The Bacau (Romania) phosphogypsum stacks as a source of radioactive threat: a case study.

For a detailed characterization of the 5.7 106 mt phosphogypsum (PG) stack in the vicinity of Bacau city, Romania, the air dose rate (ADR) was measured in 72 points covering the stack surface, while 10 samples of stack material were collected for future analysis. Radiometric determinations showed for the ADR values varying between 364 ± 53 and 489 ± 8 nSv/h, with some extreme values of 2775 ± 734 nSv/h, significantly exceeding 90 nSv/h, the average value reported for the Romanian territory. High-resolution gamma-ray spectroscopy (HRGS), performed on 10 samples collected from the entire PG stack evidenced only the presence of 226Ra as the major radioactive element with a specific activity varied between 820 ± 150 and 5278 ± 264 Bq/kg for hot spots. Further analysis performed on a similar number of samples by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX), evidenced, beside gypsum as the main component, traces of brushite (CaHPO4·2H2O) and ardealite (Ca2(PO3OH)(SO4)·4H2O), as well as the presence of small acicular celestine (SrSO4) agglomerates. XRF determinations of the mass fractions of major elements evidenced values such as SiO2 (2.31 ± 0.73 %), TiO2 (0.07 ± 0.01 %), Al2O3 (0.17 ± 0.04 %), Fe2O3 (0.87 ± 0.18 %), MnO (0.01 ± 0.01 %), MgO (0.17 ± 0.02 %), CaO (32.5 ± 0.82 %), Na2O (0.04 ± 0.04 %), K2O (0.05 ± 0.01 %), P2O5 (2.12 ± 0.51 %), LOI (20.2 ± 0.3 %), i.e. closer to literature reported data for PG of different provenience while the data concerning the distribution of 20 trace elements, including incompatible Sc, La, Ce, and Th were relatively closer to the upper continental crust (UCC).

The distribution of natural radionuclides 40K, 228Ac, and 226Ra on Romanian Territory: a radiometric study.

To estimate the radiation hazard due to the natural terrestrial radioactivity, 598 samples of soil covering the entire Romanian territory were collected and analyzed for the distribution of natural radionuclides 40K, 228Ac, and 226Ra. The ultra-low background Slanic-Prahova underground laboratory was used to determine the gamma-ray-specific activity of these radioactive isotopes with an uncertainty between 5 and 20%. All these data permitted to establishing a set of 2D maps illustrating the distribution of specific activity of each radionuclide as well as of the resulting air dose rate, all of them illustrating an heterogeneous distribution, increased values being displaced on the western and south-western territory. Mediated over 598 points, these determinations led to a value of annual effective dose of 0.7 ± 0.15 mSv/y and an external hazard index of 0.46 ± 0.1, both attesting to a radioecologically safe environment for human activity.

137Cs distribution on the territory of Romania 30 years after Chernobyl accident.

To estimate the contribution of Chernobyl 137Cs contamination, in 1993 and especially 2016, its total inventory was determined by gamma-ray high-resolution spectroscopy in 62 and respectively 747 soil samples covering the entire Romanian territory. This permitted to estimate the 137Cs inventory as varying between 0.4 and 187 as well as between 0.2 and 94.2 kBq/m2 for years 1993 and 2016, respectively. By representing the spatial distribution of 137Cs inventory in Voronoi polygons, it was possible to evidence a decrease of the total 137Cs inventory over entire Romanian territory with a factor of about 3 from about 3.6 TBq to less than 1.2 TBq, exceeding in this way the natural decay which suggests that a certain amount of 137Cs was washed out by precipitation and, at a lower extent, was incorporated into plants. At the same time, by evaluating the maximum contribution of 137Cs to the population exposure, in 1993 as well as in 2016, the supplementary annual effective dose did not exceed, in the majority of sampling points the value of 0.2 mSv/year.

Radiometric, SEM and XRD investigation of the Chituc black sands, southern Danube Delta, Romania.

The black sand of the Chituc marine sand bank, northern of the city of Navodari (Romania), presents anomalous high radioactivity. Field measurements recorded in some places dose rate up to 200 nSv/h, significantly overpassing the average value of 44 ± 20 nSv/h along the entire Southern sector of Romanian Black Sea shore. Gamma ray spectrometry performed on both Slanic-Prahova Underground Low Background Laboratory and Geological Institute of Romania Radiometric Facilities showed with clarity the dominance of (228)Ac radioisotope in the 50 microns fraction together with the (226)Ra and traces of (40)K. No significant amount of anthropogenic (137)Cs was identified. Based on radiometric as well as on SEM-EDAX and XRD determinations we come to the conclusion that the evidenced radioactivity could be attributed to both uranium and thorium series in the zircon and monazite fractions and to a lesser extent to potassium in the feldspars.