10-Years assessment of 7Be and 210Pb in atmospheric bulk depositions in Cienfuegos (Cuba).

10-years records of monthly bulk atmospheric fluxes of 7Be and 210Pb (wet + dry, n = 119 samples) at a coastal station in Cienfuegos (Cuba) between 2010 and 2019 were reported and assessed in function of their temporal variability and meteorological influence. Fluxes of 7Be and 210Pb ranged from 120 to 15617 and from 29 to 911 mBq m-2 day-1, respectively. Both radionuclides exhibited a similar seasonal trend with highest values during wet months and minimum values during dry months. The removal of 7Be and 210Pb from the atmosphere was mainly controlled by wet depositions, while dry deposition was estimated to be more important for 210Pb (29% of the total bulk deposition) than for 7Be (12%). The 210Pb/7Be ratios (average of 0.10) showed low variability during wet months with abrupt peaks in the driest months with low temperatures and the highest wind speed and pressure, which was mainly attributed to contributions from soil resuspension. The calculated total deposition velocity of aerosols derived from 7Be (average of 0.48 cm s-1) and 210Pb (average of 0.47 cm s-1) was in agreement with values reported in the literature. Multiple linear regression models for the monthly fluxes of 7Be and 210Pb based on precipitation, temperature and pressure and explaining about 60% of their variances were derived, highlighting the preponderant role of the local and regional conditions on the variability of these radionuclides. The annual fluxes of 7Be (209-1901 Bq m-2 y-1) and 210Pb (35-123 Bq m-2 y-1) were in the range of variations observed in other coastal stations worldwide, showing fluctuations affected by changes in the amount of precipitation during the wet periods. 7Be annual variability also evidenced a significant modulation with the solar activity.

210Pb and 137Cs as tracers of recent sedimentary processes in two water reservoirs in Cuba.

Hanabanilla and Paso Bonito Reservoirs are the main fresh water sources for about half a million inhabitants in central Cuba. Prior to this investigation precise information about the losses of storage capacity was not available. Sedimentation is the dominant process leading to reduction in water storage capacity. We investigated the sedimentation process in both reservoirs by analyzing environmental radionuclides (e.g. 210Pb, 226Ra and 137Cs) in sediment cores. In the shallow Paso Bonito Reservoir (mean depth of 6.5 m; water volume of 8 × 106 m3), we estimated a mean mass accumulation rate (MAR) of 0.4 ± 0.1 g cm-2y-1 based on 210Pb chronologies. 137Cs was detected in the sediments, but due to the recent construction of this reservoir (1975), it was not possible to use it to validate the 210Pb chronologies. The estimated MAR in this reservoir is higher than the typical values reported in similar shallow fresh water reservoirs worldwide. Our results highlight a significant loss of water storage capacity during the past 30 years. In the deeper and larger Hanabanilla Reservoir (mean depth of 15.5 m; water volume of 292 × 106 m3), the MAR was investigated in three different sites of the reservoir. The mean MARs based on the 210Pb chronologies varied between 0.15 and 0.24 g cm-2y-1. The MARs calculated based on the 137Cs profiles further validated these values. We show that the sediment accumulation did not change significantly over the last 50 years. A simple empirical mixing and sedimentation model that assumes 137Cs in the water originated from both, direct atmospheric fallout and the catchment area, was applied to interpret the 137Cs depth profiles. The model consistently reproduced the measured 137Cs profiles in the three cores (R2 > 0.9). Mean residence times for 137Cs in the water and in the catchment area of 1 y and 35-50 y, respectively were estimated. The model identified areas where the catchment component was higher, zones with higher erosion in the catchment, and sites where the fallout component was quantitatively recorded in the sediments.

Monte Carlo simulation of the efficiency response of a well-type HPGe detector at 46.54 keV / Simulación por Monte Carlo de la respuesta en eficiencia de un detector HPGe tipo pozo a la energía de 46.54 keV

In this paper, we used the Monte Carlo simulations method in a well-type HPGe detector using directly the manufacturer supplied data in order to simulate the effi ciency response at 46.54 keV. The efficiency values were calculated as a function of the fi lling height of the sample into the measurement geometry and results were found in good agreement with experimental data. The main deviations were less than 2.5 % with a mean of 0.9 %, which is totally satisfactory for the purposes of environmental samples measurements. We also present a brief discussion about the response of the detector to different values of its geometric parameters.

En el trabajo se utilizaron los métodos de simulación por Monte Carlo en un detector HPGe tipo pozo, usando directamente los parámetros del fabricante para simular la respuesta en eficiencia a la energía de 46.54 keV. Los valores de efi ciencia se calcularon en función de la altura de la muestra en la geometría de medición y los resultados se correspondieron con los valores experimentales. Las mayores diferencias fueron menores que el 2.5 % con un promedio de 0.9 %, lo que es totalmente satisfactorio para la medición de muestras ambientales. Se presentó una breve discusión sobre la respuesta del detector para diferentes parámetros geométrico.

Application of the Monte Carlo efficiency transfer method to an HPGe detector with the purpose of environmental samples measurement.

Monte Carlo efficiency transfer method was used to determine the full energy peak efficiency of a coaxial n-type HPGe detector. The efficiencies calibration curves for three Certificate Reference Materials were determined by efficiency transfer using a (152)Eu reference source. The efficiency values obtained after efficiency transfer were used to calculate the activity concentration of the radionuclides detected in the three materials, which were measured in a low-background gamma spectrometry system. Reported and calculated activity concentration show a good agreement with mean deviations of 5%, which is satisfactory for environmental samples measurement.

Atmospheric deposition patterns of (210)Pb and (7)Be in Cienfuegos, Cuba.

The radiometric composition of bulk deposition samples, collected monthly for one year, February 2010 until January 2011, at a site located in Cienfuegos (22° 03' N, 80° 29' W) (Cuba), are analysed in this paper. Measurement of (7)Be and (210)Pb activity concentrations were carried out in 12 bulk deposition samples. The atmospheric deposition fluxes of (7)Be and (210)Pb are in the range of 13.2-132 and 1.24-8.29 Bq m(-2), and their mean values are: 56.6 and 3.97 Bq m(-2), respectively. The time variations of the different radionuclide have been discussed in relation with meteorological factors and the mean values have been compared to those published in recent literature from other sites located at different latitudes. The annual average flux of (210)Pb and (7)Be were 47 and 700 Bq m(-2) y(-1), respectively. Observed seasonal variations of deposition data are explained in terms of different environmental features. The atmospheric deposition fluxes of (7)Be and (210)Pb were moderately well correlated with precipitation and well correlated with one another. The (210)Pb/(7)Be ratios in the monthly depositions samples varied in the range of 0.05-0.10 and showed a strong correlation with the number of rainy days.

Niveles de radionúclidos naturales y metales pesados en suelos urbanos de la ciudad de Cienfuegos, Cuba / Heavy metal and natural radionuclide levels in urban soils from Cienfuegos city, Cuba

Se determinan las concentraciones de metales pesados y radionúclidos naturales en suelos superficiales (0-10 cm) de la ciudad de Cienfuegos, Cuba, mediante las técnicas de fluorescencia de rayos X y espectrometría gamma respectivamente. Los resultados de la medición de metales pesados mostraron que las concentraciones promedio de Ni, Cu, Zn y Pb en los suelos estudiados son superiores a los valores correspondientes de fondo. El cálculo del Índice de Polución Integral permitió determinar que estos suelos presentan una contaminación severa por metales pesados. Las concentraciones de , y en los suelos urbanos de Cienfuegos se encuentran en los intervalos de 8.3-32.7, 3.7-10.7 y 129-356 , con promedios de 22.6, 6.3 y 272 respectivamente, valores que son similares a los reportados para la zona Centro-Sur de Cuba. La tasa de dosis absorbida en aire y la dosis equivalente efectiva anual que recibe la población local producto de la radiación natural es inferior a los límites establecidos internacionalmente. Se determinaron correlaciones positivas significativas de -Cu y -Zn, indicando la posible presencia de una fuente de contaminación por estos elementos en la zona.

Concentrations of heavy metals and natural radionuclides in topsoil (0-10cm) from Cienfuegos city, Cuba, were determined by using X-ray fluorescence analysis and gamma ray spectrometry, respectively. The measured results of heavy metals show that the mean concentrations of Ni, Cu, Zn and Pb in the studied soil samples are higher than their corresponding background values. The calculated results of integrated pollution index of heavy metals indicate that the studied soils present severely heavy metal contamination. The concentrations of , and in the studied soil samples range from 8.3 to 32.7, 3.7 to 10.7 and 129 to 356 with an average of 22.6, 6.3 and 272 , respectively, which are similar than the average concentrations reported for South-central Cuban soils. The air absorbed dose rate and the annual effective dose equivalent received by the local residents due to the natural radionuclides in soil are lesser than the worldwide established limits. A significantly positive -Cu and -Zn correlations were determined, indicating the possible existence of a source of pollution due to the presence of these elements in the area.

Observations of fallout from the Fukushima reactor accident in Cienfuegos, Cuba.

Following the recent accident at the Fukushima Daiichi nuclear power plant in Japan, radioactive contamination was observed near the reactor site. As a contribution towards the understanding of the worldwide impact of the accident, we collected fallout samples in Cienfuegos, Cuba, and examined them for the presence of above normal amounts of radioactivity. Gamma ray spectra measured from these samples showed clear evidence of fission products (131)I and (137)Cs. However, the fallout levels measured for these isotopes (135 ± 4.78 mBq m(-2) day(-1) for (131)I and 10.7 ± 0.38 mBq m(-2) day(-1)for (137)Cs) were very low and posed no health risk to the public. The doses received as consequence to the Fukushima fallout by the Cienfuegos population's (0.002 mSv per year) don't overcome the limit of dose (1 mSv per year) fixed for the public in Cuba.

Validación de un método para medir niveles de plutonio en sedimentos marinos en Cuba / Validation of a method to measure plutonium levels in marine sediments in Cuba

RESUMEN El principal objetivo de esta investigación fue desarrollar y validar un método de separación radioquímica del plutonio, factible desde el punto de vista económico y práctico en las condiciones de Cuba que nos permitiera determinar los niveles de plutonio en los sedimentos marinos de la bahía de Cienfuegos. El método de separación radioquímica seleccionado fue el de cromatografía aniónica y la técnica de medición, la espectrometría de masa con cuadrupolo y plasma inducido asociado. El método se aplicó a una muestra de referencia certificada, realizándose seis repeticiones y obteniéndose una buena correspondencia entre el valor medio medido de plutonio y su valor medio certificado. Se comprobó la buena reproducibilidad del método, ya que se obtuvo un coeficiente de variación de 11% para 95% de probabilidad. Los resultados de la aplicación del método validado, revelan que la presencia de plutonio en las muestras analizadas se debe únicamente a las precipitaciones radiactivas globales.

ABSTRACT The main objective of this research was to develop and to validate a method of radiochemical separation of plutonium, suitable from the economic and practical point of view, in Cuba conditions. This method allowed us to determine plutonium activity levels in the marine sediments from Cienfuegos Bay. The selected method of radiochemical separation was that of anionic chromatography and the measure technique was the quadrupole inductively coupled plasma mass spectrometry. The method was applied to a certified reference material, six repetitions were carried out and a good correspondence between the average measured value and the average certified value of plutonium was achieved, so the trueness of the method was demonstrated. It was also proven the precision of the method, since it was obtained a variation coefficient of 11% at 95% confidence level. The obtained results show that the presence of plutonium in the analyzed marine sediment samples is only due to the global radioactive fallout.