment
5.1 Reagents All reagents shall be of recognised analytical grade and shall not contain any detectable alpha and beta activity, except for radioactive standards solutions.
5.1.1 Standard solutions Alpha standard The choice of alpha standard depends on the knowledge of the type of radioactive contaminant likely to be present in the waters being tested. In general, this leads to a choice between naturally occurring and man-made alpha emitters. Commonly used standards of artificial alpha-emitting radionuclides employed for this purpose are 241 Am solutions and 239 Pu solutions. When 239 Pu is used, the presence of 241 Pu as an impurity shall be taken into account as it leads to growth of 241 Am in prepared standard solutions of sources. When 241 Am is used, take into account the potential interferences of its gamma emission. NOTE An uranium compound of certified natural or known isotopic composition has one arguable advantage, in that its specific activity can be calculated from established physical constants and isotopic abundance date which are independent of the calibration procedures of a particular organisation. However, an uranium compound of known isotopic composition is difficult to obtain. Furthermore, since the energies of the alpha emissions from uranium isotopes are less than those from the artificial transuranic nuclides, the use of a uranium standard tends to give a high result for transuranic elements. Beta standard The choice of beta standard depends on knowledge of the type of radioactive contaminant likely to be present in the waters being tested. As a natural material, 40 K as potassium chloride, dried to constant mass at 105 °C, can be used. Standard solutions of artificial beta-emitting radionuclides 90 Sr 90 Y are commonly used.
5.1.2 Wetting or surfactant agents Vinyl acetate
5.1.3 Volatile organic solvents Ethyl alcohol
5.1.4 Water, complying with the requirements of ISO 3696, grade 3.
5.1.5 Specific reagents for alpha-emitting radionuclides co-precipitation Ammonium hydroxide solution, c(NH 4 OH) = 6 mol/l. Nitric acid, concentrated, c(HNO 3 ) = 15,8 mol/l. Sulfuric acid solution, c(H 2 SO 4 ) = 1 mol/l. Iron carrier, solution of 5 mg of iron per millilitre. Barium carrier, solution of 5 mg of barium per millilitre.
5.2 Equipment
5.2.1 Laboratory equipment for direct evaporation
Usual laboratory apparatus to store and prepare the sample as specified in ISO 5667-3.
A hot plate, an automatic evaporator or any other appropriate apparatus.
5.2.2 Special equipment for alpha-emitting radionuclide co-precipitation Hot plate with stirring equipment Infrared lamp Vacuum filtration system Filters, of pore size 0,45 µm.
5.2.3 Planchet (counting trays)
The planchet shall be lipped and of stainless steel. The diameter of the planchet is determined taking account of the detector diameter and source holder dimensions of the counter used. In the specific case of co-precipitation, an annular support is used to fix the filter on to a filter holder or on to the planchet.