PSCF and CWT methods as a tool to identify potential sources of 7Be and 210Pb aerosols in Granada, Spain.

This research is focused on studying the preferred source regions and the pathways of the air masses with high particulate concentrations impacting on the activity concentrations of 7Be and 210Pb aerosols in Granada atmosphere. For this purpose, three different source-receptor methods have been used: Cluster Analysis, Potential Source Contribution Function (PSCF), and Concentration Weighted Trajectory (CWT). Air filter samples were weekly collected and analysed in Granada university (Spain 37.177N, 3.598 W, 687m a.s.l.) during 12 years (2006-2017) for the activity concentration of 7Be, and during 5 years (2010-2014) for the one of 210Pb. The time series of the collected data indicate that the concentration of both radiotracers present a cyclical and seasonal pattern, in association with their origins and atmospheric conditions. Clustering analysis showed that the air masses arriving to Granada can be classified as: (1) tropical continental air masses coming from the Mediterranean Sea, (2) tropical and warm polar maritime air masses produced over the Atlantic Ocean, and (3) continental air masses originated over Europe and Northern Africa. The PSCF and CWT methods confirmed that the main source areas of 7Be are located in the Atlantic coast of southern Morocco, and Northern Africa. On the other hand, southern France and the Algerian desert were found to be the main region sources of 210Pb. In addition, the Mediterranean Basin has been postulated as a strong source region for 7Be and 210Pb. Furthermore, the PSCF and CWT models show that the regions with larger 7Be/210Pb ratios are located in the Atlantic Ocean, due to frequent stratospheric intrusions specially during the winter months.

Neutronic study of the 2-MW TRIGA MARK-II research reactor by the deterministic codes DRAGON5 & DONJON5.

The main objective of this work is to perform a neutronic study of the 2 MW TRIGA MARK-II research reactor of the National Centre of Sciences, Energy and Nuclear Techniques (CNESTEN), Rabat, Morocco and then validate the results by comparing the experimental values and those published for an ordinary 2 MW TRIGA MARK II research reactor. The core diffusion code DONJON5 and the lattice code DRAGON5 were coupled to perform a full model of the TRIGA core and their consistency and accuracy were established by benchmarking the TRIGA experiments. In this study, the nuclear data libraries ENDF/B-VII.1 and JEFF3.1 based on 172 energy groups were used. The group constants of all the reactor components were generated using DRAGON5 code and the collision probability method. These group constants were used then in the DONJON5 core code to calculate the multiplication factor, core excess reactivity, total and integral control rods worth as well as power peaking factors. Good agreement found between the calculated and measured results.

Modeling and simulation of a TRIGA MARK-II research reactor using WIMSD-5B and CITATION codes.

The main objective of this study is to analyse neutronic safety parameters of the Moroccan TRIGA Mark-II research reactor using the WIMSD-5B and CITATION computer codes. New 172-group libraries of multi-group constants for the lattice code WIMSD-5B have been generated for all isotopes presented in the TRIGA reactor core by processing nuclear data from ENDFB-VII.1, JENDL-4.0 and JEFF-3.1.1 using NJOY99. The lattice code WIMSD-5B was employed to generate multi-group cross sections in the suitable format that will be used by the 3-dimensional diffusion code CITATION. This later was used to calculate various neutronic safety parameters of the TRIGA Mark-II research reactor, such as reactivity excess and neutron fluxes profiles. The results of these calculations are compared to the results of Monte Carlo calculation based on MCNP code. A good agreement is achieved and the current computation scheme will be adopted for our further coupling neutronic/thermal-hydraulic study of the Moroccan TRIGA reactor.

7Be spatial and temporal pattern in southwest of Europe (Spain): Evaluation of a predictive model.

This study presents a comprehensive statistical analysis of the cosmogenic radioisotope 7Be measured in surface air in ten stations over Spain for a 9 years period (from January 2006 to December 2014). Besides the analysis of 7Be seasonal and inter-annual variability, 7Be frequency distributions and its correlations with meteorological variables observed in the 10 sampling sites were investigated. The second part of this paper focuses on a feasibility study for the application of the Artificial Neural Networks (ANNs) to predict monthly 7Be activity concentrations using meteorological variables, PM10 concentrations and the sunspot number as input parameters. Notwithstanding the low correlations found between 7Be and input parameter, the performance of the ANNs, as evaluated by the relevant statistical parameters, demonstrates their capability to correctly predict 7Be monthly activities in the 10 Spanish sampling sites.

Impact of air masses on the distribution of 210Pb in the southeast of Iberian Peninsula air.

The current research has been developed in the southern of the Iberian Peninsula in order to better understand the atmospheric processes and also the influence of the air masses origin and pathways in the transport of 210Pb-aerosols in the atmosphere. Simultaneous measurements of the radionuclides 7Be and 210Pb on airborne have been routinely carried out at Granada (Spain 37.177N, 3.598 W, 687 m a.s.l.) from 2010 to 2014. The long term monitoring evolution on 210Pb is discussed in this study and also the useful ratio 7Be/210Pb. The maximum monthly activity concentration for 210Pb at ground level in Granada was detected during summer and early autumn (September), whereas minimum activity was measured in the winter. The monthly mean activity concentration for 210Pb was 617.8 ± 33.0 µBq·m-3. The results show that the annual average 210Pb concentrations in samples collected during the same period were almost constant. The lowest activity concentration for 210Pb are associated with maritime air masses coming from Atlantic and Norwest of Spain, while the highest activity concentrations for this radiotracers were positively correlated with the arrival of mineral dust linked to continental air masses coming from Mediterranean, Africa and Local area. The concentrations values show a nice agreement with the relevant reported results.

Neutronic and thermal-hydraulic analysis of new irradiation channels inside the Moroccan TRIGA Mark II research reactor core.

This study was conducted to improve the capacity of radioisotope production in the Moroccan TRIGA Mark II research reactor, which is considered as one of the most important applications of research reactors. The aim of this study is to enhance the utilization of TRIGA core in the field of neutron activation and ensure an economic use of the fuel. The main idea was to create an additional irradiation channel (IC) inside the core. For this purpose, three new core configurations are proposed, which differ according to the IC position in the core. Thermal neutron flux distribution and other neutronic safety parameters such as power peaking factors, excess reactivity, and control rods worth reactivity were calculated using the Monte Carlo N-Particle Transport (MCNP) code and neutron cross-section library based on ENDF/B-VII evaluation. The calculated thermal flux in the central thimble (CT) and in the added IC for the reconfigured core is compared with the thermal flux in the CT of the existing core, which is taken as a reference. The results show that all the obtained fluxes in CTs are very close to the reference value, while a remarkable difference is observed between the fluxes in the new ICs and reference. This difference depends on the position of IC in the reactor core. To demonstrate that the Moroccan TRIGA reactor could safely operate at 2MW, with new configurations based on new ICs, different safety-related thermal-hydraulic parameters were investigated. The PARET model was used in this study to verify whether the safety margins are met despite the new modifications of the core. The results show that it is possible to introduce new ICs safely in the reactor core, because the obtained values of the parameters are largely far from compromising the safety of the reactor.

A cluster analysis of back trajectories to study the behaviour of radioactive aerosols in the south-east of Spain.

This research is focused on the study of the influence of the air masses together with the local meteorological fluctuations on the amount of radioactive elements in aerosols at surface air of the southeastern of Iberian Peninsula. The radioactivity in aerosols has been determined by measuring the concentration activity of Gross ß and (7)Be from January 4(th), 2011 to December 31(s)(t), 2013. The activity concentration (Bq/m(3)) of gross beta was measured by α/ß Low-Level counter, whereas the activity concentration of (7)Be (Bq/m(3)) was detected by gamma spectrometry (Eγ = 477.6 KeV, Yield = 10.42%). The air mass origings have been set using k-means clustering analysis of daily 72-h kinematic 3D backward trajectories at 500 m, 1500 m and 3000 m of altitude. Finally, a multiple Regression Analysis (MRA) have been carried out in order to determine the influence of the origins and trajectories of the air masses and local meteorology variations on the evolution of Gross ß and (7)Be activity concentration. In conclusion, the results of the current research demonstrate that the re-suspended mineral dust from Northern Africa transported by Mediterranean air masses at low altitude (500 m) and African air masses at high altitude (3000 m) increases the radioactivity concentration in aerosols at the surface atmosphere. In addition, the opposite influence of the Saharan intrusions at 1500 m of altitude on the behaviour of (7)Be aerosols deserves special attention.

Monte Carlo analysis of the influence of germanium dead layer thickness on the HPGe gamma detector experimental efficiency measured by use of extended sources.

We have carried out a study to figure out the influence of crystal inactive-layer thickness on gamma spectra measured by an HPGe detector. The thickness of this dead layer (DL) is not known (no information about it was delivered by the manufacturer) due to the existence of a transition zone where photons are increasingly absorbed. To perform this analyses a virtual model of a Canberra HPGe detector was produced with the aid of MCNPX 2.7 code. The main objective of this work is to produce an optimal modeling for our GPGe detector. To this end, the study included the analysis of the total inactive germanium layer thickness and the active volume that are needed in order to obtain the smallest discrepancy between calculated and experimental efficiencies. Calculations and measurements were performed for all of the radionuclides included in a standard calibration gamma cocktail solution. Different geometry sources were used: a Marinelli and two other new sources represented as S(1) and S(2). The former was used for the determination of the active volume, whereas the two latter were used for the determination of the face and lateral DL, respectively. The model was validated by comparing calculated and experimental full energy peak efficiencies in the 50-1900keV energy range. the results show that the insertion of the DL parameter in the modeling is absolutely essential to reproduce the experimental results, and that the thickness of this DL varies from one position to the other on the detector surface.