3D scanning electron microscopy applied to surface characterization of fluorosed dental enamel.

The enamel surfaces of fluorotic teeth were studied by scanning electron stereomicroscopy. Different whitening treatments were applied to 25 pieces to remove stains caused by fluorosis and their surfaces were characterized by stereomicroscopy in order to obtain functional and amplitude parameters. The topographic features resulting for each treatment were determined through these parameters. The results obtained show that the 3D reconstruction achieved from the SEM stereo pairs is a valuable potential alternative for the surface characterization of this kind of samples.

Energy deposition of H and He ion beams in hydroxyapatite films: a study with implications for ion-beam cancer therapy.

Ion-beam cancer therapy is a promising technique to treat deep-seated tumors; however, for an accurate treatment planning, the energy deposition by the ions must be well known both in soft and hard human tissues. Although the energy loss of ions in water and other organic and biological materials is fairly well known, scarce information is available for the hard tissues (i.e., bone), for which the current stopping power information relies on the application of simple additivity rules to atomic data. Especially, more knowledge is needed for the main constituent of human bone, calcium hydroxyapatite (HAp), which constitutes 58% of its mass composition. In this work the energy loss of H and He ion beams in HAp films has been obtained experimentally. The experiments have been performed using the Rutherford backscattering technique in an energy range of 450-2000 keV for H and 400-5000 keV for He ions. These measurements are used as a benchmark for theoretical calculations (stopping power and mean excitation energy) based on the dielectric formalism together with the MELF-GOS (Mermin energy loss function-generalized oscillator strength) method to describe the electronic excitation spectrum of HAp. The stopping power calculations are in good agreement with the experiments. Even though these experimental data are obtained for low projectile energies compared with the ones used in hadron therapy, they validate the mean excitation energy obtained theoretically, which is the fundamental quantity to accurately assess energy deposition and depth-dose curves of ion beams at clinically relevant high energies. The effect of the mean excitation energy choice on the depth-dose profile is discussed on the basis of detailed simulations. Finally, implications of the present work on the energy loss of charged particles in human cortical bone are remarked.

Nuclear quadrupole resonance: a technique to control hydration processes in the pharmaceutical industry.

Pharmaceuticals can exist in many solid forms, which can have different physical and chemical properties. These solid forms include polymorphs, solvates, amorphous, and hydrates. Particularly, hydration process can be quite common since pharmaceutical solids can be in contact with water during manufacturing process and can also be exposed to water during storage. In the present work, it is proved that NQR technique is capable of detecting different hydrated forms not only in the pure raw material but also in the final product (tablets), being in this way a useful technique for quality control. This technique was also used to study the dehydration process from pentahydrate to trihydrate.

Effects of the carbon coating and the surface oxide layer in electron probe microanalysis.

Effects related with the attenuation and deflection suffered by an electron beam when it passes through a carbon conductive coating and an oxide film layer on the surface of bulk samples are studied by Monte Carlo simulations and energy dispersive spectroscopy with electron excitation. Analytical expressions are provided for the primary beam energy and intensity losses and for the deflection of the incident electrons in both layers, in terms of the incidence energy, the film mass thicknesses, and the atomic number of the oxidized element. From these analytical expressions, suitable corrections are proposed for the models used to describe the X-ray spectrum of the substrate, including also the contribution of the X-rays generated in the oxide and conductive films and the characteristic X-ray absorption occurring in those layers. The corrections are implemented in a software program for spectral analysis based on a routine of parameter refinement, and their influence is studied separately in experimental spectra of single-element standards measured at different excitation energies. Estimates for the layer thicknesses are also obtained from the spectral fitting procedure.