The issue of natural radioactivity in groundwater is reviewed, with emphasis on those radioisotopes which contribute in a significant way to the overall effective dose received by members of the public due to the intake of drinking water originating from groundwater systems. The term ‘natural radioactivity’ is used in this context to cover all radioactivity present in the environment, including man-made (anthropogenic) radioactivity. Comprehensive discussion of radiological aspects of the presence of natural radionuclides in groundwater, including an overview of current regulations dealing with radioactivity in drinking water, is provided. The presented data indicate that thorough assessments of the committed doses resulting from the presence of natural radioactivity in groundwater are needed, particularly when such water is envisaged for regular intake by infants. They should be based on a precise determination of radioactivity concentration levels of the whole suite of radionuclides, including characterisation of their temporal variability. Equally important is a realistic assessment of water intake values for specific age groups. Only such an evaluation may provide the basis for possible remedial actions.

The field radiometric and laboratory measurements were performed at the Sin Quyen copper deposit in North Vietnam. The field gamma-ray spectrometry indicated the concentration of uranium ranging from 5.5 to 87 ppm, thorium from 5.6 to 33.2 ppm, and potassium from 0.3 to 4.7%. The measured dose rates ranged from 115 to 582 nGy/h, the highest doses being at the copper ore. Concentrations in the solid samples were in the range of 20–1700 Bq/kg for uranium, 20–92.7 Bq/kg for thorium, and 7–1345 Bq/kg for potassium. The calculated doses were from 22 to 896 nGy/h; both measured and calculated dose rates are mostly related to uranium. Concentrations of radium in water samples were below 0.17 Bq/L. Uranium in water samples was significantly higher than the hydrogeological background; the maximum of 13 Bq/L was at the waste zone pool, but neither radium nor uranium were present in tap water. Radon concentration in the dwelling air was from 42 to 278 Bq/m3 for 222Rn and from 8 to 193 Bq/m3 for 220Rn. The estimated committed dose rates were principally related to 222Rn concentration and ranged from 1.1 to 8.1 mSv/y.

A natural radioactivity in thermal water was investigated based on 19 selected thermal waters from Poland. The analysed results show that the radionuclides’ concentrations in the study waters vary over a wide range. The temperature of the waters varies from above 20 °C to above 80 °C. The waters are characterised by different mineralisation, chemical compositions, and belong to different hydrochemical types. There is a good correlation between the water temperature and the depths of the aquifer formations occurrence, suggesting the thermal energy originates from the thermal geogradient. The concentration of radium is well correlated with the water mineralisation. The ratio of radium activity (²²⁶Ra/²²⁸Ra) in groundwater relates not only the ratio of uranium activity to that of thorium (²³⁸U/²³²Th) in aquifer formation, but also depends on the physical and chemical water properties. Based on the concentration of radon and its transport model, the radiation exposures due to inhalation of ²²²Rn and its progeny for employees and clients of the spa were assessed. The use of the thermal waters as a drinking resource may be problematic due to the possibility of exceeding the recommended annual committed effective dose 0.1 mSv.

Natural radioactive nuclides in the thermal waters of the Polish Inner Carpathians: The chemical compositions and activity concentrations of ²³⁸U, ²³⁴U, ²²⁶Ra, ²²⁸Ra and ²²²Rn were measured in the thermal waters occurring in the Podhale Trough. This region, part of the Polish Inner Carpathians, is the artesian basin situated between two groundwater recharging zones, the Tatras to the south and the Pieniny Klippen Belt to the north. The thermal water samples were collected from nine selected boreholes with the depths from 1113 m (Zakopane IG-2) to 5526 m (Bańska Niżna IG-1). The waters belong to four hydrochemical types: HCO₃-SO₄-Ca-Mg-Na, SO₄-HCO₃-Cl-Na-Ca, SO₄-Ca-Na and SO₄-Cl-Ca-Na. Their mineralization and temperature range from several hundreds to 2500 mg/l and 23.9 to 86.3 °C, respectively. Excluding the waters from the Szymoszkowa GT-1 and Chochołów PIG-1 boreholes, the activity concentrations of the uranium and radium isotopes in the waters are relatively low and vary from decimals to above ten mBq/l and from several tens to about 600 mBq/l, respectively. They are classified as radon-poor waters. The phenomena mentioned seem to be characteristic of the waters draining limestone formations overlaying the crystalline rocks, namely the principal aquifers in the Tatras. The significant levels of the uranium and radium activity concentrations in the waters from Szymoszkowa GT-1 and Chochołów PIG-1 can be connected with the presences of Lower Triassic black shales with tuffites rich in uranium in the respective recharge areas. Comparing the parameters of the Podhale thermal waters with those of some selected thermal waters occurring in other regions of Poland and in north-west Croatia, the French Massif Central, Spanish Andalusia and north-east Tunisia, the authors found that the temperature of the thermal waters is contained between 16 and about 100 °C; the mineralization and concentrations of radionuclides vary in broad intervals and are considerably affected by the lithology and the geological structure of the region. The ²²⁶Ra activity concentration exceeds that of ²²⁸Ra in almost each of the thermal waters compared, which is similar to the waters from Podhale.

In the presented paper analysis of sensitivity of self-attenuation correction C _s to the accuracy of chemical composition analysis is presented. The analyses were done by means of Monte Carlo simulation for cylindrical samples and for four sample materials: peat, water, ash and soil. For each of these materials the major elements were selected whose determination in the analysed material is necessary. For the remaining elements threshold levels of their concentration were determined—if expected element concentration in a sample exceeds this value, its determination is indispensable, assuming the accuracy of C _s determination at 3 %.