G.B. Baptista

Methodology and application of the nuclear resonance reaction 16O(α, α)16O for the profiling of titanium oxide

Abstract A method is presented for the application of the 16 O(α,α) 16 O resonance at 3.045 MeV to the depth profiling of oxide films. The resonance yield is translated into oxygen to metal stoichiometry as a function of the depth probed. The method is applied to anodic titanium oxide films grown in the absence and presence of tungsten anions. The oxygen depth profile is then utilized to obtain the profile of the dopants (W) incorporated in the oxide. A depth resolution of 6 μg/cm is achieved. The incorporation of tungsten anions of the order of 2 at.%, evaluated from the RBS yields, precludes the establishment of a constant oxygen to metal stoichiometry in the doped film. The tungsten atomic fractions have an estimated error of 5%.

Analysis of trace elements in human hair by PIXE

Abstract The PIXE method was applied to the analysis of trace elements in scalp hair using two methods for target preparation. In the first method eight hair strands each of nearly circular cross-section and having approximately the same diameter were selected and placed on an aluminum frame. In the second method a given mass of hair was dissolved in nitric acid and a known amount of strontium was added to the solution and dripped onto a membrane filter using a micropipette. The results for the concentrations of trace elements in hair obtained by the two methods are compared and several aspects of the analysis are discussed.

Analysis of the composition of surface layers in high‐temperature superconducting materials by the combination of Rutherford backscattering spectrometry and nuclear resonance reaction

Rutherford backscattering spectrometry combined to the 16O(α, α) nuclear resonance (E=3.045 MeV) are used to determine the stoichiometry of Y‐Ba‐Cu‐O superconducting samples. The oxygen depth profile is also measured at thin surface layers of the compound.

PIXE analysis of elemental concentrations in human hair and nails

Abstract The PIXE technique was applied to examine the elemental concentrations in scalp hair and nails collected over several months from three subjects living in Rio de Janeiro, Brazil. The results were then compared with data taken from the literature, and with the range and average elemental concentrations obtained by analyzing, using the same technique and laboratory conditions, samples of scalp hair taken from 51 men and 50 women living in another region of Latin America.

Study of a proton beam diffusing system for pixe analysis

Abstract The experimental arrangement for uniformization and profile determination of the proton beam from the Van de Graaff accelerator at PUC/RJ is described and a discussion about the effects of the diffuser thickness and relative positron to the target on the beam uniformity is presented.

The K-shell excitation function in the plane-wave Born approximation: transitions to the continuum and discrete (H atom) states

An exact analytical expression for the energy differential K-shell ionisation cross section is obtained in the framework of the plane-wave Born approximation (PWBA). The excitation function I( eta , theta ) is expressed in terms of elementary analytical functions plus a rapidly convergent power -series expansion. With a few terms of the power series the values obtained by numerical integration are reproduced within the precision inherent in the available tables. Starting from the same general formulation an exact algebraic equation for the 1s-n excitation for atomic hydrogen is also obtained.

Uncertainties in elemental quantitative analysis by PIXE

Abstract The effects of the degree of non-uniformity of the particle beam, matrix composition and matrix thickness in a quantitative elemental analysis by particle induced X-ray emission (PIXE) are discussed and a criterion to evaluate the resulting degree of uncertainty in the mass determination by this method is established.

Coincidence counting analysis of secondary ions emitted from a phenylalanine target under multicharged MeV carbon bombardment

Abstract Coincidence counting techniques for time-of-flight mass spectrometry have been applied to the study of secondary ion correlations. Phenylalanine samples were exposed to 2.5 MeV carbon ions with charge states ranging from +1 to +6. The influences of the projectile charge state on secondary ion yields and correlations are reported. The degree of secondary ion correlation was observed to decrease as the charge state of the primary ion increases. For the cases studied, the data indicate that more inefficient projectiles are better suited for monitoring secondary ion correlations.

Size distribution of airborne particulates in monazite dust

Abstract A six-stage cascade impactor was used to collect airborne dust particulates in the grinding area of a monazite separation plant. The samples were analysed using particle-induced X-ray emission (PIXE) to determine the elemental concentrations, with special attention to thorium and uranium concentrations. The particle size distribution of the samples containing thorium and uranium were determined. The mass median aerodynamic diameter (MMAD) obtained was 1.15 μm for both elements. The activity median aerodynamic diameter (AMAD) was estimated based on the MMAD. The results are compared with ICRP recommendations for derived air concentrations (DAC) for thorium and uranium in restricted areas.

X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry study of anion incorporation in anodically grown films

Abstract Anodic oxide films on titanium and zirconium were grown in the presence of sodium tungstate. The surface and bulk characteristics of these films have been analyzed by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) as a function of terminal voltage and temperature. XPS results show a close association between the sodium and tungsten incorporated from the forming solution at the film surface. The RBS data reveal the existence of the tungsten species in a layered structure. These layers are distributed at regularly spaced intervals beneath the surface. The results are discussed in terms of a periodic precipitation reaction, also known as the Liesegang phenomenon.