Neutron scattering theory and spectrometers are described and the relevance of neutron scattering to surface science discussed. Low frequency vibrational modes of hydrogeneous ligands were studied, mainly by incoherent inelastic neutron scattering. Complexes containing ethylene were investigated and their torsional vibrations assigned. The in-phase and out-of-phase torsions have been observed in the case of complexes containing more than one ethylene ligand, and models have been proposed for the interaction between the ethylene groups. The experimentally observed frequencies have been expressed in terms of constants derived from these models. π-bonded complexes (π-allyls, norbornadienes and cyclobutadiene iron tricarbonyl) have been studied, their low frequency modes assigned and their effective torsional force constants calculated. However, there remains an anomaly in the assignments of the norbornadiene complexes. Studies of square planar Pd and Pt ammines have shown that there is just a single torsional mode in each case. It has previously been suggested that the NH(_3) ligandsin trans complexes (particularly Pt) could couple via the "d" orbitals. No evidence of such coupling was found. From the momentum transfer dependence of the i.n.s. spectrum, and the temperature dependence of the i.r. spectrum, evidence for a significant metal-metal interaction in cis-Pt(NH(_3))2Cl(_2) was obtained. In the case of sulfur complexes containing NH(_3) and NH(_2) groups, the torsions have been assigned. Comparison of their i.n.s. spectra with that of disilver sulfamide, has shown that the latter does not contain an NH(_2) group. C(_2)H(_4) adsorbed on a silver exchanged zeolite (Ag-13X) at two different coverages was studied. From the observed i.n.s. intensities and shifts on deuteration (C(_2)D(_4) and trans-C(_2)D(_2)H(_2)) assignments of the vibrational modes of the ethylene relative to the surface was possible, in the higher coverage case interaction between ethylenes on two different sites was observed. The i.n.s. spectrum of ethylene adsorbed on the sodium form of 13X was indicative of a much more weakly held species and an analysis of the quasi-elastic scattering confirmed this. I.N.S. spectra of C(_2)E(_2) and C(_2)D(_2) adsorbed on Ag-13X were obtained and the acetylene-surface vibrations were assigned. From the shifts on deuteration it appears that the adsorbed molecule is non-linear. The i.n.s. spectra of C(_2)H(_2) adsorbed on Na-13X was too poorly resolved for definite conclusions to be drawn. Hydrogen adsorbed (at 200ºC) on Pt black was studied in the region 0 → 4000 cm(^-1). The adsorption conditions produced just one surface state (6) and the adsorption was shown to be dissociative. A vibration of the hydrogen, relative to the surface, was observed at 403 cm(^-1). In fact the spectra are best interpreted as being due to co-adsorbed H(^2)O and H. Higher energy peaks were obtained (including one assigned to the V(_2) vibration of water) but could not be definitely assigned. This project is not yet complete and further experimental work is required before full assignments can be made.

The second order potentials method of Bransden and Coleman (1972) has been applied to electron impact excitation of lithium, sodium and helium atoms and to proton impact excitation of helium atoms. The calculations for the e-alkalis are presented in the impact parameter approximation in the energy range 10 - 200 ev., and in the partial wave approximation in the energy range 10-50 ev. On comparing between the two results, it is concluded that the impact parameter approximation is reliable for energies larger than 50 ev. The results for the electron and proton scattering from the helium atoms are presented in the energy range 100 - 1000 ev (kev for proton scattering).

No description available.

This work is concerned with a theoretical description of the scattering of charged particles from a helium target, at non - relativistic velocities. Using a truncated atomic eigenfunction expansion it is necessary at high energies to make some allowance for all the channels not explicitly included in the expansion. This is done by constructing a second order potential matrix. The method is applied to the scattering by helium atoms of electrons between 50 ev. and 1000 ev., and results are presented for elastic scattering and the 2'S and 2'P excitations. It is found that the inclusion of the couplings between these channels and the inclusion of second order terms in the potential, leads to cross sections which are in significantly better agreement with the experimental data. By reversing the sign of the potential, a comparison is made between positron and electron scattering at the same energy.

This thesis contains an account of some of the work carried out by the author whilst at Durham University. The work has been carried out by the High Energy Nuclear Physics Group of the University of Durham in collaboration with similar groups from the Universities of Bonn, Nijmegen, Paris, Turin and Strasbourg. Bubble Chamber analysis is concentrated on those events in which at most there is only one neutral particle involved. The remainder, the NOFIT events, can often amount to a considerable proportion of the total events unless these are analysed they represent a loss in the total knowledge of the physics of the interaction. The events, in a sense, are of lower quality than the normal sets of events that are analysed, since the latter have undergone the fitting process which reduces the effects of errors of measurements and also reduces ambiguities of interpretation. In this thesis events produced by 5 Gev/c positive pions on protons, in which there are two charged secondary particles and two or more neutral particles have been selected for analysis. The problem of ambiguity of identity of the charged secondaries is discussed at length and a successful method has been devised to divide clearly these two pronged events into those with Pπ(^+) and those with π(^+) π(^+) as the two charged secondaries. For each of these groups the effects of measuring errors on the estimated invariant masses is considered in detail and the expected mass resolution in each invariant mass combinations is determined. With the resolution of ambiguity and the calculated precision of mass determination, resonant particle production is sought. Clear signals corresponding to the production of ∆((^++) ɱ , f , A(_1)(^+) and A(_2)(^+) are seen. There is some evidence for the N(^x+) (1700) resonance. The consideration of mass resolution is preceded by a general consideration of the accuracy of the determination of momentum in the chamber.

Radioisotope heat sources and power systems, traditionally fuelled by 238Pu, have been developed and used for spacecraft thermal management and to provide electrical power during many deep space and planetary science missions. The use of fission reactors in space, however, has been limited to high power applications in Earth orbit. Previous ground based research programs conducted by the U.S. Atomic Energy Commission demonstrated the principal of nuclear thermal rocket propulsion but to date, flight heritage of nuclear propulsion has been limited to nuclear-electric propulsion. The development of space nuclear systems and tributary components that are capable of meeting the rigors of space flight is of paramount importance. Performance, lifetime and operational safety under all foreseeable conditions are essential considerations that must be made. The selection of appropriate materials and environmental compatibility is vital to the success of any given design. The ability for radioisotope heat sources to survive the extreme temperatures and mechanical loads associated with launch related accidents, is both legally mandated and necessary for the protection of life and the Earth’s environment. Nuclear fuels for fission systems must provide equal protection during accidents while the integral design ensures that a reactor remains in a safe configuration. A historical overview of nuclear systems for space is presented. Traditional and modern system designs and fabrication techniques are discussed. Applicable solid state and mechanical power conversion methods are described and their performances are evaluated. Consideration is made for the effect of radioisotope selection and heat source encapsulation architecture upon radiation safety. The identification of 241Am as an alternative isotope fuel is made. Other candidate isotopes such as 210Po, 242Cm and 244Cm are assessed. The development of encapsulation methods that are resistant to the extraction and dispersion of the radioactive materials enclosed is increasingly attractive for security reasons. Spark Plasma Sintering (SPS) processes are presented as novel, simple and rapid techniques for the encapsulation of radioisotopic materials within tungsten ceramic-metallic or cermet matrices. Computational modelling via Monte-Carlo simulation has shown that the encapsulation of radioisotopes within heterogeneous tungsten cermet matrices may reduce the neutron, X-ray and Gamma-ray radiation dose delivered to the localised environment. The prevention of fabrication related volatilisation of radioisotopic compounds is fundamental to the success of the encapsulation process. SPS is empirically demonstrated via the use of CeO2 as an inert simulant for radioisotopic compounds such as PuO2, AmO2 and UO2. The chemical compatibility of americium oxides within a tungsten matrix is also demonstrated through pressureless sintering within a Differential Scanning Calorimetric furnace. The techniques developed for radioisotope encapsulation are also demonstrated in context of cermet fuel fabrication for high temperature space power and propulsion reactor systems. The use of tungsten cermet fuels may eliminate material incompatibilities and failures experienced by historical nuclear thermal propulsion programs. Finally, three novel concept applications of nuclear energy as an enabling technology for planetary exploration are presented. Melt penetration of icy surfaces and long range mobility on planetary surfaces is proposed via the use of pulsed high power heat capacitive radioisotope sources. In-situ resource utilization is considered for propellant production. The use of CO2 is proposed as a propellant for a radioisotope thermal rocket in the context of a ‘Mars Hopper’. A CO2 propellant is also considered in the context of a high temperature (3000°C) nuclear thermal propulsion system for a single stage surface ascent vehicle under a Mars sample return mission.

This thesis reports the development and analysis of feature based synthesis of transmission X-ray images. The synthetic imagery is formed through matching and morphing or warping line-scan format images produced by a novel multi-view X-ray machine. In this way video type sequences, which periodically alternate between synthetic and detector based views, may be formed. The purpose of these sequences is to provide depth from motion or kinetic depth effect (KDE) in a visual display; while the role of the synthesis is to reduce the total number of detector arrays, associated collimators and X-ray flux per inspection. A specific challenge is to explore the bounds for producing synthetic imagery that can be seamlessly introduced into the resultant sequences. This work is distinct from the image collection and display technique, termed KDEX, previously undertaken by the Imaging Science Group at NTU. The ultimate aim of the research programme in collaboration with The UK Home Office and The US Dept. of Homeland Security is to enhance the detection and identification of threats in X-ray scans of luggage. A multi-view „KDEX scanner‟ was employed to collect greyscale and colour coded image sequences of 30 different bags; each sequence comprised of 7 perspective views separated from one another by 10. This imagery was organised and stored in a database to enable a coherent series of experiments to be conducted. Corresponding features in sequential pairs of images, at various different angular separations, were identified by applying a scale invariant feature transform (SIFT). The SIFT was additionally bounded by epipolar-line and disparity window criteria. Experiments revealed that around 37% of unfaithful matches were removed. This approach was applied to greyscale imagery and colour coded materials discriminated views, produced by a dual-energy X-ray technique. Two competing approaches namely, direct matching versus material segmentation were developed and tested. The „direct method‟ provided relatively enhanced matching performance. The SIFT matching results are employed by a novel material based morphing to synthesise colour coded X-ray imagery. The technique was designed to conserve the colour coding scheme employed to represent the three different material classes. Error analysis revealed the presence of blurring and ghosting artefacts in the resultant synthetic views. In response a competing translation based image synthesis algorithm was proposed. This rival method reduced the blurring and ghosting artefacts to zero but at the expense of some shape distortion. However, it did provide marginally improved performance when the angular separation between generating views exceeded 50. The fidelity of the synthetic imagery degraded as the angular separation between perspective views was increased. This finding is consistent with the commensurate increase in disparity and therefore dissimilarity between perspective views. The best fidelity intermediary views recorded in this research occurred at 20, which is the minimum angular separation of interest. This result is highly significant as for a given 3D or KDE imaging performance it can reduce the total number of X-ray sensor arrays, collimators and X-ray beams required by a factor of two.

This thesis is concerned with the application of the time-dependent Hartree-Fock method, adopting the Skyrme effective nuclear interaction, to investigate induced nuclear fission processes. Three-dimensional, symmetry-unrestricted constrained Hartree-Fock calculations of ²⁴⁰Pu are presented to obtain the static potential energy surface corresponding to an increasing quadrupole deformation. The time-dependent Hartree-Fock method is applied to evolve in time these deformed states. Different types of fission process are considered. Firstly, the evolution of static configurations which are deformed sufficiently such that they fission upon time evolution, without any external excitation, ('deformation-induced' fission) is investigated. The fragments smoothly form during a gradual evolution of the static state (taking up to ≈ 1500 fm/c for scission to occur), and the resulting fission products agree well with experimental neutron-induced fission data. The kinetic energy released in the process is also shown to compare well to experimental results. Secondly, the effect of providing an external excitation field to static configurations which would not otherwise fission ('boost-induced' fission) is investigated. Upon application of an instantaneous excitation, the evolution of the densities displays a violent oscillatory behaviour as the state evolves to fission, in contrast what was seen for the case of deformation-induced fission. The resulting fission products lie at the edges of typical mass distributions obtained from experiment. The evolution of the densities following the application of a gradual excitation field demonstrates behaviour similar to deformation-induced fission, suggesting that the timescale for the energy deposition has consequences regarding the fission dynamics. The comparison to experimental results following the application of a gradual excitations field is improved compared to an instantaneous excitation. Overall, the results provide a significant exploratory investigation of fission treated as a dynamic process, and suggest that the time-dependent Hartree-Fock method has potential to be applied further to describe the dynamics of nuclear fission.

No description available.

No description available.