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- Author or Editor: P. Rosales x
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Abstract
The determination of thirteen elements, eleven rare-earth elements (La, Ce, Nd, Sm, Eu, Gd, Tb, Ho, Tm, Tb and Lu), thorium and uranium were performed by instrumental neutron activation analysis for four geological reference materials (G-2, AGV-1, GSP-1 and SY-2) as well as our laboratory rare-earth standard. The analyses were performed using a low energy photon detector coupled to an Apple IIe microprocessor employed as a multichannel analyzer not only to collect the data but also for data analysis. Finally, based on this work we have proposed a simple, rapid routine method for the determination of eleven rare-earth elements, thorium and uranium in geological materials employing IVIC's RV-1 nuclear reactor.
Abstract
The concentration of137Cs, potassium, thorium and uranium for 6 monitoring sites and 32 other sites at the Venezuelan Institute for Scientific Research (IVIC) were presented, as well as, the estimated air dose and exposure rates for each site. The concentration of137Cs was found to be much higher at many sites at IVIC in respect to the average estimated value of137Cs in Venezuela. But, this was determined to be due to a natural cause, the cloud forest which surrounds the higher elevations. The values of potassium, thorium and uranium were compared to values from other parts of northern Venezuela and were found to agree for sites at similar elevations. They were also shown to be about two to three times higher than global estimates. Thus, the air dose and exposure rates were correspondingly two to three times higher too, but the annual dose from the primordial radionuclides in the soil was estimated to be less than 0.1 mSv, which is considered negligible for health risks.
Abstract
The activity of137Cs was determined in mosses and their surrounding soils in three Venezuelan cloud forests. The concentration of137Cs in both the mosses and their respective soils were correlated with elevation (m.a.s.l.). This relationship was the result of the cloud forest effect, no direct deposition by condensation below the base of the clouds and increasing deposition of137Cs with the density of the clouds. The ratio of the activity of137Cs in the mosses to their surrounding soils was in general the same for sites near the top of the mountains, but the ratio at the Altos de pipe location was 3.5 times higher than that of the La Sierra mountain. This was explained by the difference in the water content of the surface and the top soil layer. It was concluded that the137Cs measured in the mosses was from the soil effect rather than new deposition of137Cs in the last three years.
Abstract
Two sets of calibration standards for134Cs and137Cs were prepared by small serial dilution of a natural matrix standard reference material, IAEA-154 whey powder. The first set was intended to screen imported milk powders which were suspected to be contaminated with134Cs and137Cs. Therefore the concentration range of the calibration standards were about 40–400 Bq/kg. The precision of the preparation of the standard with about 7 Bq/kg of134Cs and 39 Bq/kg of137Cs at measurement time was 7.4% and 3.2%, respectively. The preparation of a similar standard by spiking the matrix with radioisotope solutions resulted in a poorer precision, about double that of the former technique. The other set of calibration standards was prepared to measure the environmental levels of137Cs in commercial Venezuelan milk powders. Their concentration ranged from 3–10 Bq/kg of137Cs. The accuracy of these calibration curves was checked by using IAEA-152 and A-14 milk powders. Their measured values were in good agreement with their certified values. Finally, it is shown that these preparation techniques by serial dilution of a standard reference material were simple, rapid, precise, accurate and cost-effective.
Abstract
The activity of 137 Cs in surface soils (2-5 cm) was determined at twenty-one sampling sites along the northwestern and eastern coast of the Paraguana peninsula (Venezuela), as well as, at nine locations, between 95 and 535 m.a.s.l. on Cerro Santa Ana. The measurements were performed by high-resolution gamma-ray spectroscopy employing a compatible IBM computer. Most of the values were much higher than those found along the coastline of the mainland; four sites were found to be anomalously high, with 137 Cs values greater than 10 Bq/kg. It is difficult to explain these anomalous 137 Cs values by geographical or climatological factors since there is little rainfall here and the clouds and fog are rarely if never present along the coast of the peninsula. Possibly, some mechanism of the mist that is blown ashore could explain these anomalies. The values of the 137 Cs versus altitude on the Cerro Santa Ana show an increase of two or three times at 500 m.a.s.l. level, thus we have concluded that the base of the clouds was at this height when the fallout was directly deposited by condensation in this cloud forest. These results in the Cerro Santa Ana cloud forest are similar to those of other cloud forests along the Venezuelan coast, but the altitude (m.a.s.l.) of the base of the clouds here are much lower.
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.
Abstract
Soils were collected at different elevations (m.a.s.l.) near the two roadways, that pass through the Henri Pittier National Park (Edo. Aragua, Venezuela) in order to determine the distribution of the concentrations of the 137Cs fallout and its relation to the tropical cloud forest. Duplicate samples were taken at most elevations between 2–5 cm below the soil surface to confirm that the samples were representative of the area. In many cases, it was difficult or impossible to locate areas that were undisturbed by man or nature. The 137Cs (Bq/kg) content was determined by conventional high resolution gamma ray spectroscopy employing a standard comparison method. The background of the 137Cs fallout in soils, below the cloud (fog) baseline was calculated to be about 5 Bq/kg on both the south (land) side and north (ocean) side for both roadways. The concentrations of 137Cs (Bq/kg) were between 2–3 times higher at the baseline of the cloud (fog) on both sides of the mountain range. The 137Cs values at the highest elevations (1105 and 1625 m.a.s.l.) near the roadways were about 5–6 times higher than the determined background levels. Our estimates of the baseline of the cloud (fog) are in good agreement with other visual observations. Finally, we have concluded that the distribution of 137Cs in soils in cloud forests can be employed to estimate the baseline and the concentrations of 137Cs fallout can be related to the relative density of the cloud (fog) when it was deposited.
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.
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.
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.
