M.P. Rubio Montero

Radioactivity in bottled mineral waters.

Consumption of bottled mineral water is a growing practice and is sometimes a necessity rather than a choice. In this work, a study of the radioactive content of a wide selection of commercial bottled mineral waters for human intake was carried out. The origins of the analyzed waters were very different, coming from various locations in France, Portugal and Spain. Their total alpha and beta activity concentrations were determined and also gamma spectrometry was used to detect some radionuclides. In some cases, the waters presented high values of the total alpha and beta activity concentrations surpassing the reference levels established by the CSN, the Spanish. Regulatory Organization. In these cases, a determination of uranium and 226Ra was also performed by using low-level liquid scintillation counting. The results revealed a strong correlation between radioactive content and dry residue, and lead one to conclude that high radioactive content is mainly related to the mineralization in waters of underground origin.

Isotopic uranium and plutonium analysis by alpha-particle spectrometry

An isotopic uranium analysis of environmental and man-made samples was performed by alpha-particle spectrometry. A fitting technique using blocks of peaks in the spectra measured with silicon detectors was developed. Samples of natural uranium from conventional mines and from the Bangombe natural nuclear reactor were analysed. The isotope composition of depleted and enriched uranium samples was also determined. The technique was applied to determining the isotope composition of plutonium samples, identifying whether the samples were reactor-grade or weapons-grade plutonium. Spectra of soil samples from Palomares and others from an inter-laboratory comparison exercise were analysed, yielding very good results.

Analysis of plutonium in soil samples

Abstract Procedures for analysis of plutonium in soil samples were developed using anion exchange as a purification technique. Special attention was paid to removing impurities of 228 Th which interferes in 238 Pu determination by alpha spectrometry. Two anion-exchange methods were compared. The determination of plutonium in soil involves the conversion of soil samples to acid-soluble form. Two methods for the extraction of plutonium from a natural reference soil were compared. The first method (a direct digestion in nitric acid) is suitable for the determination of plutonium in large amounts of sample. The second method involves microwave digestion of soil (5 g) with a mixture of HNO3, HCl and HF, and is suitable for saving time in routine determinations. Activities calculated with a reference soil matrix were in good agreement with the reference value. The microwave digestion method was applied in a study of different soil samples, and recoveries ranged between 20% and 50%.

Study of inhomogeneities in sources prepared for α-particle spectrometry using scanning probe microscopy

Abstract For high-resolution α -particle spectrometry, sources of high quality must be prepared by methods giving the thinnest and most homogeneous deposit possible on a suitable support. Surface characteristics of several types of α -particle sources were studied using a scanning probe microscope. Major inhomogeneities were observed, which means that the materials and techniques used for the preparation of sources must be improved.

Radioactive content of charcoal

Coal and charcoal present similar physical and chemical characteristics. There is no standardized procedure to distinguish them. However, their differences in age and origin result in several differences in their natural radionuclide content. Moreover, charcoal can be contaminated with fallout. In this work, activity concentrations of (228)Th, (226)Ra, (40)K, and (137)Cs were determined in charcoal and coal samples in order to obtain evidence to distinguish the two kinds of sample.

The effect of energy losses in α-particle sources on the shape of peaks in spectra obtained with wide-angle geometry

Abstract It has been shown that two main effects contribute to the tailing in the shapes of α- peaks measured with silicon detectors: the ionization loss in the source and the response of the detector. We studied the relative influence of both factors in measurements with small source-to-detector distances. The computer simulation code ‘the stopping and range of ions in matter’ has been used to obtain the energy spectra of a 226 Ra source as a function of the source thickness. Results of the simulation are compared with experimental measurements.

Determination of alpha activity in solid samples by leaching or digestion

The analysis of solid environmental samples by α-particle spectrometry generally involves processes requiring an initial treatment to destroy the complexes in the matrix, and dissolve the radionuclides of interest. This study compared the activities obtained for several natural radionuclides ((238)U, (234)U, (230)Th, (226)Ra, and (210)Po) in previously well-characterized materials, using two procedures: acid leaching and digestion in a microwave oven. The measured activities were in general very similar for the two procedures, with a strong statistical correlation between the two sets of values.

Evaluation of two radiochemical procedures for the determination of uranium and thorium isotopes in coal samples

Two procedures are presented for the sequential determination of uranium and thorium isotopes in coals. They are based on acid leaching on a hot plate, and on acid digestion in closed vessels using microwave irradiation. Both were applied to the analysis of International Atomic Energy Agency (IAEA) and National Institute of Standards and Technology (NIST) reference materials, and to the study of coals with different ranks. The greatest recoveries were obtained with the acid digestion method. This method was more effective than the leaching method for the extraction of the uranium isotopes in coals. The effectiveness of the thorium isotopes extraction was similar in the two methods.

Measuring solar limb-darkening with modest equipment

In solar images the brightness of the Sun decreases from the centre of the disc toward the limb. This effect is called solar limb-darkening. In this work, measurements performed with very simple experimental equipment are presented and discussed, comparing the obtained values of the linear limb-darkening coefficient with results from theoretical solar atmosphere models included in the literature. This low-cost practical experience is highly appropriate for educational use in undergraduate laboratories.

Radioactive characterization of charcoal as a tool in identifying fossil contamination

In the pyrolysis process carried out to obtain charcoal from plants, a concentration of the radionuclides found in trace amounts in the raw material is produced. This fact would influence its possible uses. Radioactive characterization of a wide set of charcoal samples from different provenances was analysed. Activity concentrations of the radionuclides from the 238U and 232Th series, and also for 40K, 134Cs and 137Cs nuclides were obtained by gamma-ray and alpha-particle spectrometry. A discussion of these results is included comparing them with coal. A possible contamination of charcoal samples by fossil matter, such as coal, was studied via 14C analysis carried out by accelerator mass spectrometry.