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  • Author or Editor: J. LaBrecque x
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Abstract  

A new technique was applied for exciting X-rays for X-ray fluorescence analysis by “direct” beta excitation for the determination of noble metals in catalytic materials.

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Abstract  

In this work we shall discuss the preliminary results of employing eleven different radionuclides for elemental X-ray analysis using a new analytical technique. This new technique mixes the radioisotope directly with the sample and this source sample is directly placed on the detector window which is protected by a thin plastic film from contamination. An equal atomic mixture of eight elements (Ti, Mn, Zn, Br, Zr, Ag, Sn and Ag) was prepared and doped separately with the eleven different isotopes (Pm-147, S-35, Ni-63, Na-22, Co-137, Co-57, Cd-109, I-125, Am-241, Zn-65 and Fe-55). The spectrum of each is shown herein with a discussion of the background, signal to noise ratio, corrected peak intensities, etc. Finally, the possible future applications of this technique with some of the isotopes are presented.

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Abstract  

An improved method for the determination of ruthenium in catalytic materials based on a relative fluorescence ratio factor is presented. This method employs a thin-film technique and an internal standard technique to minimize absorption and enchancement effects. The samples and standards were fluorescent with a109Cd (7 mCi) annular source for 200 seconds and the data were collected and analyzed with an Apple II+ micro computer. Precision (total variation) for typical ruthenium catalysts in the range of 1–5% ruthenium was about 2%. Finally, the concentration of ruthenium in six commercial catalysts was determined for both alumina and carbon supports.

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Abstract  

Measurements of radon in potable mineral waters along the Cota Mil Highway at two sites, La Castellana with five sampling points within 20 meters of each other and two collection points at the San Jose site were carried out from November, 1997 to December, 1998. Temporal radon variation patterns will be presented for the seven sampling points, which had very different water flow rates and short-term variations. The extraction of the radon from mineral waters was accomplished in the laboratory a few hours after sampling and the measurements were performed employing a radiation monitor with a scintillation cell 18 hours latter to insure that the radon and its decay products were in equilibrium. The results suggest that the increase of radon from the middle of February to the middle of November can be related to the decrease in atmospheric temperature and rainfall. The large differences in the minimum and maximum values of radon and the short-term variations show the need for many measurements over a year to quantify a correct annual value to be employed in dose calculation for radiological impact studies on human health. Finally, we have also concluded that water sampling points with very low water flow rates are more suitable for investigating the possible relation between radon anomalies and seismic events.

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Abstract  

A rapid radiochemical separation of selenium from arsenic, germanium and zinc based on the precipitation of elemental selenium by NaHSO3 is discussed. Yields of 90% and greater are achieved for selenium in 1 to 2 min. The kinetics, separation characteristics of the process and chemical yield of Se and trace contaminants such as Zn, Ge and As were studied using nondispersive X-ray fluorescence techniques.

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Abstract  

The optimum sample size and arrangement for flat-disc samples employing a commercial annular241Am radioactive source and a planar pure germanium detector were studied for quantitative X-ray fluorescence analysis. The effective overall sample areas at different heights (distances between the source and sample) were estimated simply by drawing to scale the source-sample-detector arrangement and its accessories. The effective sample areas were also determined experimentally with standard samples and aluminium shields. The rough estimate was in good agreement with the experimental values for the effective overall areas. Finally, data concerning the shift of the centroid of the Am-scatter peak due to the 59.6 keV gamma-rays from 48.7 to 52.0 keV, with its respective resolution for the different heights, are discussed with respect to the characteristic rare-earth element X-rays in this energy region.

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Abstract  

Clam meats were obtained directly from the fishermen on the beaches in front of where the clams were collected at eight sites; seven along the northern coast of Venezuela and one on the northern coast of the island of Margarita (Venezuela). Marine sediments were also collected in the same corresponding areas as the clams. 137Cs was determined both in clam meats and the marine sediments by high resolution gamma-ray spectrometry employing a hyperpure germanium detector. About 5 kg portions of clam meats were washed and dried in the laboratory, before 500 cm3 volumes were transferred and weighed in the measuring containers. Similarly, 500 cm3 volumes of marine sediments that were dried and ground to pass a 85 μm sieve were transferred to the measuring containers. The samples were counted for 150,000 seconds of real time. The 137Cs activity of the clam meats ranged from <0.011 Bq·kg−1 (our detection limit) to 0.36 Bq·kg−1 (dried weigh). These values are all within the range of values considered for environmental fallout from the nuclear weapons tests. Finally, all the values for the corresponding marine sediments were below our detection limit of 0.1 Bq·kg−1 of 137Cs (dried weigh).

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Summary  

Radon measurements were performed across two sections of the Avila fault near Caracas, Venezuela. The radon concentrations clearly showed the different tectonic features and lithology at the Tacamahaca and Spanish Trail sites. 214Bi (U-cps) measurements also were related to the lithology. The passive radon method employed laboratory-made dosimeters with LR 115, type 2 celulose nitrate films as detectors. They were buried in the ground at 30 cm depth. While, the active radon method was performed with a Pylon radon measurement system with Lucas cells. The soil gas was also sampled at 30 cm depths, but for only one minute, which was sufficient to fill the 150 cm3 Lucas cells completely. The total radon counts were then separated into those corresponding to 222Rn (radon) and 220Rn (thoron) by a simple computer routine. A comparison of the active and passive methods for the Tacamahaca section over a three-month period showed that both methods could locate precisely the active fault trace.

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Abstract  

The comparison of an ambient temperature mercuric iodide spectrometer (HgI2) with a conventional cooled Si(Li) spectrometer is presented for the determination of niobium in Venezuelan laterites in the laboratory. The energy resolution of the HgI2 spectrometer was only about 590 eV (FWHM) at 5.9 keV compared to about 150 eV for the conventional Si(Li) spectrometer. The efficiency was about 5 times lower in the region of the NbK peak as compared to the Si(Li) detector. Even though its energy resolution and efficiency is much poorer than the conventional Si(Li), the results it produced for the determination of niobium were acceptable for use in the exploration and exploitation of a niobium-rich deposit such as Cerro Impacto, Estado Bolívar, Venezuela.

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Abstract  

A simple and rapid technique is presented to determine the relative counts of 214Bi in surface soils to locate active fault traces of the El Pilar Fault in the state of Sucre, Venezuela. The method employes a portable differential gamma-ray spectrometer on site with 300 seconds of measuring time. Three transects across the El Pilar fault of very different geological aspects were studied. One of the advantages of this technique in respect to determining 222Rn in soil-gas is that no soil-gas probes are required to be inserted in the soil and it is not necessary to know the appropriate depth. Finally, it has been suggested that measurements of 1000 seconds would be preferred rather than 300 seconds for future studies even though this would limit the number of measurements to about 20 per day.

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