Dans le cadre du projet européen CONRAD (COordinated Network for RAdiation Dosimetry,contrat FP6-12684) coordonné par EURADOS (EUropean RAdiation DOSimetry group), le groupede travail numéro 4 avait pour objectif de s’intéresser à la dosimétrie numérique avec uneaction particulière appelée “Uncertainty assessment in computational dosimetry : anintercomparison of approaches”. Le principe de cette action était de proposer à lacommunauté internationale huit exercices de modélisation traitant de domaines variésconcernant le transport du rayonnement (photons, neutrons, protons et électrons). Le butde cet article est de présenter l’exercice n4˚ traitant de la simulation d’un faisceau de137Cs pour le calcul du kerma dans l’air. Il avait pour objectif principald’estimer l’incertitude sur la valeur du kerma dans l’air en prenant en compte descomposantes de celle-ci non accessibles à la mesure, notamment celles dues aux différentsparamètres de la géométrie : position de la source, diamètre du collimateur, densité desmatériaux, etc. 12 instituts de 10 pays différents ont participé à cet exercice montrantl’intérêt de cette proposition.

The scanning helium ion microscope has been used in transmission mode to investigate both the feasibility of this approach and the utility of the signal content and the image information available. Operating at 40 keV the penetration of the ion beam, and the imaging resolution achieved, in MgO crystals was found to be in good agreement with values predicted by Monte Carlo modeling. The bright-field and annular dark-field signals displayed the anticipated contrasts associated with beam absorption and scattering. In addition, the diffraction of the He ion beam within the sample gave rise to crystallographic contrast effects in the form of thickness fringes and dislocation images. Scanning transmission He ion microscopy thus achieves useful sample penetration and provides nanometer scale resolution, high contrast images of crystalline materials and crystal defects even at modest beam energies.

The International Technology Roadmap for Semiconductors ranks dopant profiling as one of the most difficult challenges for analysis of semiconductors. Dopant mapping in the scanning electron microscope (SEM) has the potential to provide a solution. This technique has not yet found widespread application, however, mainly due to the lack of a comprehensive theoretical model, uncertain quantification, and its inability to differentiate doping levels in n-type silicon. Although a Monte Carlo model was recently published that closely matched experimental data obtained in p-doped silicon to data obtained from the theoretical model, a large discrepancy between experimental data obtained for n-type silicon was found. Here we present a Monte Carlo model that provides close matches between experimental and calculated data in both n- and p-type silicon, paving the way for a widespread application of SEM dopant contrast.