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  • Author or Editor: J. LaBrecque x
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Abstract  

A rapid radioisotope induced energy-dispersive X-ray fluorescence procedure for the simultaneous determinations of Cobalt, Nickel and Molybdenum in hydrodesulfurization catalysts is presented. A109Cd (7 mCi) source is used as the excitation system coupled to a high resolution Si(Li) detector. A PDP-11/05 processor is employed as a multichannel analyzer and also to automatically control the complete system by means of a prewritten computer program. The relative standard deviations for the three determinations (CoO, NiO and MoO3) are less than 5% for 300 seconds of fluorescent time for a typical sample. Finally a comparison of results by different methods is given to check the accuracy since no standard reference materials are available for catalytic material.

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Abstract  

Immediately, after the July 9, 1997 earthquake (Ms = 6.8) in the state of Sucre, Venezuela, we began measuring radon in water to investigate the possible correlations with the seismic activity and to study the meteorological affects. Sampling periods were for 3–5 days with 4–8 weeks in between each. During the first two sampling periods, the seismic activity was high with several minor events (Mb4.0) and anomalous radon concentrations were measured and considered as possible precursors for the events. We have also shown that the radon activity was stable except for daily meteorological effects during periods of low seismic activity. The radon activity during the first year after the major event on July 9, 1997, at the beginning of the rainy season increased from about 50 pCi/l to about 350 pCi/l for all sampling points. Then abruptly dropped to 100 pci/l at the beginning of the next rainy season for points #1 and #2 in the Casanay river and stayed relativelystable during the second year. At the start of the third year, the values began to increase again, similarly to the first year. We concluded that this was caused by the heavy rainfall at the beginning of the rainy season. While at the sampling points at Hotel Cristal, thermal spring pool, it decreased slowly during the second year but increased again at the onset of the third year. Finally, we have concluded as other investigators, that monitoring radon activity alone is insufficient to predict minor earthquakes (Mb4.0), but in some cases it can be considered as a precursor.

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Abstract  

This work presents the results of 137Cs, 40K, 232Th and 238U concentration (Bq kg−1) values in coastal marine sediments collected from 38 sites along the coastline of the island of Margarita, Venezuela. The purpose was to determine baseline values for these radionuclides in surface marine sediments and to detect if there were any anomalously high concentration values. Only three of the 38 sediments analyzed had measurable values above the detection limit of 0.9 Bq kg−1 for 137Cs and the highest only being 1.4 Bq kg−1. While, the concentration (Bq kg−1) ranges for the primordial radionuclides, 40K, 232Th and 238U were as follows: 12.2–211.7, <1.5–9.8 and <4.4–20.7, respectively. These concentration ranges for the primordial radionuclides can be considered as baseline values for surface marine sediments for areas that are considered not polluted by man or contaminated by nature. Finally, the concentration range of 137Cs can also be employed as baseline values, which only seem to have been the result of the atmospheric testing of nuclear weapons in the past.

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Abstract  

The concentrations of40K,226Ra,232Th and137Cs were determined in the upper layers of soils in the central coastal region of Venezuela. The activities of137Cs are higher in the areas where the forest is well developed, oriented towards the wind and at higher elevations. The origin of the137Cs deposition is from water input from the clouds directly in the cloudforest and rainfall from the northeast trade winds. Even though the values of137Cs are much higher in these areas, there is little or no significant increase in the health risk. The natural radioactivity is correlated with the geology in the region except in the area of Urama. The values for the natural radiation background are as follows: for potassium between 1–3%, for radium between 1–3 ppm and for thorium the range was 6–39 ppm. The corresponding amounts of absorbed dose rates in air, the exposure rates and the annual effective dose equivalents are in the following ranges respectively: 11–39 pGy/s, 4–16 uR/h and 0.25–0.86 mSv/y. The annual effective dose equivalents include the contribution of the global average (2.57 mSv/y) of the rest of the natural sources of radiation. Finally, the largest natural radioactivity background, was found near Chichiriviche as a result of the massive granite deposits in this area, but again there is no significant health risk.

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