Structure of the icosahedral Ti-Zr-Ni quasicrystal

The atomic structure of the icosahedral Ti-Zr-Ni quasicrystal is determined by invoking similarities to periodic crystalline phases, diffraction data and the results from ab initio calculations. The structure is modeled by decorations of the canonical cell tiling geometry. The initial decoration model is based on the structure of the Frank-Kasper phase W-TiZrNi, the 1/1 approximant structure of the quasicrystal. The decoration model is optimized using a new method of structural analysis combining a least-squares refinement of diffraction data with results from ab initio calculations. The resulting structural model of icosahedral Ti-Zr-Ni is interpreted as a simple decoration rule and structural details are discussed.Comment: 12 pages, 8 figure

E18-2007-91 SIMULATIONS OF PROTON BEAM DEPTH-DOSE DISTRIBUTIONS

Rajcan M., Molokanov A. G., Mumot M. E18-2007-91 Simulations of Proton Beam Depth-Dose Distributions Proton beams are successfully used in radiotherapy. A correct modiˇcation of beam parameters enables to spare normal surrounding tissues from radiation action. Our work is focused on passive beam-shaping techniques, which are used to modify the proton beam properties. The beam passes through the scattering system, which consists of scattering materials, energy degraders, drift spaces and collimators. In order to model the proton beam transport through the scattering system, the new Monte Carlo (MC) computer code Track has been developed. The code Track can predict output proton beam parameters modulated by various system adjustments and helps to optimize them. It calculates a beam proˇle, creates beam emittance diagram at a speciˇed position of the system and predicts proton beam depthdose distribution in a water phantom. In addition it calculates beam losses on individual components. We present a physical model of the beam transport calculations and algorithm implemented in a code Track. We compared the Track code calculations of depth-dose distributions in water phantom with experimental data and with a set of MC calculations in the FLUKA code. The accuracy of simulation results and calculation time in Track code are observed