Electron probe microanalysis (EPMA) is based on the comparison of characteristic intensities induced by monoenergetic electrons. When the electron beam ionizes inner atomic shells and these ionizations cause the emission of characteristic X-rays, secondary fluorescence can occur, originating from ionizations induced by X-ray photons produced by the primary electron interactions. As detectors are unable to distinguish the origin of these characteristic X-rays, Monte Carlo simulation of radiation transport becomes a determinant tool in the study of this fluorescence enhancement. In this work, characteristic secondary fluorescence enhancement in EPMA has been studied by using the splitting routines offered by PENELOPE 2008 as a variance reduction alternative. This approach is controlled by a single parameter NSPLIT, which represents the desired number of X-ray photon replicas. The dependence of the uncertainties associated with secondary intensities on NSPLIT was studied as a function of the accelerating voltage and the sample composition in a simple binary alloy in which this effect becomes relevant. The achieved efficiencies for the simulated secondary intensities bear a remarkable improvement when increasing the NSPLIT parameter; although in most cases an NSPLIT value of 100 is sufficient, some less likely enhancements may require stronger splitting in order to increase the efficiency associated with the simulation of secondary intensities.

Fluorescence enhancement in samples irradiated in a scanning electron microscope or an electron microprobe should be appropriately assessed in order not to distort quantitative analyses. Several models have been proposed to take into account this effect and current quantification routines are based on them, many of which have been developed under the assumption that bremsstrahlung fluorescence correction is negligible when compared to characteristic enhancement; however, no concluding arguments have been provided in order to support this assumption. As detectors are unable to discriminate primary from secondary characteristic X-rays, Monte Carlo simulation of radiation transport becomes a determinant tool in the study of this fluorescence enhancement. In this work, bremsstrahlung fluorescence enhancement in electron probe microanalysis has been studied by using the interaction forcing routine offered by penelope 2008 as a variance reduction alternative. The developed software allowed us to show that bremsstrahlung and characteristic fluorescence corrections are in fact comparable in the studied cases. As an extra result, the interaction forcing approach appears as a most efficient method, not only in the computation of the continuum enhancement but also for the assessment of the characteristic fluorescence correction.

In electron probe microanalysis, secondary fluorescence can occur leading to an increase of the volume analysed, degrading the lateral resolution of this technique. An adequate knowledge of the interaction volumes from where the different signals of interest are detected is determinant to estimate the minimum size of the zone that can be characterized. In this work, the size of the signal source volume is surveyed for a wide set of samples at different beam energies. To this aim, the PENELOPE software package was chosen to run Monte Carlo simulations for several experimental situations in order to produce the various lateral radiation distributions of interest. A comparison between the interaction volumes of the different signals was performed by taking into account the different fluorescence enhancement possibilities. An unexpected behaviour was found in the particular cases of aluminium and alumina, where the secondary photons signal exhibits a decreasing trend up to certain beam energy (∼17 keV); this implies that lower beam energies may degrade the lateral resolution of the technique in these materials.

Fast neutron detection is a subject of great relevance in modern nuclear science and engineering, in particular, with the recent advances in nuclear fusion research, detection of fast neutron became a key issue. Nuclear properties of carbon are of special interest due to its relatively high capture cross section for fast neutrons. Devices made of silicon carbide and diamond are based on these properties, and so are being developed to be used with the proper wiring. In addition, in recent years carbon nano-tubes unveiled their electrical and mechanical properties, which can be exploited for neutron detection. In this work, we use MCNP5 Monte Carlo code to analyze the carbon nuclear properties and discuss the way nano-tubes can be used for fast neutron detection.