Theses and Dissertations (Physics)http://hdl.handle.net/10500/30572014-08-28T07:59:55Z2014-08-28T07:59:55ZBound states for A-body nuclear systemsMukeru, Bahatihttp://hdl.handle.net/10500/89092014-04-23T18:38:04Z2012-03-01T00:00:00ZBound states for A-body nuclear systems
Mukeru, Bahati
In this work we calculate the binding energies and root-mean-square radii for A−body
nuclear bound state systems, where A ≥ 3. To study three−body systems, we employ
the three−dimensional differential Faddeev equations with nucleon-nucleon semi-realistic
potentials. The equations are solved numerically. For this purpose, the equations are
transformed into an eigenvalue equation via the orthogonal collocation procedure using
triquintic Hermite splines. The resulting eigenvalue equation is solved using the Restarted
Arnoldi Algorithm. Ground state binding energies of the 3H nucleus are determined.
For A > 3, the Potential Harmonic Expansion Method is employed. Using this method,
the Schr¨odinger equation is transformed into coupled Faddeev-like equations. The Faddeevlike
amplitudes are expanded on the potential harmonic basis. To transform the resulting
coupled differential equations into an eigenvalue equation, we employ again the orthogonal
collocation procedure followed by the Gauss-Jacobi quadrature. The corresponding
eigenvalue equation is solved using the Renormalized Numerov Method to obtain ground
state binding energies and root-mean-square radii of closed shell nuclei 4He, 8Be, 12C, 16O
and 40Ca.
2012-03-01T00:00:00ZStructure of hypernuclei studied with the integrodifferential equations approachNkuna, John Sollyhttp://hdl.handle.net/10500/88282014-04-23T18:26:09Z2012-06-01T00:00:00ZStructure of hypernuclei studied with the integrodifferential equations approach
Nkuna, John Solly
A two-dimensional integrodi erential equation resulting from the use of potential harmonics
expansion in the many-body Schr odinger equation is used to study ground-state
properties of selected few-body nuclear systems. The equation takes into account twobody
correlations in the system and is applicable to few- and many-body systems. The
formulation of the equation involves the use of the Jacobi coordinates to de ne relevant
global coordinates as well as the elimination of center-of-mass dependence. The form of
the equation does not depend on the size of the system. Therefore, only the interaction
potential is required as input. Di erent nucleon-nucleon potentials and hyperon-nucleon
potentials are employed to construct the Hamiltonian of the systems. The results obtained
are in good agreement with those obtained using other methods.
2012-06-01T00:00:00ZTheoretical study of magnetic odering of defects in diamondBenecha, Evans Mosetihttp://hdl.handle.net/10500/63122014-04-23T18:38:36Z2011-11-01T00:00:00ZTheoretical study of magnetic odering of defects in diamond
Benecha, Evans Moseti
Magnetic ordering of dopants in diamond holds the prospect of exploiting diamond’s unique
properties in the emerging field of spintronics. Several transition metal defects have been
reported to order ferromagnetically in various semiconductors, however, low Curie
temperatures and lack of other fundamental material properties have hindered practical
implementation in room temperature spintronic applications. In this Thesis, we consider the
energetic stability of 3d transition metal doped-diamond and its magnetic ordering properties
at various lattice sites and charge states using ab initio Density Functional Theory methods.
We find the majority of 3d transition metal impurities in diamond at any charge state to be
energetically most stable at the divacancy site compared to substitutional or interstitial lattice
sites, with the interstitial site being highly unstable (by ~8 - 10 eV compared to the divacancy
site). At each lattice site and charge state, we find the formation energies of transition metals
in the middle of the 3d series (Cr, Mn, Fe, Co, Ni) to be considerably lower compared to
those early or late in the series. The energetic stability of transition metal impurities across
the 3d series is shown to be strongly dependent on the position of the Fermi level in the
diamond band gap, with the formation energies at any lattice site being lower in p-type or ntype
diamond compared to intrinsic diamond.
Further, we show that incorporation of isolated transition metal impurities into diamond
introduces spin polarised impurity bands into the diamond band gap, while maintaining its
semiconducting nature, with band gaps in both the spin-up and spin-down channels. These
impurity bands are shown to originate mainly from s, p-d hybridization between carbon sp
3
orbitals with the 3d orbitals of the transition metal. In addition, the 4p orbitals contribute
significantly to hybridization for transition metal atoms at the substitutional site, but not at
the divacancy site. In both cases, the spin polarisation and magnetic stabilization energies are
critically dependent on the lattice site and charge state of the transition metal impurity.
By allowing magnetic interactions between transition metal atoms, we find that ferromagnetic
ordering is likely to be achieved in divacancy Cr+2, Mn+2, Mn+1 and Co0 as well as in
substitutional Fe+2 and Fe+1, indicating that transition metal-doped diamond is likely to form
a diluted magnetic semiconductor which may successfully be considered for room
temperature spintronic applications. In addition, these charge states correspond to p-type
diamond, except for divacancy Co0, suggesting that co-doping with shallow acceptors such as
B (
will result in an increase of charge concentration, which is likely to
enhance mediation of ferromagnetic spin coupling. The highest magnetic stabilization energy
occurs in substitutional Fe+1 (33.3 meV), which, also exhibits half metallic ferromagnetic
ordering at the Fermi level, with an induced magnetic moment of 1.0 μB per ion, thus
suggesting that 100 % spin polarisation may be achieved in Fe-doped diamond.
2011-11-01T00:00:00ZAtomic processes in gaseous nebulaeProzesky, Andrihttp://hdl.handle.net/10500/53472014-04-23T18:36:15Z2011-05-01T00:00:00ZAtomic processes in gaseous nebulae
Prozesky, Andri
The atomic physics relevant to gaseous nebulae is critically examined using modelling
software with particular emphasis on radio recombination lines (RRLs). The
theoretical spectral line intensities can be deduced if we know the population structure
of the bound electrons in the gas under non-thermal equilibrium conditions.
The population structure of hydrogen is solved for various environments using a
capture-collision-cascade model that incorporates an ambient radiation eld.
The validity of assuming Case B (Baker & Menzel, 1938) for nebulae is investigated.
It is known that Case B is appropriate for levels with small principal quantum
numbers (n < 40), but this assumption is re-examined for high levels which are
relevant to RRLs.
E ects of an ambient radiation eld on the population structure is examined and
processes that are stimulated by a radiation eld are included in the model. This is
done as a preliminary investigation to extend the model to a photoionization code.
2011-05-01T00:00:00Z