1 Total α Radioactivity
1.1 Low background total α detection method
1.1.1 Scope
This standard specifies three determination methods for the volume activity of the total α radioactivity of α radionuclide in drinking water and its source water.
This method is applicable to the determination of the volume activity of total α radioactivity of α radionuclide in drinking water and its source water.
If 226Ra is contained in drinking water, α radioactive daughter 222Rn generated during the period from burning of solid residue to completion of sample source measurement has interference on the determination result. The interference may be reduced by shortening the placing time of solid residue after burning and the finished sample source; it may be eliminated by regularly measuring the increase of α radioactive activity of solid residue along with the increase of placing time.
After being extended, this method may also be used for determining the volume activity of total α radioactivity of saline water and mineralized water, while the sensitivity is slightly decreased.
The detection limit of this method is depended on multiple factors such as the inorganic salt quantity contained in the water sample, the counting efficiency of counting measuring system, the background counting rate, the counting time, etc. Under typical condition, the detection limit of this method is 1.6×10-2Bq/L.
1.1.2 Principle
Acidize the water sample and transform it to sulfate through evaporation concentration, then burn it at 350℃. Transfer the residue to sample disk and make it into sample source, then measure α counting at α channel of low background α and β measuring system.
For drinking water, three methods may be selected for detecting the volume activity of total α radioactivity: the first method is thick sample method which determines the instrument counting efficiency of measuring system with electroplating source and then determines the effective thickness through test; the second method is comparative measurement method which prepares and measures through the to-be-tested sample source and the standard source containing known quantity of reference material under the same condition; the third method is standard curve method which prepares the reference material powder into a series of standard sources with different mass thicknesses, measures the relationship between the counting efficiency of given standard source and the mass thickness of standard source, and draws α counting efficiency curve. The detection unit may select one method according to its own conditions.
1.1.3 Reagents
Foreword I
1 Total α Radioactivity
2 Total β Radioactivity
Appendix A (Normative) Reference Documents
