F. Garcias

Radium determination in mineral waters

Abstract We have determined the Radium concentration in several samples of natural mineral waters. Using a small volume of sample (≈ 100 ml), Ra isotopes are preconcentrated by adsorption onto a MnO2-impregnated cotton-filter, leached from the column with a hydroxylamine-HCl mixture and coprecipitated with BaSO4. 226Ra concentration has been determined using a low-background proportional counter and also from α-spectrometry. The results obtained show that the Radium concentration is around LLD for mineral surface waters, whereas thermal waters have activities exceeding the EPA limit for Ra in water.

Self-consistent extended Thomas-Fermi calculations in nuclei

Abstract We have solved the Euler-Lagrange (EL) equations corresponding to the ħ 4 -order extended Thomas-Fermi model for external potentials and nuclear forces of Skyrme type. We analyze in detail the ħ 2 - and ħ 4 -order contributions of the non-local terms arising from the nucleon effective mass and the spin-orbit force. Our results are compared with others obtained using different semiclassical methods. Some useful approximations to the exact ħ 4 EL equations are proposed in the case of general Skyrme forces.

Vertically coupled quantum dots in the local spin-density functional theory

We have investigated the structure of double quantum dots vertically coupled at zero magnetic field within local-spin-density functional theory. The dots are identical and have a finite width, and the whole system is axially symmetric. We first discuss the effect of thickness on the addition spectrum of one single dot. Next we describe the structure of coupled dots as a function of the interdot distance for different electron numbers. Addition spectra, Hund’s rule, and molecular-type configurations are discussed. It is shown that self-interaction corrections to the density-functional results do not play a very important role in the calculated addition spectra.

Ground-state properties of doped 3He clusters

In the framework of finite-range density functional (FRDF) theory, we have investigated the ground-state properties of 3HeN drops doped with inert gas atoms and SF6 molecules. Compared with the 4HeN case, the solvation energies turn out to be smaller, but still negative. Due to the attraction exerted by the impurity on the surrounding 3He atoms, doped drops of any size are bound. The number of 3He atoms in the first solvation shell is calculated, and it is compared with that of doped 4HeN drops, for which FRDF results are also available.

Determination of 137Cs and 90Sr in calcareous soils: Geographical distribution on the island of Majorca

Abstract In this work radioactive concentrations of the man-made radionuclides 137Cs, 89Sr and 90Sr have been studied in calcareous soils of the island of Majorca (Spain), by analysing the top 5 cm of the surface layer. The activity of 137Cs was determined by γ-ray spectrometry and ranged from about 10 to 60 Bq/kg. The possibility of carrying out extraction of Sr from calcereous soils was evaluated by using three different methods previously used in other samples with a high calcium content. Only the method based on precipitation in a fuming HNO3 medium gave rise to successful results with a yield of around 75%. The activity 90Sr was determined using a low-background αβ proportional counter. Results varied between about 2 and 8 Bq/kg. The activity of 89Sr was below the lower limit of detection.

Implementation of a Sequential Injection Pre-Treatment Method for Simultaneous Radium and Strontium Determination

A semi-automatic procedure for the simultaneous determination of Ra and Sr in two steps has been developed. In the first step, separation and pre-concentration of both analytes is performed by using a sequential injection procedure. In the second step, the activities of 226Ra and 90Sr, alpha and beta emitters, respectively, are determined using a low background proportional counter at the corresponding plateau potentials. 226Ra concentration is obtained by a single measurement of the precipitate. 90Sr activity is determined by means of its daughter 90Y carrying out two different measurements along the first day after the separation process; the solution of the Bateman radioactivity decay equations allows to obtain the initial 90Sr-90Y activities. The activities analysed in the present work have been ranged between 0-14 Bq/L for 226Ra and 0-175 Bq/L for 90Sr.

Rapid 90Sr/90Y determination in water samples using a sequential injection method

Abstract We have developed a semiautomatic procedure based on a sequential injection method for 90 Sr / 90 Y determination that allows their radiochemical separation in about 30 min. The method has been tested using 90 Sr / 90 Y solutions with activities lower than 12 Bq. The source is eluted in a pH = 6.5 medium through a MnO2-impregnated cotton filter, where 90 Y is preconcentrated in preference by adsorption. 90 Y is extracted from the column with hydroxylamine, some 90 Sr in the leached solution has also been found. After the radiochemical separation, the total β-activity of the leached solution has been determined using a low background α–β proportional counter and, assuming the presence of 90 Sr and 90 Y at t = 0, the solution of the Bateman equations allows the initial concentration of both isotopes to be obtained. We have verified that the addition of some ions usually found in water samples (Cl−, HCO3−, NO3−, SO42−, Ca2+, Mg2+) does not interfere with the yield of the radiochemical process, (90 ± 10)%. The method has been applied to 90 Sr / 90 Y determination in mineral waters, and even in thermal waters, where the salt concentration can be about 3500 mg/l, the radiochemical yield remains greater than 80%.

Development of an MSFIA-MPFS pre-treatment method for radium determination in water samples.

A new automatic method for preconcentration and separation of radium in water samples has been developed. Such method combines both multisyringe (MSFIA) and multi-pumping (MPFS) flow analysis techniques allowing to analyze larger sample volumes with a higher throughput than other previous methodologies. Ra adsorbed on MnO(2), deposited on cotton fiber, is eluted with hydroxylamine and subsequently coprecipitated with BaSO(4). (226)Ra activity is determined off-line by using a low background proportional counter. The procedure yield is (90+/-3)% and its lower limit of detection 0.05BqL(-1). This method has been applied satisfactorily to different types of spiked water (tap, mineral and seawater).

Thomas-Fermi calculations of the level density parameter of deformed nuclei☆

Abstract Constrained Thomas-Fermi calculations have been carried out for axially symmetric nuclear shapes in order to obtain the nuclear level density parameter a . For four selected nuclei and two different kinetic energy densities, we have calculated a as function of the quadrupole moment up to the saddle point value. The effect of rotation on a is also discussed.

The fission of hot rotating nuclei: A selfconsistent thomas-febmi calculation☆

Abstract We have studied the symmetric fission of excited nuclei within an axially deformed Thomas-Fermi model that incorporates selfconsistently the effect of rotation and temperature. We have used a realistic Skyrme force and included up to h 2 correction terms in the kinetic energy density.