PENELOPE, A MONTE CARLO TOOL FOR QUANTITATIVE ELECTRON PROBE MICROANALYSIS F. Salvat 1 , X. Llovet 2 , J.M. Fern´ andez-Varea 1 1 Facultat de F´ ısica (ECM), Universitat de Barcelona. Diagonal 647. 08028 Barcelona. Spain. 2 Serveis Cient´ ıfico-T` ecnics, Univ. Barcelona. Llu´ ıs Sol´ e i Sabar´ ıs, 1-3. 08028 Barcelona. Spain. PENELOPE (an acronym for PENetration and Energy LOss of Positrons and Electrons) is a general-purpose Monte Carlo tool for the simulation of coupled electron-photon transport in material systems consisting of homogeneous bodies of arbitrary composition [1]. The code cov- ers a wide energy range, from 1 GeV down to ∼100 eV and incorporates routines for automatic tracking of particles in quadric geometries and for variance reduction techniques. The complete code system is publicly available from the OECD Nuclear Energy Agency and from the Radi- ation Shielding Information Computational Center. In this communication we shall focus on the capabilities of the most recent version of PENELOPE (2003) for quantitative electron probe microanalysis, using either the “default” physics models (included in the public version of the code) or more accurate interaction models developed for low-energy applications. PENELOPE allows the easy simulation of x-ray spectra emitted from homogeneous samples. The code has been validated by comparing simulated x-ray spectra with absolute spectra mea- sured on an electron microprobe, for elements covering the whole periodic system [2]. In general, the agreement between simulation and experiment is very good; the slight discrepancies found are usually attributable to detection artifacts and to inaccuracies in the available data on atomic relaxation. An advantage of using a general-purpose simulation tool with a robust geometry package is that it can be employed for studying specimens with complex geometrical structures. Thus, PENELOPE has been used to study multilayered structures, grain boundary effects, particulate samples, as well as porous media and rough surfaces. The physical interaction models implemented in PENELOPE, and in any other general-purpose code, are necessarily approximate. Thus, for example, the photoelectric cross sections pertain to free atoms and, therefore, possible extended x-ray absorption fine structure effects are dis- regarded. Similarly, the x-ray energies and transition probabilities of inner-shell vacancies are those of free atoms and, consequently, the effect of aggregation on these quantities is neglected. Also the cross sections for certain interaction mechanisms are approximated by means of ana- lytical approximations, which not only allow a reduction in the volume of numerical information needed but also permit the use of numerically robust sampling methods. Nevertheless, the struc- ture of the code has been kept flexible enough to allow the use of alternative, more elaborate physical models when needed. The accuracy of simulated x-ray spectra is mostly determined by the adopted cross sections for bremsstrahlung emission and inner-shell ionization by electron impact, together with the elec- tron transport model (scattering and slowing down). PENELOPE simulates bremsstrahlung events by using the most accurate differential cross sections (DCS) available, expressed as the Microsc Microanal 9(Suppl 2), 2003 Copyright 2003 Microscopy Society of America DOI: 10.1017/S1431927603442670 534 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1431927603442670 Downloaded from https://www.cambridge.org/core. IP address: 23.94.80.80, on 07 May 2019 at 16:33:26, subject to the Cambridge Core terms of use, available at