Evaluation of ArcCHECK SNC Machine QA tool for Modern Linear Accelerator

Purpose: ArcCHECK SNC Machine QA tool is used to test geometric and delivery aspects of linear accelerator.Methods: In this study we evaluated the performance of this tool. For each item analyzed by the tool, wherever possible, tests across the same time period using portal dosimetry were also evaluated. Machine QA feature allows user to perform quality assurance tests using ArcCHECK phantom. Following tests can be performed 1) Gantry Speed, Rotation and Angle 2) MLC/Collimator 3) Beam Profile Flatness and Symmetry. Data was collected on true BEAM STx for a year. All plans were created for 6 and 10 MV beams as per the SNC patient user manual in Eclipse v.13.Results: The Gantry speed was 3.9 deg/sec with speed maximum deviation around 0.3 deg/sec. The Gantry Isocenter for arc delivery was 0.9 mm and static delivery was 0.4 mm which was well consistent with MPC (0.4 mm). The average maximum percent positive and negative diff was found to be 1.9%, -0.25% and average maximum distance positive and negative diff was 0.4 mm, -0.3 mm for MLC/Collimator QA. The average gamma error at 1% 1 mm criteria was 1.4% using portal Dosimetry for 6 MV. The Flatness for Arc delivery was 1.8% and Symmetry for Y was 0.8% and X was 1.8%.Conclusion: ArcCHECK SNC Machine QA tool is useful for quality assurance of modern linear accelerators as it tests both geometric and delivery aspects. This test can be incorporated in the regular quality assurance protocol for VMAT delivery

High-Temperature Phonon Spectra of Multiferroic BiFeO3 from Inelastic Neutron Spectroscopy

We report inelastic neutron scattering measurements of the phonon spectra in a pure powder sample of the multiferroic material BiFeO3. A high-temperature range was covered to unravel the changes in the phonon dynamics across the Neel (T_N ~ 650 K) and Curie (T_C ~ 1100 K) temperatures. Experimental results are accompanied by ab-initio lattice dynamical simulations of phonon density of states to enable microscopic interpretations of the observed data. The calculations reproduce well the observed vibrational features and provide the partial atomic vibrational components. Our results reveal clearly the signature of three different phase transitions both in the diffraction patterns and phonon spectra. The phonon modes are found to be most affected by the transition at the T_C. The spectroscopic evidence for the existence of a different structural modification just below the decomposition limit (T_D ~ 1240 K) is unambiguous indicating strong structural changes that may be related to oxygen vacancies and concomitant Fe3+ to Fe2+ reduction and spin transition

Experimental and theoretical investigations on the polymorphism and metastability of BiPO4

In this work we report the metastability and the energetics of the phase transitions of three different polymorphs of BiPO4, namely trigonal (Phase-I, space group P3(1)21), monoclinic monazite-type (Phase-II, space group P2(1)/n) and SbPO4-type monoclinic (Phase-III, space group P2(1)/m) from ambient and non-ambient temperature powder XRD and neutron diffraction studies as well as ab initio density functional theory (DFT) calculations. The symmetry ambiguity between P2(1) and P2(1)/m of the high temperature polymorph of BiPO4 has been resolved by a neutron diffraction study. The structure and vibrational properties of these polymorphs of the three polymorphs have also been reported in detail. Total energy calculations have been used to understand the experimentally observed metastable behavior of trigonal and monazite-type BiPO4. Interestingly, all of the three phases were found to coexist after heating a single phasic trigonal BiPO4 to 773 K. The irreversible nature of these phase transitions has been explained by the concepts of the interplay of the structural distortion, molar volume and total energy.This study was supported by the Spanish government MEC under grants no: MAT2010-21270-C04-01/04, by MALTA Consolider Ingenio 2010 project (CSD2007-00045), and by the Vicerrectorado de Investigacion y Desarrollo of the Universidad Politecnica de Valencia (UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11). S. N. A. acknowledges the support provided by Universitat de Valencia during his visit to it. A. M. and P. R.-H. acknowledge the computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster.Achary, SN.; Errandonea, D.; Muñoz, A.; Rodríguez Hernández, P.; Manjón Herrera, FJ.; Krishna, PSR.; Patwe, SJ.... (2013). Experimental and theoretical investigations on the polymorphism and metastability of BiPO4. Dalton Transactions. 42:14999-15015. https://doi.org/10.1039/c3dt51823jS14999150154

Experimental and theoretical investigations on structural and vibrational properties of melilite-type Sr2ZnGe2O7 at high pressure and delineation of a high pressure monoclinic phase

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.5b00937"We report a combined experimental and theoretical study of melilite-type germanate, Sr2ZnGe2O7, under compression. In situ high-pressure X-ray diffraction and Raman scattering measurements up to 22 GPa were complemented with first-principles theoretical calculations of structural and lattice dynamics properties. Our experiments show that the tetragonal structure of Sr2ZnGe2O7 at ambient conditions transforms reversibly to a monoclinic phase above 12.2 Gpa with similar to 1% volume drop at the phase transition pressure. Density functional calculations indicate the transition pressure at, similar to 13 GPa, which agrees well with the experimental value. The structure of the high-pressure monoclinic phase is closely related to the ambient pressure phase and results from a displacive-type phase transition. Equations of state of both tetragonal and monoclinic phases are reported. Both of the phases show anisotropic compressibility with a larger compressibility in the direction perpendicular to the [ZnGe2O7](2-) sheets than along the sheets. Raman-active phonons of both the tetragonal and monoclinic phases and their pressure dependences were also determined. Tentative assignments of the Raman modes of the tetragonal phase were discussed in the light of lattice dynamics calculations. A possible irreversible second phase transition to a highly disordered or amorphous state is detected in Raman scattering measurements above 21 GPa.Research supported by the Spanish government MINECO under Grant Nos. MAT and CSD2007-00045 and MAT2013-46649-C4-1/2/3-P. S.N.A. acknowledges the support provided by Universitat de Valencia during his visit there.Achary, SN.; Errandonea, D.; Santamaría-Pérez, D.; Gomis, O.; Patwe, SJ.; Manjón Herrera, FJ.; Rodríguez Hernández, P.... (2015). Experimental and theoretical investigations on structural and vibrational properties of melilite-type Sr2ZnGe2O7 at high pressure and delineation of a high pressure monoclinic phase. Inorganic Chemistry. 54(13):6594-6605. doi:10.1021/acs.inorgchem.5b00937S65946605541

High-pressure crystal structure, lattice vibrations, and band structure of BiSbO4

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.inorgchem.6b00503”The high-pressure crystal structure, lattice-vibrations HP crystal structure, lattice vibrations, and band , and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressure on it. They also predict a possible high-pressure phase. A room-temperature pressure volume equation of state is determined, and the effect of pressure on the coordination polyhedron of Bi and Sb is discussed. Raman- and infrared-active phonons were measured and calculated. In particular, calculations provide assignments for all the vibrational modes as well as their pressure dependence. In addition, the band structure and electronic density of states under pressure were also calculated. The calculations combined with the optical measurements allow us to conclude that BiSbO4 is an indirect-gap semiconductor, with an electronic band gap of 2.9(1) eV. Finally, the isothermal compressibility tensor for. BiSbO4 is given at 1.8 GPa. The experimental (theoretical) data revealed that the direction of maximum compressibility is in the (0 1 0) plane at similar to 33 degrees (38 degrees) to the c-axis and 47 degrees (42 degrees) to the a-axis. The reliability of the reported results is supported by the consistency between experiments and calculations.Research supported by the Spanish government MINECO under Grant Nos. MAT2013-46649-C4-1/2/3-P and MAT2015-71070-REDC. We also acknowledge the computer time provided by MALTA cluster and the Red Espanola de Supercomputacion. Experiments were performed at MSPD beamline at ALBA Synchrotron Light Facility with the collaboration of ALBA staff.Errandonea, D.; Muñoz, A.; Rodríguez-Hernández, P.; Gomis, O.; Achary, SN.; Popescu, C.; Patwe, SJ.... (2016). High-pressure crystal structure, lattice vibrations, and band structure of BiSbO4. Inorganic Chemistry. 55(10):4958-4969. doi:10.1021/acs.inorgchem.6b00503S49584969551

Crystal structure, electrical, and thermal properties of Ca<SUB>0.5</SUB>Th<SUB>0.5</SUB>VO<SUB>4</SUB>

Ca0.5Th0.5VO4 was prepared by a solid-state reaction of component oxides and characterized by powder x-ray diffraction (XRD) at ambient and higher temperatures and impedance spectroscopy. Crystal structure was refined by Rietveld refinements from powder XRD data. At room temperature, Ca0.5Th0.5VO4 has a zircon-type tetragonal (I41/amd) lattice with unit cell parameters: a = 7.2650(1) and c = 6.4460(1) Å. Despite the large charge difference, Ca2+ and Th4+ are statistically distributed over a single site. The crystal structure of Ca0.5Th0.5VO4 is built from the (Ca/Th)O8 (bisdisphenoid) and VO4 tetrahedra. The in situ high-temperature XRD studies on Ca0.5Th0.5VO4 revealed anisotropic thermal expansion behavior with coefficients of thermal expansion αc = 10.96 × 10−6/°C and αa = 5.32 × 10−6/°C. The impedance measurements carried out in the temperature range from ambient to 800 °C indicate semiconducting behavior with appreciable ionic conductivity above 400 °C. The activation energy obtained from the temperature-dependent AC conductivity data is ∼1.37 eV. In wider range of frequencies and temperatures, the relative permittivity of approximately 50 to 60 is observed for Ca0.5Th0.5VO4