Browsing by Author "Ahmed, A"

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    Comparative study of alternative Geant4 hadronic ion inelastic physics models for prediction of positron-emitting radionuclide production in carbon and oxygen ion therapy
    (IOP Publishing, 2019-08-01) Chacon, A; Guatelli, S; Rutherford, H; Bolst, D; Mohammadi, A; Ahmed, A; Nitta, M; Nishikido, F; Iwao, Y; Tashima, H; Yoshida, E; Akamatsu, G; Takyu, S; Kitagawa, A; Hofmann, T; Pinto, M; Franklin, DR; Parodi, K; Yamaya, T; Rosenfeld, AB; Safavi-Naeini, M
    The distribution of fragmentation products predicted by Monte Carlo simulations of heavy ion therapy depend on the hadronic physics model chosen in the simulation. This work aims to evaluate three alternative hadronic inelastic fragmentation physics options available in the Geant4 Monte Carlo radiation physics simulation framework to determine which model most accurately predicts the production of positron-emitting fragmentation products observable using in-beam PET imaging. Fragment distributions obtained with the BIC, QMD, and INCL + + physics models in Geant4 version 10.2.p03 are compared to experimental data obtained at the HIMAC heavy-ion treatment facility at NIRS in Chiba, Japan. For both simulations and experiments, monoenergetic beams are applied to three different block phantoms composed of gelatin, poly(methyl methacrylate) and polyethylene. The yields of the positron-emitting nuclei 11C, 10C and 15O obtained from simulations conducted with each model are compared to the experimental yields estimated by fitting a multi-exponential radioactive decay model to dynamic PET images using the normalised mean square error metric in the entrance, build up/Bragg peak and tail regions. Significant differences in positron-emitting fragment yield are observed among the three physics models with the best overall fit to experimental 12C and 16O beam measurements obtained with the BIC physics model. © 2019 Commonwealth of Australia, Australian Nuclear Science and Technology Organisation, ANSTO.
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    Synthesis, tensile testing, and microstructural characterization of nanometric SiC particulate-reinforced Al 7075 matrix composites
    (Springer, 2010-06) Ahmed, A; Neely, AJ; Shankar, K
    This article examines the reasons for the poor performance of the nanometric scale SiC (n-SiC p) particulate-reinforced Al 7075 composites. The composites having different volume fractions of the n-SiC p were synthesized via powder metallurgy (P/M) route and were uniaxially tested at room temperature. Experimental results showed a significant drop in the hardness and tensile properties of the composites in comparison with those of the monolithic Al. Microstructural analysis via scanning electron microscopy (SEM) revealed large segregation of Mg in the vicinity of the n-SiC p and at the grain boundaries of the Al matrix, which plausibly changed both the aging kinetics and tensile behavior of the Al matrix. The segregation of Mg increased with an increase in the volume fraction of the n-SiC p in the Al matrix. No Mg segregation was found in the monolithic Al. The clustering of the n-SiC p was observed from SEM with energy dispersive X-ray analysis. SEM also revealed cracks in the n-SiC p clusters and debonding between the clusters and Al matrix, which were considered as the main mode of fracture in the composites. © 2010, Springer. The original publication is available at © Springer Nature