Determination of 228Ra, 226Ra and 224Ra in natural water via adsorption on MnO2-coated discs.

A fast procedure based on sorption of Ra on MnO2 coated polyamide discs is presented for determination of radium isotopes (i.e. 228Ra, 226Ra, 224Ra) in aqueous samples. The sample discs can be used directly for low-level alpha-spectrometry without the need for further separation and preparation methods to produce planar sample sources. While the activity of alpha-emitting 224Ra and 226Ra can be determined during a first measurement, beta-emitting 228Ra is obtained via ingrowth of the progeny 228Th on the same sample disc after a standing time of about six months. Calculations are presented for optimizing the analytical accuracy as well as for predicting the sorption yield or chemical recovery of radium on the sample disc as a function of exposure time because the sorption uptake proceeds with first-order kinetics. The analyses can be carried out on small samples of 0.5-11 and, for long counting times of one week and use of high-purity silicon surface barrier detectors, a detection limit of 0.15 mBq l-1 is obtained for 226Ra. Since the half-life of 224Ra is only 3.7 d and since 228Th (as a measure for 228Ra) is built up only partially on the sample disc, a slightly higher detection limit of 0.24 mBq l-1 results for the latter isotopes. The procedure is therefore sufficiently sensitive to allow the investigation of Ra isotope relationships in aquifers at typical environmental levels.

Soil gas measurements below foundation depth improve indoor radon prediction.

A soil gas measurement method developed earlier, [Nucl Tracks Radiat Meas, 22(1-4) (1993) 468] was applied to boreholes drilled to below foundation depth. Radon concentration and permeability were measured at 50-cm intervals. In radon prone areas, permeability showed an increase with depth over several orders of magnitude, indicating a low permeability top layer with a thickness of 0.5 m and more. A radon availability index (RAI) was empirically defined and the maximum RAI of each boring proved to be a reliable indicator for radon problems in nearby houses. The permeability of the top layer also proved to be an important factor for a better understanding of soil gas transport and the influence of rain. Implications for radon mitigation are derived.

Alpha spectrometry sample preparation using selectively adsorbing thin films

Several years ago, Switzerland introduced limits for natural radionuclides in food, e.g. 1 Bq/l for 226Ra or 10 Bq/l for the sum of 238U and 234U in drinking water. To make enforcement by regional (cantonal) laboratories more attractive, simplified analytical methods had to be offered, at least for drinking water. A first step has been the development of radium adsorbing sheets. A 20 mm x 20 mm MnO2 film on a polyamide substrate adsorbs more than 80% of the radium present in a 100 ml water sample within 6 h. The film is thin enough to allow for high resolution alpha spectrometry. A second step now under way is to produce thin films, which selectively adsorb uranium. Actually, an ion exchange resin with diphosphonic and sulfonic acid groups is used for this purpose. Although not yet very thin, these films make possible energy resolutions far better than with any liquid scintillation alpha spectrometry method. Adsorption efficiencies are more than 80% after 20 h exposition to a 100 ml water sample (20 mm x 20 mm sheet). A third step is to have a system that measures radionuclide concentrations in water on-line. A prototype is presented where radionuclides are adsorbed on a film in contact with the water. A Si-detector placed on the other side of the film support counts the alphas passing through.

Determination of natural radionuclides in drinking water; a tentative protocol.

Routine analysis of drinking water is in general limited to artificial radionuclides although some naturally occurring radionuclides have radiotoxicities well comparable to those of the worst artificial ones. This unsatisfactory situation is mainly due to problems with traditional radiochemical preparation methods. They are very time consuming and the chemistry involved is too high a hurdle for many laboratories. A simplified protocol for the determination of natural radionuclides in drinking water has been setup and tested. It makes full use of the gamma-spectrometry's analyzing power and of state-of-the-art liquid scintillation alpha-spectrometry combined with extractive scintillators. It also includes the use of metal-adsorbing thin layers for direct alpha-spectrometry. The protocol does not offer record-low detection limits, but allows for a rapid check that no individual natural radionuclide present in the water will contribute more than 50 microS v to the annual dose.