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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
291

Polarisation transfer and breakup effects in deuteron induced nuclear reactions

Laid, Abdallah January 1991 (has links)
Optical model studies of low energy (d,d) data show that deuteron-nucleus tensor potentials differ from theoretical model predictions. This suggests that measurement of additional observables, such as Polarization Transfer Coefficients (PTC), are needed to complement the existing data. Whether PTCs can clarify the experimental/theoretical ambiguity has been a matter of controversy. The first part of this thesis addresses this problem. We began by investigating whether the PTC, yields new information concerning the deuteron-nucleus tensor potential. We then examined the extent to which this coefficient can distinguish between the two types of tensor forces, Tr and Tp. We showed that Kyzz is strongly affected by tensor force effects, and that the origin of this sensitivity is the bi-linear combination of scattering amplitudes, Im(Q00Q*21). We also found that, for realistic optical mode parameters, T21 and particularly Kyzz discriminate between the effects of both tensor forces. In the second part of this thesis we study the Weinberg State Expansion model (WSE) for (d,p) reactions. The weakly bound structure of the deuteron suggests the relevance of 3-body effects in the dynamics of deuteron stripping. At intermediate energies, the DWBA provides a much less reliable description of particle transfer reactions. Although the adiabatic theory (ADIA) has provided improvements over the conventional DWBA, recent experimental data suggest that it needs to be refined. The WSE method, in which the dominant contributions from the 3-body channels are explicitly included, is a way to systematically improve ADIA which appears as the lowest order solution in the WSE theory. In implementing the WSE model, we found that as the Weinberg basis size N increases more c.m. n-p relative energies are simulated and readily included into the (d,p) calculations. We also showed that, when performing zero-range WSE calculations for 66Zn(d,p)67Zn (G.S.;5l2-;1 =3) at 25 and 88.2 MeV, the results for dsigma/dO and iT11 converge for N=35. Although 35 Weinberg states were used in constructing the new basis, the reaction calculation reduced to a three coupled channels problem. Our calculations are therefore more efficient than the CDCC methods. The WSE results for dsigma/dO and iT11 were also compared against those of equivalent ADIA and Quasi-ADiabatic (QAD) methods. Our findings reveal that: a) the WSE model provides significant corrections to ADIA's predictions and as such constitutes an elegant mathematical justification of ADIA's ideas; b) the WSE results are overall in good agreement with those obtained using QAD.
292

Theory of proton elastic scattering from finite nuclei at intermediate energies

Crespo, Raquel January 1991 (has links)
The theory of the optical potential for proton scattering at intermediate energies is discussed in detail. The first and second order terms of the KMT multiple scattering optical potentials are calculated for proton scattering from light nuclei in the intermediate energy region (135-300MeV). A momentum space method is developed which allows the study of all the nonlocalities of the potential. A practical numerically stable approximate procedure for the treatment of the Coulomb interaction in momentum space calculations is discussed. The accuracy of the method is compared with other prescriptions in the literature and is shown to produce accurate calculations of scattering observables. The first order term of the KMT optical potential is calculated for proton elastic scattering from 16O and 40Ca. Several approximate treatments of this potential are analysed. In particular it is shown that, using a free nucleon-nucleon transition amplitude with energy fixed at half of the incident beam energy, the optimal factorization provides a good approximation to the full folding potential in the description of the elastic scattering observables. The second order corrections to the KMT optical potential for the elastic scattering of protons from 16o are calculated at 135, 200 and 300 MeV incident energies, paying particular importance to the nonlocalities inherent in the potential. It is shown that these nuclear medium effects result in a significant reduction in the proton-target absorption and modifies the elastic scattering wave function in the interior of the nucleus.
293

Theory of nuclear structure

Dean, David Robert January 1982 (has links)
Inelastic scattering of heavy ions to low-lying collective states is studied. Symmetries of the scattering amplitude are discussed and, in particular, the conditions for the validity of an approximate symmetry property are derived. One condition is that the excitation should be 'adiabatic'. The consequences of this approximate symmetry are given: these include zero vector polarization and a gamma-ray distribution that is symmetric about the direction of recoil. In the more general case, and under strong absorption conditions, the full inelastic scattering amplitude is decomposed into components corresponding to waves turning in opposite directions about the scattering centre. It is shown that this allows a simple interpretation of cross-section structure, particularly in the quasi-classical limit, which is derived and explained. The polarization and γ-ray symmetry angle are also discussed in these terms, and conditions of weaker absorption and Coulomb excitation are considered using the same method. A new proof of the asymptotic form of certain Clebsch-Gordan coefficients is given, and a useful property of spherical harmonics derived.
294

Intermediate energy deuteron elastic scattering from nuclei in a three-body model

Al-Khalili, Jameel Sadik January 1989 (has links)
A study is made of polarized deuteron elastic scattering from 58Ni and 40Ca at the intermediate energies of 400 and 700 MeV. A three-body formalism, based on the Single Folding Model, is used for two sets of Dirac nucleon optical potential parameters. Both potentials are designed to fit the proton elastic scattering observables at half the incident deuteron energy. The two potentials give different predictions for the deuteron scattering observables when used in the Schrodinger equation with relativistic kinematics. Good qualitative agreement with the experimental observables is obtained in both cases for deuteron elastic cross-section, vector (Ay) and tensor (Ayy) analyzing power data of the Saclay group. Quantitative discrepancies between theory and data, particularly in Ayy, suggest mechanisms missing from the simple three-body model. To this end, two sources of spin-dependent effects, Pauli-blocking and breakup of the deuteron to spin-singlet intermediate states, are studied. The role of the spin-dependence associated with Pauli-blocking is studied quantitatively for the d-58 Ni system. The magnitude of the momentum-dependent Tp tensor interaction, is shown to pass through a local maximum in the region of 400 MeV incident deuteron energy. Comparison of numerical calculations with the available experimental data at this energy shows the Pauli mechanism not to be responsible for outstanding discrepancies between theory and data. Breakup effects on the elastic amplitude are studied within a two-step calculation, using two separate high energy methods. The first neglects distortion in the initial, final and intermediate states. Use is made of the Adiabatic approximation, which allows closure over the intermediate breakup states. The effect on the elastic amplitude due to breakup to both triplet and singlet intermediate spin states are calculated. The inclusion of spin-singlet breakup in the model has a very large effect on Ayy, compared with that of spin-triplet breakup. This is attributed to a large contribution from a TL-like tensor interaction in the case of singlet breakup, which is negligibly small in the triplet case. Second order breakup effects are also calculated in Glauber theory, using central potentials. Continuum-continuum coupling effects are found to be negligible at intermediate energies, and thus the two-step calculation is adequate. Glauber theory shows, however, that distortion effects are important at these energies, and suggests the need for a more accurate treatment of spin-singlet breakup effects in future calculations.
295

Measurement of orbital electron capture probabilities in the decay of Ce139

McComb, T. J. L. January 1981 (has links)
No description available.
296

Characterization of thermal and epithermal neutron spectra

Jefferies, Stuart Mark January 1983 (has links)
No description available.
297

Magnetic neutron scattering from transition metal alloys

Burke, S. K. January 1980 (has links)
No description available.
298

Design and Testing of a Coincidence System

Barnes, W. L., Jr. 01 1900 (has links)
This paper is concerned with the design, testing and performance of a coincidence system, the proposed North Texas State College accelerator.
299

ATLAS tile calorimeter online software reorganization and phase-II test-beam campaigns

Hlaluku, Dingane Reward January 2017 (has links)
A thesis presented in fulfillment of the requirements for the degree of: Master of Science in Physics, University of the Witwatersrand, Johannesburg, 2017 / Tile Online software is a set of Trigger and Data Acquisition (TDAQ) required for the operation of Tile. It is built on top of ATLAS TDAQ software following AT LAS management tools and policies. The TDAQ software has been migrated from CMT to CMake, and from SVN to Git, in favor of modern software development tools and procedures. Since Tile Online software follows ATLAS TDAQ, there was a need of reorganization, simplification and clean-up of Tile Online software packages. Tile Online software packages have been migrated and reorganized to the newest ATLAS TDAQ release and the outcome is now used at Point-1 with success. The diagnostic and verification system (DVS) is part of the ATLAS TDAQ online software packages used for configuring and executing tests for TDAQ com ponents, and for advising recovery actions to the TDAQ operator/user. A wrapper way to start complex Tile DVS tests that required two separate programs to run on separate computers has been implemented and tests can now be run from a graphical user interface with detailed presentation of the results by non-experts. The upgrade of the Large Hadron Collider (LHC) to the High-Luminosity LHC will provide significant opportunities to explore new physics beyond the Standard Model. This however presents significant challenges to the detector and the TDAQ systems. The Tile Calorimeter will undergo upgrades whereby the current readout electronics will be completely redesigned and replaced in phase-II to cope with the increased luminosity imposed by the HL-LHC. / XL2018
300

Operation and reactivity measurements of an accelerator driven subcritical TRIGA reactor

O'Kelly, David Sean, January 1900 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

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