226Ra, 222Rn AND PERMEABILITY OF BELGIAN SOILS IN RELATION WITH INDOOR RADON RISK.

Knowing the concentration of 226Ra in soil and of 222Rn in soil gas is important for the analysis of indoor radon data and the prediction of radon-prone areas. Except for soil Rn in Ardenne, the data concerning these two radionuclides in Belgian soils are very scarce. In the context of Master theses and international courses, students made 92 measurements of 226Ra in soil samples, 105 of 222Rn in soil gas, and 74 of soil permeability, a significant addition to the existing similar data. The data are analysed in relation with soil texture, geological units and indoor radon risk. There is no clear correlation between radium in soil and indoor radon risk, the most important factor of risk being soil permeability.

URANIUM IN SOIL AND GAMMA DOSE RATE AS PROXIES FOR THE INDOOR RADON RISK: SITUATION IN BELGIUM.

Radon risk maps are usually based either on indoor radon data, or on measurements of soil gas radon and soil permeability. If these data are not available or not sufficient, it was suggested that other data could be used as an approximate substitute (a proxy) to the missing information, like the concentration of 238U or 226Ra in soils or the terrestrial gamma dose rate (TGDR). We examine here the correlation between airborne measurements of soil U and indoor radon, and between airborne U and TGDR, and their link with affected/unaffected areas. No clear correlation is found between airborne U and affected areas, as strongly affected areas are not characterised by a higher U level. Only the moderately affected area of Condroz can be connected to a higher U level, related to a few U anomalies. TGDR shows a rather good correlation with airborne U, but its relation with radon risk is less clear. Soil uranium and TGDR may help to screen out areas with very low U and very low TGDR, which have a low indoor radon risk, but they cannot be considered as good proxies for predicting radon-affected areas in Belgium.

High radon areas in the Walloon region of Belgium.

Indoor radon data from Southern Belgium are organised in 35 geological units (GUs), most of which are homogeneous with respect to the radon risk. The percentage of cases above the reference level (400 Bq m(-3); 300 Bq m(-3) in the future) is calculated for these GUs from the observations and from the log-normal distribution fitted to the data. Affected areas are defined as areas with more than 1 % of houses above the reference level. In the north of the region, the old Palaeozoic basement is generally covered by Silesian, Cretaceous and Tertiary rocks, which are unaffected. The affected areas here are hot spots associated with specific Palaeozoic outcrops. In the south, there is generally no cover above Palaeozoic formations, which are often radon affected. The affected areas of Ardenne and Condroz dominate this part, but unaffected areas occur like Famenne and Gaume. About 48 % of the Walloon region is expected to be radon affected.

Gamma spectrum unfolding for a NaI monitor of radioactivity in aquatic systems: experimental evaluations of the minimal detectable activity.

This paper deals with the experimental evaluation of the minimal detectable activity achievable by unfolding the gamma spectra of a NaI monitor. An aquatic monitor initially developed by the Institut des Radio-Eléments (IRE) is used for the application. Unfolding of the spectra is performed with GRAVEL, a UMG package code, on the basis of a response matrix obtained with MCNP5.1.40. Experimental data have been measured at IRE, in a 20m(3) seawater tank, for known activities of (137)Cs mixed with other gamma emitters ((40)K, (133)Ba, (113)Sn and (139)Ce). Deconvolution allows one to reduce the MDA of (137)Cs by an order of magnitude.

Indoor radon measurements in the city of Valencia.

The indoor radon risk in Valencia (Spain) was studied more than twenty years ago in two surveys using different methodologies and leading to contradictory results. We report here on new indoor radon measurements with the charcoal canister technique, which confirm the low average level of indoor radon in the city, with a geometrical mean of 24 Bq/m(3) and an arithmetic mean of 27 Bq/m(3).

Neutron-photon discrimination and spectrum unfolding with a stilbene detector.

As a first step into the development of a neutron dose monitor, a stilbene detector is used to test a procedure applicable to other organic scintillators allowing for neutron-photon discrimination. The pulses are measured by numerical acquisition and their amplitude and decay time are calculated by software. The discrimination is performed in an amplitude-decay time plot, and separate amplitude spectra are built. These spectra are unfolded MAXED, using the detector response matrices calculated with MCNPX.

Gamma spectrum unfolding for a NaI monitor of radioactivity in aquatic systems.

Spectrum unfolding is a powerful method that can enhance the readability of experimental energy spectra obtained by detectors of poor resolution. It is applied to the NaI-based monitor. The UMG 3.3 package is used for unfolding the experimental spectra with the response matrix obtained by MCNP4c2. The main parameter influencing the quality of the results is the chi(2). The goal of this study is to optimize the choice of this factor. The statistical accuracy of the technique is evaluated.

Indoor radon in the region of Brussels.

The indoor radon (222Rn) concentration has been measured by charcoal detectors in 278 buildings in the region of Brussels, Belgium. The correlation with the nature of the subsoil can be studied in detail thanks to the available geotechnical map. With a geometrical mean indoor radon concentration of 19 Bq m(-3), Brussels can be considered as generally unaffected by the radon problem. No value higher than 400 Bq m(-3) (the EU reference level for existing houses) was measured in an occupied room. However, two factors that may enhance the risk are identified: the absence of a basement or a ventilated crawl space, and the presence of loess, under the house. About one third of the houses without basements or ventilated crawl spaces built on loess show an indoor radon concentration above 200 Bq m(-3) (the EU reference level for new houses).

Geological controls to the indoor radon distribution in southern Belgium.

Soils and rocks are the predominant source of indoor radon (Rn) in southern Belgium. We have studied the correlations between geological features and indoor Rn concentrations using an indoor Rn data set of approx. 1700 short-term measurements. The sediments in the study region are divided into 11 geological series or 43 stages and 16 rock types. The results show a striking relation between indoor Rn concentration and the geological factors.

Interaction of caffeine with the DNA of Chinese hamster cells.

Incubation of Chinese hamster cells with labelled caffeine leads to transfer of radioactivity to DNA. This association occurs during the S phase of the cell cycle and involves parental as well as newly synthesised strands. The replacement of thymidine by BrdUrd prevents the incorporation radioactivity from caffeine into the DNA strands containing BrdUrd. Thymine is the only base which becomes labelled and data suggesting the participation of methyl groups of caffeine in the biosynthesis of thymine are presented. Ultraviolet irradiation increases the incorporation of radioactivity from caffeine to DNA.

The activation of sodium-plus-potassium ion-dependent adenosine triphosphatase from marine teleost gills by univalent cations.

The apparent affinity constants for the binding of Cs+, Rb+, K+, Li+, Tl+ and NH4+ to (Na+ + K+)-dependent adenosine triphosphatase from teleost gills were measured and the values discussed in terms of the ion-selectivity isotherm described by Eisenman & Krasne (1975) [in MTP International Review of Science: Biochemistry Series One (Fox, C.F., ed.), vol. 2, pp. 27--59, Butterworths University Park Press, Baltimore]. The ion selectivity of the present enzyme is remarkably similar to that from nerve and brain.