Browsing by Subject "Helium"
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Item A New Wide Range Equation of State for Helium-4(2013-08-01) Ortiz Vega, Diego OA multiparametric and fundamental equation of state is presented for the fluid thermodynamic properties of helium. The equation is valid for temperatures from the ?- line (~2.17 K) to 1500 K and for pressures up to 2000 MPa. The formulation can calculate all thermodynamic properties, including density, heat capacity, speed of sound, energies, entropy and saturation properties. A new equation of state is necessary to overcome difficulties associated with the current standard in the asymptotic region between the ? -line and 3 K and also difficulties related to lack of data, extrapolation performance, and accuracy at higher temperatures. Below 50 K, the uncertainties in density are 0.20% at pressures up to 20 MPa. From 50 K to 200 K the uncertainties decrease to 0.05 % at pressures up to 80 MPa. At higher temperatures the uncertainties in density are 0.02 % up to pressures of 80 MPa. At all temperatures and at pressures higher than listed here, the uncertainties may increase to 0.3% in density. The uncertainties in the speed of sound are 0.02%. The uncertainties in vapor pressure are less than 0.02% and for the heat capacities are about 2%. Uncertainties in the critical region are higher for all properties except vapor pressure.Item Finite element solution of the S-limit Schrodinger equation of helium(Texas Tech University, 1979-12) Keller, John WilliamThe Schroedinger equation, for all but the simplest systems, is an elliptic partial differential equation. Almost every method of solution is based on the expansion of the unknown solution in terms of a set of known global functions. Only a few calculations, using strictly numerical techniques based on the finite difference method, have been reported. Shorter cycle times and the increasing memory of computer hardware along with ease of programing provide the major impetus in the investigation of strictly numerical techniques in quantum mechanics. Recently, the Finite Element Method CFEM), which has been used extensively in engineering fields, has been applied to equations of quantum chemistry. However, only three of these calculations involved solution of a partial differential equation (PDE). This paper reports the application of the FEM to a 2-dimensional problem, that of the S-wave limit of the He atom. This problem has also been treated by the numerical finite difference method . The purpose of this study is not to establish that the FEM is an efficient method for solving quantum mechanical problems, but merely to explore the procedure to learn what is involved in its application. This problem has been chosen because its simplicity allows examination of the details of the FEM.Item Microstructural and Mechanical Property Changes in Ion Irradiated Tunsgten(2013-04-08) General, MichaelSustainable fusion power is within reach; however, more research is needed in the field of material science and engineering. One critical component of a fusion reactor is the plasma facing material. Very little literature exists on the sustainability of tungsten as a plasma facing material (PFM). During operation, PFM must withstand harsh conditions with combined effects from high temperature, mechanical stress, irradiation, transmutation, and the production of hydrogen (H) and helium (He) from nuclear reactions. Therefore, this thesis will focus on co-implantation of H and He into tungsten to investigate the mechanical and microstructural material response. For the first part of this study, Molecular Dynamics (MD) was used to qualitatively understand defect migration and mechanical property changes in tungsten. A Brinell hardness test was simulated using MD in tungsten to study the dependence on void size and void density hardness. It was found that hardness changes vary as the square root of the void size and void density. Also the movement of dislocations and its interaction with voids were investigated. For the second part of the study, H and He were co-implanted into tungsten to look at the mechanical and microstructural changes. Hardness changes were measured using a nano-indenter ex-situ on post-irradiated specimen. Results show that the hardness of tungsten after co-implantation is proportional to the square root of the fluence. Additionally, the microstructure of irradiated tungsten samples was investigated by using a Transmission Electron Microscope (TEM). It was observed that the defect microstructure in tungsten, after co-implantation, is quite complex, with a number of intriguing features, such as the presence of the nano-bubbles and dislocation loops. Also it was observed that there was an effect that H has on the nucleation of He nano-bubbles. The results from this work suggest that the effect of co-implanting H and He into tungsten is crucial to fully understand its viability as a PFM.Item Nuclear charge form factors of helium isotopes with configuration mixing(Texas Tech University, 1996-05) Khan, Shamim AkhterNuclear charge form factors of 3He and 4He have been calculated with configuration mixing up to 3hw in the first-order perturbation theory. It is observed that only (2s) excitation contributes to the nuclear form factor, all other states contributions vanish. We have shown that the mixing configuration in 3He and 4He which is due to residual two-body interaction is important. The residual interaction being used is Reid Soft Core type which gives correct excitation energy of 4He of the first excited state. The admixture coefficients of the order of 8% for 3He and 12% for 4He nuclide are obtained. The configuration mixing improves the form factor substantially over the one without any configuration mixing for both 3He and 4He nuclide for low momentum transfer. Short-Range-Correlation (SRC) of Jastrow type when invoked improves the agreement of calculations with the experimental data to some larger momentum transfer but does not reproduce the second minimum. At large momentum transfer the electron scattering from these light nuclide is able to give finer details of the interior features of the nucleons within the nucleus, where quark degrees of freedom seem to be important. D-state with SRC has shown second minimum and third maximum, though much smaller.Item Singlet-triplet mixing in the spectra of excited helium-like ions(Texas Tech University, 1970-05) Parish, Randell MelNot available