RADIATION EXPOSURE FROM NATURAL RADIONUCLIDES IN BUILDING MATERIALS.

Building materials from Iberian Peninsula (Portugal and Spain) were collected and analysed for 226Ra, 232Th and 40K using HPGe gamma-ray spectrometers. The results show that the highest mean value of 226Ra and 232Th activities are 2168 and 390 Bq kg-1, respectively, measured in zircon. For 40K, this value is 1290 Bq kg-1, measured in granite. The mean concentrations of the three radionuclides in the different building materials, excluding the zircon and the industrial by-products (ashes, gypsum and phosphogypsum), are 62, 31 and 519 Bq kg-1 for 226Ra, 232Th and 40K, respectively. The radiological health hazard parameters: radium equivalent activity (Raeq), activity concentration index (I) absorbed and effective dose rates, associated with these radionuclides, were evaluated. These values are within the EU recommended limits in building materials, except for same samples of aggregates, granites, ceramics, phosphogypsum and zircon. This study will contribute for the worldwide data pooling on the radioactivity of the building materials.

Redistribution of Cs 137 introduced into montmorillonite in association with organic matter coming from biomass composting.

The adsorption and later bioavailability of 137Cs from the system humic acid (HA)/humic acid like compounds (HALC) and montmorillonite was investigated. The setup of the experiments should approach as much as possible natural conditions when 137Cs is introduced into soil with HALC from decomposed biomass. The significant differences were found in the trials containing various HA/HALC and also pure montmorillonite. The 137Cs was more available when it reached soil in association with HALC originated from compost than when it was adsorbed on stable humic acids. Moreover, the long term interaction of 137Cs with HALC led to decrease of 137Cs adsorbed on montmorillonite and increase of its bioavailable fraction. UV-Vis spectrometry and infrared spectroscopy showed the clear difference between HA, fresh HALC and old HALC which could partially explain the different results.

ASSESSMENT OF RADIUM ACTIVITY CONCENTRATION AND RADON EXHALATION RATES IN IBERIAN PENINSULA BUILDING MATERIALS.

Radium (226Ra) is a natural radioactive element of the uranium decay series, which could also be present in building materials. Radon (222Rn) is continuously produced by the decay of 226Ra and its presence inside buildings can contribute to the increase of the population exposure to ionizing radiation. In this work, the amount of radium activity concentration and radon exhalation rates in several types of building materials that are commonly used in the Iberian Peninsula have been tested. The radium activity concentration was measured by gamma-ray spectrometry, whereas the radon exhalation rates were carried out using a continuous radon monitor (active measuring technique) and a solid state nuclear track detectors (passive measuring technique). The 226Ra mean values range from 5.0 to 123.4 Bq kg-1. As expected, the results show that the radon exhalation rate is higher in granites samples relatively to others building materials analysed. A positive correlation was found between radium activity concentration and radon exhalation rates in both techniques. The emanation fraction and alpha index were also calculated.

Development of a couple of methods for measuring radon exhalation from building materials commonly used in the Iberian Peninsula.

Radon is considered to be the main contributor to the worldwide population exposure to natural sources of radiation and so a lot of efforts have been made in most countries to assess indoor radon concentrations. Radon exhales from the earth's surface and is part of the radioactive decay series of uranium, which is also present in building materials. In this work, measurements of radon exhalation rates in building materials commonly used in the Iberian Peninsula have been carried out by using two different methods: active and passive techniques. In the first technique, the radon exhalation rate was measured following the radon activity growth as a function of time, by using a continuous radon monitor. The second technique is based on integrated measurements by using solid-state nuclear track detectors and a Spark Counter reading equipment. The results obtained by both measuring methods were found to be consistent.

The influence of particle size on radionuclide activity concentrations in Tejo River sediments.

Sediment samples from Tejo River were analyzed for (228)Ra, (226)Ra, (137)Cs and (40)K by HPGe gamma spectrometry. The activity concentration data were statistically analyzed. The activity concentrations values were in the range of about two orders of magnitude for each radionuclide. The influence of the particle size on the radionuclide concentrations was observed. The different environmental origins of the radionuclides (228)Ra, (226)Ra, (137)Cs and (40)K, in the sediments were demonstrated through correlation analysis. Cluster analysis showed a close relationship between (228)Ra and (226)Ra and a different behavior for (40)K. The data obtained in this study provides useful information on the background radioactivity of the studied area and can be further used for radiological mapping of the Tejo River.

Quality control assurance of strontium-90 in foodstuffs by LSC.

A method based on the separation of Sr-90 by extraction chromatography and beta determination by Liquid Scintillation Counting (LSC) technique was used for strontium analysis in food samples. The methodology consisted in prior sample treatment (drying and incineration) followed by radiochemical separation of Sr-90 by extraction chromatography, using the Sr-resin. The chemical yield was determined by gravimetric method, adding stable strontium to the matrix. Beta activity (Sr-90/Y-90) was determined using a low background liquid scintillation spectrometer (Tri-Carb 3170 TR/SL, Packard). The accuracy and the precision of the method, was performed previously through recovery trials with Sr-90 spiked samples, using the same type of matrices (milk, complete meals, meat and vegetables). A reference material (IAEA_321) was now used to measure the accuracy of the procedure. Participation in interlaboratory comparison exercises was also performed in order to establish an external control on the measurements and to ensure the adequacy of the method.

Environmental radioactivity monitoring in Portugal.

Environmental radioactivity monitoring in Portugal is a nationwide programme that consists of two complementary (sparse and dense) sampling networks established following the EURATOM recommendations [2000/473/EURATOM-Commission Recommendation of 8 June 2000, Official Journal of the European Commission, no. 191, 27 June 2000]. This paper describes the aim of the monitoring programme, how it was implemented, the sampling locations, the type of samples, the analytical and measurement methods and the quality control programmes. Some representative results are also discussed. Based on the monitoring data it can be concluded that the Portuguese population has not been exposed to radioactivity levels that require any radiological protection measures.

Radioactivity in the environment around past radium and uranium mining sites of Portugal.

Measurements of ambient radiation doses and determination of radionuclide concentrations in mining waste and soils were performed in 60 areas of former radium and uranium mining. In several places, mining waste and low-grade uranium ore left on the surface contain radioactivity above regional background. Most of the former mining sites present no enhanced radionuclide concentrations. However, in the mining facilities where the radioactive ore was chemically extracted, mill tailings contain materials with elevated levels of radioactivity, up to 200 times the levels in unaffected soils of the region. Mud from neutralization ponds used to treat acid mine waters contains also elevated radionuclide concentrations. Furthermore, depending on the type of waste, the radioelement composition varies. Environmental rehabilitation measures shall take these differences into account in order to prevent in the long term the radioactive contamination of agriculture soils and water resources, and to ensure adequate radiological protection to the public and to the environment.

The "AQUASCOPE" simplified model for predicting 89,90Sr, 131I, and 134,137Cs in surface waters after a large-scale radioactive fallout.

Simplified dynamic models have been developed for predicting the concentrations of radiocesium, radiostrontium, and I in surface waters and freshwater fish following a large-scale radioactive fallout. The models are intended to give averaged estimates for radionuclides in water bodies and in fish for all times after a radioactive fallout event. The models are parameterized using empirical data collected for many lakes and rivers in Belarus, Russia, Ukraine, UK, Finland, Italy, The Netherlands, and Germany. These measurements span a long time period after fallout from atmospheric nuclear weapons testing and following the Chernobyl accident. The models thus developed were tested against independent measurements from the Kiev Reservoir and Chernobyl Cooling Pond (Ukraine) and the Sozh River (Belarus) after the Chernobyl accident, from Lake Uruskul (Russia), following the Kyshtym accident in 1957, and from Haweswater Reservoir (UK), following atmospheric nuclear weapons testing. The AQUASCOPE models (implemented in EXCEL spreadsheets) and model documentation are available free of charge from the corresponding author.

226Ra bioavailability to plants at the Urgeiriça uranium mill tailings site.

Large amounts of solid wastes (tailings) resulting from the exploitation and treatment of uranium ore at the Urgeiriça mine (north of Portugal) have been accumulated in dams (tailing ponds). To reduce the dispersion of natural radionuclides into the environment, some dams were revegetated with eucalyptus (Eucalyptus globolus) and pines (Pinus pinea). Besides these plants, some shrubs (Cytisus spp.) are growing in some of the dams. The objective of this study is to determine the 226Ra bioavailability from uranium mill tailings by quantifying the total and available fraction of radium in the tailings and to estimate its transfer to plants growing on the tailing piles. Plant and tailing samples were randomly collected and the activity concentration of 226Ra in plants (aerial part and roots) and tailings was measured by gamma-spectrometry. The exchangeable fraction of radium in tailings was quantified using one single step extraction with 1 mol dm-3 ammonium acetate (pH = 7) or 1 mol dm-3 calcium chloride solutions. The results obtained for 226Ra uptake by plants show that 226Ra concentration ratios for eucalyptus and pines decrease at low 226Ra concentrations in the tailings and appear relatively constant at higher radium concentrations. For shrubs, the concentration ratios increase at higher 226Ra solid waste concentrations approaching a saturation value. Percentage values of 16.0 +/- 8.3 and 12.9 +/- 8.9, for the fraction of radium extracted from the tailings, using 1 mol dm-3 ammonium acetate or calcium chloride solutions, respectively, were obtained. The 226Ra concentration ratios determined on the basis of exchangeable radium are one order of magnitude higher than those based on total radium. It can be concluded that, at a 95% confidence level, more consistent 226Ra concentration ratios were obtained when calculated on the basis of available radium than when total radium was considered, for all the dams.