A practical and general methodology for efficiency calibration of coaxial Ge detectors

The correct determination of artificial and natural radionuclides like 152Eu, 137,134Cs, 60,57Co, etc., and 234,228Th, 228,226Ra, 210Pb and 40K, respectively, is essential for many environmental science fields. For this, a general function was obtained for the full-energy peak efficiency (FEPE) by gamma-ray spectrometry using coaxial Ge detectors. Then, the experimental FEPE values, obtained fixing the energy, Eγ, were fitted varying the thickness, h, of cylindrical standards. The parameters resulted from these fittings were fitted, in turn, versus Eγ, obtaining a general efficiency function, εc (Eγ, h). εc (Eγ, h) was validated, obtaining very good zscore, except for Eγ affected by TCS effects. Consequently, a practical and general method was developed, recalibrating the detector by varying the sample-detector distance, d. εc (Eγ, h, d) was obtained, achieving very good zscore. Furthermore, this practical method was also employed to correct high self-absorptions and high dead times.This research has partially funded by the projects of the Regional Government of Andalusia called “Basic processes regulating the fractionations and enrichments of natural radionuclides under acid mine drainage conditions” (Ref.: UHU-1255876), and “Treatment of acid leachates from phosphogypsum piles located at Huelva, and transport modelling of the released radionuclides” (Ref.: P20_00096), the project funded by the Spanish Ministry of Science, Innovation and Universities’ Research Agency “Development and optimization of a process for removing natural radionuclides in phosphogypsum leachates” (Ref.: PID2020-116461RB-C21), and the Project for Novel Principal Investigators “Quantitative study of the variables involved in the radonexhalation rate for granular solids; application to rafts of granular solid phosphogypsum” (Ref.: UHUPJ-00005-632). The authors acknowledge the funding for open access charge provided by Universidad de Huelva/CBUA

A new efficiency calibration methodology for different atmospheric filter geometries by using coaxial Ge detectors

The study of the different pollutants present in atmospheric aerosols such as trace elements and radionuclides is essential to assess the air quality. To analyze the particulate matter (PM), atmospheric filters with different dimensions and geometries (rectangular, circular, slotted, and square filters) are usually employed. Regarding the pollutants existing in atmospheric aerosols, radionuclides are usually analyzed due to their multiple applications such as either in the environmental radiological control or as tracers of atmospheric processes. Therefore, this study aims to develop a new and general methodology to calibrate in efficiency coaxial Ge detectors to properly determine radionuclides present in the PM by gamma-ray spectrometry for several filter types. For this, granular certified reference materials (CRM) containing only natural radionuclides (²³⁸U-series, ²³²Th-series, and ⁴⁰ K) were selected. Several granular solid CRMs were chosen allowing us to reproduce the same PM deposition geometry and to assure the homogeneity of the added CRMs. These are the main advantages in relation to the typical methods that use liquid CRMs. Furthermore, for filters whose surfaces are relatively large, they were cut in several pieces and placed one on top of the other, achieving the same geometry than the PM deposited onto the filter. Then, the experimental full-energy peak efficiencies (FEPEs) were obtained for each energy of interest (Eγ) and they were fitted versus Eγ, finding a general FEPE function for each filter type. Finally, this methodology was validated for both natural and artificial radionuclides (from 46 to 1332 keV) by using different filter types employed in proficiency test exercises, obtaining |zscore|< 2 for all cases.Funding for open access publishing: Universidad de Huelva / CBUA This research has partially funded by the projects of the Regional Government of Andalusia called “Treatment of acid leachates from phosphogypsum piles located at Huelva, and transport modelling of the released radionuclides” (Ref.: P20_00096) and “Valorization of inorganic wastes enriched in natural radioactivity for sustainable building materials” (Ref.: FEDER-UHU-202020); the project funded by the Spanish Nuclear Safety Council (CSN) “Radon exhalation from building materials; radiological impact and corrective measures” (Ref.: SUBV-4/2021); the project funded by the Spanish Ministry of Science, Innovation and Universities’ Research Agency “Development and optimization of a process for removing natural radionuclides in phosphogypsum leachates” (Ref.: PID2020-116461RB-C21); and the Project for Novel Principal Investigators “Quantitative study of the variables involved in the radon exhalation rate for granular solids; application to rafts of granular solid phosphogypsum” (Ref.: UHUPJ-00005–632)

External occupational exposures in some NORM industries located at the south-west of Spain

Detailed mappings of the external exposures which can be received by the workers in two NORM industrial factories located at the South-West of Spain have been performed: one devoted to the production of phosphoric acid, and the other devoted to the production of titanium dioxide pigments. In most places of the analyzed factories, the external exposures are moderated, although in some specific points, and associated to the presence of scales, their values are clearly higher. Nevertheless, under normal running conditions, the contribution of the external exposures to the effective doses received by the workers is lower than 1 mSv/y because the worker occupancy factors values are very low in the places with the highest external exposures

Tidal circulation, sediment and pollutant transport in Cádiz Bay (SW Spain): A modelling study

A numerical model to simulate the dispersion of particle-reactive tracers in Cádiz Bay (SW Spain) has been developed. It includes a hydrodynamic submodel to provide water currents, a sediment transport submodel, which provides suspended matter concentrations and sedimentation rates and the pollutant dispersion model. Pollutant exchanges between the liquid and solid phases are described in a dynamic way, using kinetic transfer coefficients. Results of the hydrodynamic and sediment transport models have been compared with observations. The contamination of sediments of the bay by fallout 137Cs has been simulated. The existence of an accumulation area in the inner bay, found in field measurements, has been reproduced by the model. Dispersion experiments for Zn and 226Ra have also been carried out. Flushing times of the inner bay have been finally determined through numerical experimentsMinisterio de Ciencia e Innovación CTM2009-14321-C02-01Ministerio de Ciencia e Innovación CTM2009-14321-C02-0

Radioactive impact in sediments from an estuarine system affected by industrial wastes releases

A big fertilizer industrial complex and a vast extension of phosphogypsum piles (12 km2), sited in the estuary formed by the Odiel and Tinto river mouths (southwest of Spain), are producing an unambiguous radioactive impact in their surrounding aquatic environment through radionuclides from the U-series. The levels and distribution of radionuclides in sediments from this estuarine system have been determined. The analyses of radionuclide concentrations and activity ratios have provided us with an interesting information to evaluate the extension, degree and routes of the radioactive impact, as well as for the knowledge of the different pathways followed for the radioactive contamination to disturb this natural system. The obtained results indicate that the main pathway of radioactive contamination of the estuary is through the dissolution in its waters of the radionuclides released by the industrial activities and their later fixation on the particulate materials. Tidal activity also plays an important role in the transport and homogenization along the estuary of the radioactivity released from the fertilizer plants. D 2002 Elsevier Science Ltd. All rights reserved.Junta de Andalucia (España) project 1FD97-0900-C02-02 (AMB

The geochemical behavior of natural radionuclides in coastal waters: A modeling study for the Huelva estuary

A numerical model to study the behavior and distribution of natural radionuclides in sediments of an estuary (Odiel and Tinto rivers, SW Spain) affected by acid mine drainage and industrial activities has been developed. The model solves water circulation due to tides and river stream flows. The dispersion model includes uptake/ release reactions of radionuclides between the dissolved phase and bed sediments in a dynamic way, using kinetic transfer coefficients. Seasonal pH and chlorinity distributions are simulated, and a formulation has been developed to consider these seasonal variations on kinetic coefficients. Calculated concentrations of 226Ra and 238U in sediments have been compared with measurements from four seasonal sampling campaigns. Numerical experiments have been carried out to study the relative significance of the different radionuclides sources into the estuary as well as the effect of the two components of water circulation (tides are river flows) on radionuclide dispersion patterns.Ministerio de Ciencia e Innovación CTM2009-14321-C02-01Junta de Andalucía RNM-630

An upgraded lab-based method to determine natural γ-ray emitters in NORM samples by using Ge detectors

The regulation existing on NORM activities requires the accurate and quick measurement of natural radionuclides in a wide range of matrices by gamma spectrometry. The aim of this work has been to develop a comprehensive and accurate methodology to determine natural long-lived radionuclides (210Pb, 228,226Ra, 234,228Th and 40K) by gamma spectrometry with Ge detectors in NORM samples. An exhaustive calibration method to obtain the full-energy peak efficiency (FEPE), for each gamma emission energy, as a function of the thickness, apparent density and matrix composition of the cylindrical sample, has been developed. The selected certified calibration standards contain only natural radionuclides belonging to the 238U- and 232Th-series as well as 40K (codes RGU-1, RGTh-1 and RGK-1 from IAEA). Then, the obtained FEPE curves were validated using Genie 2000 simulations and Certified Reference Materials, for which the self-attenuation corrections were considered. Finally, a study on 222Rn losses was done for several samples.Funding for open access charge: Universidad de Huelva / CBU

Analysing the performance of radiological monitoring network during nuclear accidents

JRODOS was used to simulate the dispersion of airborne radioactive material from a point source over the period 2012–2015. In total, 1331 radioactive plumes were simulated with the objective to investigate the influence of changes in meteorological conditions in the performance of the monitoring network. For this purpose, the existing set of 84 monitoring stations included in the EUropean Radiological Data Exchange Platform (EURDEP) system in an area of 200 km around the source point is taken as reference. A methodology is presented for quantitative evaluation of the variability of the number of stations affected, the time of the first detection, the maximum registered and differences between the maximum values match in the network and in the simulated plumes. The results show seasonal differences in all of these parameters according to changes in the size and shape of the affected area due to meteorological conditions. There are large differences in the number of monitoring stations affected by the plumes, from 2 to 74; in the timing and location of the first alert given by the network, from 1 to more than 5 h and faster along the west-east axis from the source; and in level of maximum gamma dose rate detected by the monitoring stations, from 0.17 nSv/h in summer to 0.22 nSv/h in autumn. These results show the need to consider this type of analysis over the years in the design of monitoring networks and in the development of nuclear emergency preparedness and response (EP&R) plans

A method for the measurement of 99Tc by Quadrupole ICP-MS in dry fallout and sea grass samples

A method for the detection of "Tc by ICP-MS in environmental samples is proposed and explained in detail. This method combines the capabilities of anion exchange chromatographic TEVA-Spec' resin with prior isotope concentration using solvent extraction to Tn'butylphosphate. The problem that the excess of Mo in the solution analyzed by ICP-MS causes in the instrumental response at m/z ratio 99 is described in detail, and the proposed solution takes the form of the referred radlochemical method. The realistic limits of detection of this technique (bearing in mind the particular methodology here applied) are in the range of 20-70 mBq/kg when treating mass amounts in the range of 20-125 g dry weight. A few environmental samples proceeding from a region unaffected by any closer nuclear industry (the Southwest of Spain) are analyzed for checking '9Tc concentration