32 research outputs found
Stopping power and depth dose profile of H+ and He+ ion beams in hydroxyapatite thin films.
Get PDFHadron therapy is a promising technique to treat deep-seated tumors. For an accurate treatment planning, the energy deposition in the soft and hard human tissue must be well known. Water has been usually employed as a phantom of soft tissues, but other biomaterials, such as hydroxyapatite (HAp), used as bone substitute, are also relevant as a phantom for hard tissues. The stopping power of HAp for H+ and He+ beams has been studied experimentally and theoretically. The measurements have been done using the Rutherford backscattering technique in an energy range of 450-2000 keV for H+ and of 400-5000 keV for He+ projectiles. The theoretical calculations are based in the dielectric formulation together with the MELF-GOS (Mermin Energy-Loss Function – Generalized Oscillator Strengths) method [1] to describe the target excitation spectrum. A quite good agreement between the experimental data and the theoretical results has been found. The depth dose profile of H+ and He+ ion beams in HAp has been simulated by the SEICS (Simulation of Energetic Ions and Clusters through Solids) code [2], which incorporates the electronic stopping force due to the energy loss by collisions with the target electrons, including fluctuations due to the energy-loss straggling, the multiple elastic scattering with the target nuclei, with their corresponding nuclear energy loss, and the dynamical charge-exchange processes in the projectile charge state. The energy deposition by H+ and He+ as a function of the depth are compared, at several projectile energies, for HAp and liquid water, showing important differences.European Regional Development Fun
Study of the spin reorientation of (R, R \') Fe11Ti (R = Dy, Tb, R = Gd, Er) and DyFe10Si2.
No full textInvestigamos os fenômenos de reorientação de spins em diversos compostos intermetálicos com a estrutura tipo ThMn IND. 12. Foram estudadas as ligas pseudoternárias (Dy IND. XGd IND. 1-x)Fe IND. 11Ti, (Dy IND. XEr IND. 1-x)Fe IND. 11Ti e (Tb IND. XGd IND. 1-X)Fe IND. 11Ti e o composto ternário DyFe IND. 10Si IND. 2. As técnicas utilizadas neste trabalho foram: suscetibilidade AC em campos baixos, dependência angular da magnetização em amostras orientadas, e espectroscopia Mössbauer. Todas as ligas sofrem uma reorientação de spins do tipo axial-cônico ao abaixar-se a temperatura. Além disto, (Dy IND. XGd IND. 1-x)Fe IND. 11Ti, (Dy IND. XEr IND. 1-x)Fe IND. 11Ti exibem uma reorientação cônico-planar a baixas temperaturas, mas somente para um intervalo limitado de concentrações de Gd ou Er, (Tb IND. XGd IND. 1-X)Fe IND. 11Ti, por outro lado, sofre uma transição axial-planar para x > 0,6, e nenhuma transição para x 0.6, and no reorientation at all for x < 0.6. Theoretical magnetic phase diagrams were calculated with a single-ion model for exchange and crystal-field interactions, showing good agreement with the experimental data. Finally, the DyFe10Si2 reorientation was studied by means of a detailed analysis of the 57Fe hyperfine parameters temperature dependence; in this way the axial-conical transition temperature interval was accurately determined, and the absence of a further conical-planar transition for this compound was confirmed
Study of the spin reorientation of (R, R \') Fe11Ti (R = Dy, Tb, R = Gd, Er) and DyFe10Si2.
No full textInvestigamos os fenômenos de reorientação de spins em diversos compostos intermetálicos com a estrutura tipo ThMn IND. 12. Foram estudadas as ligas pseudoternárias (Dy IND. XGd IND. 1-x)Fe IND. 11Ti, (Dy IND. XEr IND. 1-x)Fe IND. 11Ti e (Tb IND. XGd IND. 1-X)Fe IND. 11Ti e o composto ternário DyFe IND. 10Si IND. 2. As técnicas utilizadas neste trabalho foram: suscetibilidade AC em campos baixos, dependência angular da magnetização em amostras orientadas, e espectroscopia Mössbauer. Todas as ligas sofrem uma reorientação de spins do tipo axial-cônico ao abaixar-se a temperatura. Além disto, (Dy IND. XGd IND. 1-x)Fe IND. 11Ti, (Dy IND. XEr IND. 1-x)Fe IND. 11Ti exibem uma reorientação cônico-planar a baixas temperaturas, mas somente para um intervalo limitado de concentrações de Gd ou Er, (Tb IND. XGd IND. 1-X)Fe IND. 11Ti, por outro lado, sofre uma transição axial-planar para x > 0,6, e nenhuma transição para x < 0,6. A partir de um modelo a um íon para as interações de troca e de campo cristalino, calculamos diagramas de fase magnéticos, que apresentaram boa concordância com os dados experimentais. Finalmente, estudamos a reorientação de spins em DyFe IND. 10Si IND. 2 por meio de uma análise detalhada da variação dos parâmetros hiperfinos do ANTPOT. 57 Fe com a temperatura. Dessa forma, determinamos com precisão o intervalo de temperaturas da transição axial-cônica e confinamos a ausência de uma transição cônica-planar neste composto.We have investigated spin reorientation phenomena in various rare earth-iron intermetallic compounds with the ThMnl2 structure. Pseudoternary (DyxGdl-x)Fe11Ti, (DyEr1-x)Fe11Ti and (TbxGd1-x)Fe11Ti alloys and the ternary compound DyFe10Si2 were studied. The experimental techniques used in this work were: low-field AC susceptibility, oriented-powder magnetization angular dependence, and Mössbauer spectroscopy. All alloys studied undergo an axial-conical spin reorientation on cooling. In addition, (DyxGdl-x)Fe11Ti and(DyEr1-x)Fe11Ti exhibit a conical-planar reorientation at lower temperatures, but on1y for a small Gd or Er concentration range. (TbxGd1-x)Fe11Ti alloys, on the other hand, undergo a single axial-planar transition for x > 0.6, and no reorientation at all for x < 0.6. Theoretical magnetic phase diagrams were calculated with a single-ion model for exchange and crystal-field interactions, showing good agreement with the experimental data. Finally, the DyFe10Si2 reorientation was studied by means of a detailed analysis of the 57Fe hyperfine parameters temperature dependence; in this way the axial-conical transition temperature interval was accurately determined, and the absence of a further conical-planar transition for this compound was confirmed
Analysis of populations of sites of SM2 (Co, Fe) 17 alloys by Mossbauer spectroscopy
No full textRealizamos medidas Mossbauer a temperatura ambiente das ligas de SM IND.2 (CO IND.1-XFE IND.X) ind.17, COM X = 0.1 A 0.6, E DAS LIGAS sm (CO IND.0.90-VFE IND.VCU IND.0.08ZR IND.0.02) ind.8.35, Com V variando de 0.23 A 0.27. Estas amostras foram caracterizadas por difração de raio X. elas apresentaram a estrutura romboédrica do tipo th ind.2zn ind.17 (R3barraM) com os átomos de Fe ocupando quatro sítios cristalográficos distintos todos os espectros obtidos apresentaram desdobramento magnético e um nível de complexidade alto, resultado da sobreposição de quatro sítios distintos de átomos de fe. Os espectros foram ajustados e através desse ajuste determinados os parâmetros hiperfinos associados a cada sítio e suas respectivas populações. Os resultados obtidos das populações dos sítios nas series de compostos Sm ind.2 (CO IND.1-XFE IND.X) ind.17 revelaram a forte preferência dos átomos de FE de ocupar os sítios halteres (2c). No modelo proposto por ray, à função do ZR e o de deslocar pares de FE dos sítios halteres, substituindo-os por pares ZR-vacância. Através dos resultados obtidos pudemos também comprovar esta hipótese através da análise das populações dos sítios das duas series de amostras.Mössbauer measurements were carried out at room temperature for Sm2(Co1-xFex)17 alloys with x=0,1 to 0,6 and Sm2(Co0.9-vFevCu0.08Zr0.02)8.35, with v=0.23 to 0.27. All samples were characterized by X-ray diffraction. They showed rhombohedral structure of th2Zn17 type (R3m), where Fe atoms occupy four crystallographic sites. All spectra showed magnetic splitting and a high complexity resulting from the superposition of four Fe sites. Hyperfine parameters and site populations were obtained by least-squares fitting of the spectra. For Sm2(Co1-xFex)17 alloys, Fe atoms show a strong preference for 2c (dumbbell) sites. In the Zr-containing alloys, on the other hand, this tendency is significantly reduced, confirming A. E. Rays hypothesis on the role of Zr in the improvement of the magnetic properties of these alloys through metallurgical treatments
