Biomedical subjects

F Vera Tomé

Publications and source records attributed to F Vera Tomé.

10 recordsLinked to original sources

PubMed2005

Linearity assumption in soil-to-plant transfer factors of natural uranium and radium in Helianthus annuus L.

The linearity assumption of the validation of soil-to-plant transfer factors of natural uranium and (226)Ra was tested using Helianthus annuus L. (sunflower) grown in a hydroponic medium. Transfer of natural uranium and (226)Ra was tested in both the aerial fraction of plants and in the overall seedlings (roots and shoots). The results show that the linearity assumption can be considered valid in the hydroponic growth of sunflowers for the radionuclides studied. The ability of sunflowers to translocate uranium and (226)Ra was also investigated, as well as the feasibility of using sunflower plants to remove uranium and radium from contaminated water, and by extension, their potential for phytoextraction. In this sense, the removal percentages obtained for natural uranium and (226)Ra were 24% and 42%, respectively. Practically all the uranium is accumulated in the roots. However, 86% of the (226)Ra activity concentration in roots was translocated to the aerial part.

Biodegradation, Environmental↗

PubMed2005

Fractionation of natural radionuclides in soils from a uranium mineralized area in the south-west of Spain.

A new version of a classical method was applied to study the distribution of natural radionuclides (238U, 230Th, and 226Ra) in the soil fractions obtained by a sequential extraction procedure. The potential significance of the fractions obtained with this method was tested on two very similar soils but with very different contents of the three radionuclides, collected in the proximity of a disused uranium mine located in the Extremadura region in the south-west of Spain. The results confirmed that, if only non-residual fractions are considered, the sequential method applied shows a characteristic speciation pattern of these natural radionuclides in this soil matrix, i.e., the distribution of each of the three radionuclides was very similar for the two soil samples.

Environmental Monitoring↗

PubMed2004

A simple method for 210Pb determination in geological samples by liquid scintillation counting.

A simple procedure for the determination of 210Pb in geological samples using liquid scintillation counting is presented. Following the acid digestion of the sample, the method uses sulphate precipitation for the radiochemical separation. Finally, lead oxalate is precipitated, and once re-dissolved, it is mixed with ULTIMA GOLD AB scintillator cocktail. The measurement is performed using a low-level LKB Quantulus 1220 spectrometer and the two-window technique. Calibration studies were performed to evaluate the interference of 210Bi in the 210Pb measurement. The method was tested on a geological reference sample, and gave satisfactory results and high reproducibility.

Bismuth↗

PubMed2002

Distribution of long-lived radionuclides of the 238U series in the sediments of a small river in a uranium mineralized region of Spain.

A study is presented on the distribution and mobilization of the natural U isotopes (238U and 234U), 230Th, and 226Ra in the sediments of a small river crossing an uranium mineralized zone where a disused uranium mine is located. Due to the preferential directions for surface run-off waters and to the mine's situation, one sampling point along the river bed was identified as a point of accumulation of radionuclides. The average values of the activity concentrations (Bq/kg) in this sediment sample were 5,025, 5,055, 5,915 and 1,694 for 238U, 234U, 230Th and 226Ra, respectively, while the respective average values of the activity concentrations (Bq/kg) for the sediment sample considered to give the background level were 125, 124, 131 and 370. Isotopic ratios between the descendants of 238U served to clarify some paths of distribution, involving the soils nearest to the sampling points and the location of these points with respect to the disused mine. The differences in behaviour found between the uranium, thorium and radium isotopes were associated to the mobility of these radionuclides in the fluvial system studied. Correlations between the radionuclide activity concentration ratios and stable element concentrations in the sediment samples were also investigated.

Fresh Water↗

PubMed2002

On the use of 225Ra as yield tracer and Ba(Ra)SO4 microprecipitation in 226Ra determination by alpha-spectrometry.

A simple procedure for the determination of 226Ra in geological samples using alpha-spectrometry is presented. The method uses 225Ra as yield tracer, and microprecipitation of Ba(Ra)SO(4) for source preparation. Extensive studies were performed in order to determine the chemical yield of the proposed procedure with precision. The method was tested on a geological reference sample, and gave satisfactory results and high reproducibility.

Journal Article↗

PubMed2001

Concerning the low uranium and thorium yields in the electrodeposition process of soil and sediment analyses.

The very low yields obtained in a common method of alpha-particle spectrometry for the determination of uranium and thorium in soil and sediment samples of environmental origin were investigated. Several experiments were performed to determine the cause. The results suggest that aluminium may cause major chemical interference in the electrodeposition process, and can be considered to be primarily responsible for the low recoveries found. A procedure is proposed to resolve this problem.

Alpha Particles↗

PubMed2000

Sequential method for the determination of uranium, thorium and 226Ra by liquid scintillation alpha spectrometry.

A new procedure for the determination of uranium, thorium and 226Ra from the same aliquot of an aqueous sample using extractant scintillators and liquid scintillation alpha spectrometry is proposed. The procedure is designed such that the same aqueous phase can be used in all the stages, with slight modifications. The procedure is thus very simple, requiring little manipulation of the sample. Testing of the procedure was performed obtaining satisfactory results and high reproducibility.

Environmental Monitoring↗

PubMed1999

Procedures for the determination of 222Rn exhalation and effective 226Ra activity in soil samples.

Two methods for measuring 222Rn exhalation and effective 226Ra in soil samples were studied. In the first determination, the method employed was based on the adsorption of radon onto activated charcoal and subsequent measurement of the activity of its daughters with an HPGe (high-purity germanium) detector. In the second, vials containing an aqueous suspension of the sample, mixed with an insoluble high efficiency mineral oil scintillation cocktail, were measured using a low-level liquid scintillation counter. Studies of optimum sampling time, efficiency in both procedures, variation of 226Ra efficiency with quenching, as well as the effect of sample amount and granulometry upon the quenching parameter, were carried out. The two methods were applied to the determination of 222Rn exhalation and effective 226Ra in environmental samples.

Charcoal↗

PubMed1998

Extractive procedure for uranium determination in water samples by liquid scintillation counting.

An extractive procedure for uranium determination using liquid scintillation counting with the URAEX cocktail is described. Interference from radon and a strong influence of nitrate ion were detected in this procedure. Interference from radium, thorium and polonium emissions were very low when optimal operating conditions were reached. Quenching effects were considered and the minimum detectable activity was evaluated for different sample volumes. Isotopic analysis of samples can be performed using the proposed method. Comparisons with the results obtained with the general procedure used in alpha spectrometry with passivated implanted planar silicon detectors showed good agreement. The proposed procedure is thus suitable for uranium determination in water samples and can be considered as an alternative to the laborious conventional chemical preparations needed for alpha spectrometry methods using semiconductor detectors.

Nitrates↗

PubMedDate not supplied

Sequential extraction for radionuclide fractionation in soil samples: a comparative study.

Two sequential extraction procedures, Tessier's method (Anal. Chem. 51(7) (1979) 844), and a current version known as Schultz's method (J. Environ. Radioact. 40(2) (1998) 155), were compared. The two procedures were applied to a natural soil sample that presents high activity concentrations in natural radionuclides of the 238U series. Reproducibility studies of each method and a comparison between the two sets of results were performed for uranium, thorium, and radium. The results were different for each radionuclide. Analysis of the extracted fractions was carried out by alpha spectrometry.

Alpha Particles↗