Very Fast and Field Measurement of Ra-226 by Liquid Scintillation Spectrometry

Franz Schönhofer

Federal Ministry for Agriculture, Forestry, Environment and Water Management, Department of Radiation Protection, Vienna, Austria

Karl Irlweck

Institute of Inorganic Chemistry, Radiochemistry, University of Vienna, Austria

Karl Buchtela

Atominstitute of the Austrian Universities, Vienna, Austria

About fifteen years ago new separation methods have been introduced also commercially, which make use of element-specific extraction by crown-ethers and other suitable extractants. These extractants may be dissolved and act via liquid-liquid extraction, but they may as well be fixed on an inert support and act via reverse chromatography. Some years ago, filters were introduced, impregnated with selective extractants. An old dream from early work with separation and isolation of various radionuclides seems to become true: You pour a solution you want to analyse for certain radionuclides through the specific filter, you wash the filter, you put it into a liquid scintillation vial, add a suitable liquid scintillation cocktail and after counting it, you have a specific results for a specific radionuclide.

One candidate for such an easy determination is Ra-226.

Using an adapted method for extraction of Rn-222 from the Ra-226 containing water in the former laboratory of FS, with the ultra low-level liquid scintillation spectrometers “Quantulus” (Wallac OY, Turku, Finland) an LLD of less than 30 mBq/l could be achieved, using 10ml of untreated water. A drawback was that establishment of equilibrium between Ra-226 and Rn-222 took quite a long time.

In order to overcome the drawback of this long waiting time, we have tested the “3M Empore Radium Rad Disks”, which are able to extract under carefully controlled conditions radium selectively.

This paper describes the experiments, considerations as to the presence of other radiumisotopes (Ra-228 and Ra-224), and the use of alpha-beta separation to distinguish between the different radium isotopes. Considerations as to the simultaneous determination of these radium isotopes will be described, as well as the LLD’s to be achieved with this method. .

We have tested as well the possibility of performing these analyses in the field by using a commercially available portable liquid scintillation spectrometer equipped with alpha-beta discrimination (“Triathler” of Hidex OY, Turku, Finland). The results under field conditions will be presented.