PENELOPE-2005. A Monte Carlo Code System Suitable for Simulation of X-ray Spectra

Abstract

Monte Carlo (MC) simulation of x-ray spectra emitted from targets bombarded by electron beams is of interest in x-ray microanalysis, especially for the quantitative interpretation of measurements under unconventional conditions. Examples are the analysis of non-homogeneous samples (at the micron scale) such as particulate matter, multilayer films or samples with rough surfaces, the analysis at grazing-angle incidence or at very-low incident electron energies. The usefulness of MC simulation stems from its ability to incorporate realistic interaction models devoted to describing the evolution of electrons in the sample and to track not only primary electrons but also all secondary radiations (electrons and photons) generated within the sample.penelope is a general-purpose MC code that allows the simulation of coupled electron-photon transport in targets consisting of bodies with arbitrary composition, for an energy range from 100 eV to 1 GeV [1]. The interaction models implemented in the code are based on the most reliable information available at present, limited only by the required generality of the code. These models combine results from first-principles calculations, semi-empirical models and evaluated data bases. penelope is coded as a set of FORTRAN subroutines that perform the random sampling of interactions and the tracking of electrons and photons. Hence, the user must provide a main program so as to follow the particle tracks through the target and keep score of the quantities of interest.The latest public version of penelope was released in 2003 and it is available from the OECD Nuclear Energy Agency Data Bank (http://www.nea.fr). We are now preparing a new version 2005 of the code that contains substantial improvements in the interaction models and in the geometry routines, which will be released in a few months. Namely, it incorporates numerical differential cross sections for elastic scattering obtained from partial-wave analysis using DiracFock atomic electron densities and the exchange potential of Furness and McCarthy. These cross sections were obtained by using the code elsepa [2]. Another improvement is that it allows the simulation of characteristic x rays and Auger electrons that result from vacancies produced in M-shells. The structure of the code is still flexible enough to enable the use of alternative, more elaborate interaction models when available. For instance, the cross sections for ionization of inner shells (by electron impact) implemented by default, which were evaluated using the method of virtual quanta, are reliable only for electrons with kinetic energies well above the ionization threshold. In the present simulations we have replaced these cross sections by more accurate values calculated from the distorted-wave Born approximation [3].As in previous versions of penelope, the tracking of particles in the target can be done automatically with the aid of the subroutine package pengeom, provided the target is defined as a

Secondary Fluorescence Correction for Characteristic and Bremsstrahlung X-Rays Using Monte Carlo X-ray Depth Distributions Applied to Bulk and Multilayer Materials

“…As for the bremsstrahlung fluorescence contribution, although they all show the same trend, the values from MC X-ray increase compared with the other two. This is due to the difference in bremsstrahlung X-ray intensities resulting from the difference in bremsstrahlung generation cross-section models (Kirkpatrick & Wiedmann, 1945; Seltzer & Berger, 1985; Gauvin et al, 2006; Llovet & Salvat, 2006). DTSA-II and PENEPMA use the Seltzer and Berger model (Seltzer & Berger, 1985), while MC X-ray uses the Kirkpatrick and Wiedmann model (Kirkpatrick & Wiedmann, 1945).…”

“…Table 1 shows the time per simulation (seconds) and the average and standard deviation of the total intensity (primary intensity, characteristic fluorescence intensity, and bremsstrahlung fluorescence intensity). To facilitate the comparison of the three models, an efficiency-like value was also computed using the efficiency ε Q equation for a quantity Q , which is defined by Llovet & Salvat (2006), where is the average value of Q after N simulations, σ Q is the standard deviation of Q , and T is the average simulation time for a single simulation with units of seconds. The simulated electron number for all simulations was 1,000.…”

Experimental study on the Ag L-shell X-ray production cross-sections with thick-target method induced by positrons up to 9 keV

“…The detection efficiency calibration of the SDD was performed by using the same method described in ref. [8], i.e., the SDD was used to obtain the experimental bremsstrahlung spectrum of 19 keV electrons bombarding a high-purity thick carbon target (thickness of 2 mm), and the corresponding theoretical bremsstrahlung spectrum was calculated by the Monte Carlo PENELOPE-2005 code [21]. The relative efficiency calibration curve was determined from the ratio of the experimental to the theoretical bremsstrahlung spectra, and then it was normalized to the absolute detection efficiency curve through the absolute efficiency of a 241 Am standard radioactive source at 13.9 keV.…”

“…where E 0 is the incident positron energy; n γ (E 0 ) is the peak net counting rates at 511 keV recorded by the HPGe detector when the positrons with energy E 0 bombarded the thick target; ξ(E 0 ) is the number of annihilation photons detected by the HPGe detector when a positron with energy E 0 impacted on the thick target. Its value was determined by Monte Carlo simulation using the PENELOPE-2005 code [21]. The values of ξ(E 0 ) for Ag target in this work are shown in table 1; ε EXP is the HPGe detection efficiency for 511 keV γ photon, it was measured by using a 22 Na standard point source placed at the target position; ε MC is similar to ε EXP but calculated with the PENELOPE-2005 code [21].…”

“…Its value was determined by Monte Carlo simulation using the PENELOPE-2005 code [21]. The values of ξ(E 0 ) for Ag target in this work are shown in table 1; ε EXP is the HPGe detection efficiency for 511 keV γ photon, it was measured by using a 22 Na standard point source placed at the target position; ε MC is similar to ε EXP but calculated with the PENELOPE-2005 code [21].…”