Monte Carlo Calculation of the Energy Spectrum of a 6 MeV Electron Beam using PENetration and Energy Loss of Positrons and Electrons Code.

BACKGROUND: The limited bibliographic existence of research works on the use of Monte Carlo simulation to determine the energy spectra of electron beams compared to the information available regarding photon beams is a scientific task that should be resolved. AIMS: In this work, Monte Carlo simulation was performed through the PENELOPE code of the Sinergy Elekta accelerator head to obtain the spectrum of a 6 MeV electron beam and its characteristic dosimetric parameters. MATERIALS AND METHODS: The central-axis energy spectrum and the percentage depth dose curve of a 6 MeV electron beam of an Elekta Synergy linear accelerator were obtained by using Monte Carlo PENELOPE code v2014. For this, the linear accelerator head geometry, electron applicators, and water phantom were simplified. Subsequently, the interaction process between the electron beam and head components was simulated in a time of 86.4x104 s. RESULTS: From this simulation, the energy spectrum at the linear accelerator exit window and the surface of the phantom was obtained, as well as the associated percentage depth dose curves. The validation of the Monte Carlo simulation was performed by comparing the simulated and the measured percentage depth dose curves via the gamma index criterion. Measured percentage depth- dose was determined by using a Markus electron ionization chamber, type T23343. Characteristic parameters of the beam related with the PDD curves such as the maximum dose depth (R100), 90% dose depth (R90), 90% dose depth or therapeutic range (R85), half dose depth (R50), practical range (Rp), maximum range (Rmax), surface dose (Ds), normalized dose gradient (G0) and photon contamination dose (Dx) were determined. Parameters related with the energy spectrum, namely, the most probable energy of electrons at the surface (Ep,0) and electron average energy (E- 0) were also determined. CONCLUSION: It was demonstrated that PENELOPE is an attractive and accurate tool for the obtaining of dosimetric parameters of a medical linear accelerator since it can reliably reproduce important clinical data such as the energy spectrum, depth dose, and dose profile.

Microscopy and microanalysis of complex nanosized strengthening precipitates in new generation commercial Al-Cu-Li alloys.

Precipitates (ppts) in new generation aluminum-lithium alloys (AA2099 and AA2199) were characterised using scanning and transmission electron microscopy and atom probe tomography. Results obtained on the following ppts are reported: Guinier-Preston zones, T1 (Al2 CuLi), ß' (Al3 Zr) and δ' (Al3 Li). The focus was placed on their composition and the presence of minor elements. X-ray energy-dispersive spectrometry in the electron microscopes and mass spectrometry in the atom probe microscope showed that T1 ppts were enriched in zinc (Zn) and magnesium up to about 1.9 and 3.5 at.%, respectively. A concentration of 2.5 at.% Zn in the δ' ppts was also measured. Unlike Li and copper, Zn in the T1 ppts could not be detected using electron energy-loss spectroscopy in the transmission electron microscope because of its too low concentration and the small sizes of these ppts. Indeed, Monte Carlo simulations of EEL spectra for the Zn L2,3 edge showed that the signal-to-noise ratio was not high enough and that the detection limit was at least 2.5 at.%, depending on the probe current. Also, the simulation of X-ray spectra confirmed that the detection limit was exceeded for the Zn Kα X-ray line because the signal-to-noise ratio was high enough in that case, which is in agreement with our observations.