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  • Author or Editor: J. LaBrecque x
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Abstract  

In this study, we have investigated the fluctuations of radon levels in two experimental rooms constructed for secondary standard dosimetric calibration. The values over the short-term (the first two weeks) were in the range of 10–14 pCi/L of radon in air, while those of the long-term were between 6–14 pCi/L of radon. Even though the temperature and humidity was relatively constant during the second half of the rainy season, there was a trend towards lower radon values. It is concluded that ventilation is an important factor in indoor radon levels.

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Abstract  

A rapid procedure for determining palladium in catalysts and geoiogical materials is presented. This method involves the use of an241Am (100 mC) source for excitation and employs a PDP-11/05 processor for the data acquisition and analysis by energy-dispersive X-ray fluorescence. The relative standard deviation for 5 independent determinations is less than 3% for 100 seconds of fluorescent time. The calculated and measured values agreed well for both, the prepared standards and the doped Venezuelan laterites. Finally, data on the different sources of error is given including counting time, sample preparation, and total error.

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Abstract  

The determination of soil-gas anomalies especially 222Rn anomalies, are important to precisely locate fault traces, as well as to investigate earthquake precursors. In this paper, we have studied and compared new rapid methods for on site determinations of radon (222Rn), thoron (220Rn) and total radon (222Rn+220Rn) in soil-gas. These new techniques pump the soil-gas continuously from the soil through a simple sampling tube to the counting cell for one-minute with discarding the excess. Then, either four one-minute counting periods (5-minute technique) or nine one-minute counting intervals (10-minute technique) are followed immediately. In all the methods, conversely to Morse"s method, the first counting period (C1) was not employed for calculations. Three calculation methods for the five-minute technique, two for the ten-minute technique and a modified Morse"s method are compared with theoretical values and different real soil-gases with different radon/thoron ratios. The affect of different flow rates of soil-gases into the counting cell was also investigated. Finally, the ten-minute technique seems to be a little more accurate, but the 5-minute technique is much more suitable for seismic field studies when a much larger number of determinations are required in a short time.

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Abstract  

A rapid, non-destructive method is presented for the determination molybdenum and cobalt in hydrodesulfurization catalysts employing a PDP-11/05 computer-base radioisotope x-ray fluorescence technique. Precision for molybdenum and cobalt better than 2.5% and 4.0%, respectively, are achieved in 100 sec of fluorescent time. The values obtained by this method are in agreement with values from atomic absorption and neutron activation methods. Besides being nondestructive, only about 50 mg of sample is needed, and no time-consuming acid dissolution is required as in atomic absorption and colorimetric methods. The results for six different commercial catalysts are compared with determinations by atomic absorption, neutron activation analysis methods as well as an x-ray fluorescence system with manual calculations of the percentage of molybdenum and cobalt.

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Abstract  

More than one hundred undisturbed soil samples from Northern Venezuela and the islands of Margarita and Los Roques have been analyzed for137Cs,40K,238U and232Th by -ray spectroscopy. The specimens were taken from between 5–10 cm below the earth's surface. Thus, they are valid not only for the137Cs deposition studies but also for the estimation of the natural -ray dose from primordial radionuclides that form the terrestrial component. The concentration of40K was directly determined from its 1461 keV -ray, while those of137Cs,238U and232Th were performed using a -ray from one of their daughter radionuclides: the 661 keV -ray of137mBa for137Cs, the 1760 keV -ray of214Bi for238U and the 2620 keV -ray of208Tl for232Th. Finally, the concentration values were compared with those of global estimates.

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Abstract  

Fault traces have been previously located from measurements of 222Rn in soils taken a constant soil-depth across the fault trace. In this paper, we have studied the uranium-series disequilibria of the 226Ra, 222Rn (gas) and 214Bi radionuclides, not only for their horizontal spatial patterns across the fault trace, but also for their vertical spatial patterns near and at the fault trace itself. Radon-222 activities in the soil-gas were measured on-site with a radiation monitor and a Lucas cell. Radium-226 and 214Bi were determined in soil samples in the laboratory by gamma-ray spectroscopy. A new technique employing the measurement of 222Rn versus soil-depth shows a decrease in 222Rn activity at the fault trace due to the much higher soil-gas permeability as a result of the fractured soil, as well as relative larger uranium-series disequilibria, in respect to an increase in 222Rn activity at normal sites, where the soil is not fractured. Finally, it is suggested that fault trace detection could possibly also be performed by measuring 214Bi in surface soils (0-100 cm) along a transect.

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Abstract  

The activity of cesium-137 (Bq/kg) in surface soils between 2-5 cm was determined for more than ninety sample sites on the Araya Peninsula, the Paria Peninsula and the isthmus in between them in the state of Sucre (Venezuela). The measurements were performed by high-resolution gamma-ray spectroscopy, employing a compatible IBM computer with a Nucleus analog to digital interface card. In general, the values for the 137Cs activities were much greater on the Paria Peninsula than the Araya Peninsula and slightly lower on the isthmus. Even though the peninsulas are only separated by a small isthmus, their environmental characteristics are very different. The large difference in the annual rainfall of the peninsulas could have resulted in a greater amount of deposition of 137Cs on the Paria Peninsula, as well as other environmental characteristics, such as altitude and vegetation. The difference of the environmental characteristics could also affect the degree of disturbances of the soils by natural processes on the peninsulas and the isthmus, which could also have affected the 137Cs activity distribution. Finally, an anomalous high 137Cs activity distribution was found at the farthest southeastern sample sites and one of lesser extent at the most northern sample sites. These anomalies are possibly due the direct affect of the northeasterly winds which transported the 137Cs fallout from the nuclear weapon test sites.

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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.

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Abstract  

More than fifty surface (2-10 cm) soil samples were collected in the Gran Sabana and Sierra de Pacarima, State of Bolivar (Venezuela) and analyzed for their 137Cs activity. The measurements were performed by high resolution gamma-ray spectrometry employing a hyperpure germanium detector with an energy resolution of about 1.8 keV for the 1.33 MeV line of 60Co and a counting efficiency greater than 25%. About 500 ml portions of dried soil samples with less than 85 mm particle size were counted for 20,000 seconds and the data were collected, stored and analyzed with an IBM-compatible computer. The concentrations of 137Cs in most samples were below the detection limit of 1.2 Bq/kg, but many of these soil samples could have been disturbed not only by man but the nature itself, for example, by the large amount of rainfall in the wet season. Only 15% of the soil samples were determined to have values equal or greater than 2 Bq/kg and only two of these were greater than 10 Bq/kg. The study area was divided into five zones, which had different environmental characteristics: climate, annual average rainfall, temperature ranges, elevations (m.a.s.l.), soil types and vegetation. Finally, it was concluded that the high 137Cs activities could be associated with the areas of higher annual rainfall and with very humid pre-mountainous climate rather than with humid tropical climate.

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Abstract  

The activity of 137Cs was determined in soils, mosses, lichens and other vegetation along the Caruay River and near the town of Kavanayen. The range of values for the soils was from <1.2 Bq·kg−1 of 137Cs (our detection limit) to 14.1 Bq·kg−1. The range of 137Cs activities in the mosses ranged from 9.9 to 17.9 Bq·kg−1 with a mean value of 13.4±4 Bq·kg−1; all the moss samples were found along the river. While the 137Cs activities in the lichens ranged from 9.1 to 29.8 Bq·kg−1; the two values along the river were about three factors higher than the one near Kavanayen. It was concluded that the 137Cs activities in the soils, mosses and lichens are much higher along the river in respect to the nearby town of Kavanayen.

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