A generalised second-quantised notation is used to re-derive Clement's single-particle sum rules, including centre-of-mass corrections. The effect of the repulsive core of the N-N potential on the sum rules is investigated. The corrections produced by the potential core are found to remove ~5% of the sum rule strength to unobservable high-energy states. The second-quantised notation is then used to derive sum rules for two-particle spectroscopic amplitudes. These generalise the result of Bayman and Clement to cover stripping and pickup or nuclei of any spin. Sum rules are derived which relate sums of spectroscopic amplitudes to two-nucleon multipole moments. Predictions are made about these sum rules for transfer of the even type of nucleon in an odd-mass nucleus. The assumptions which have to be made if sum rules are to be applied to two-nucleon transfer data are discussed. Two of these assumptions are unlikely to be valid: the absence of configuration mixing outside a single major shell and the neglect of sequential transfer. However, it is shown that it should still be possible to apply the sum rules without these two assumptions. An exact finite-range DWBA analysis of two-nucleon transfer, with a realistic triton wavefunction, is used in the sum rule analysis of two-neutron transfer on even zirconium isotopes. The fit to the sum rules is not very good and possible reasons for this are discussed. The multipole-moment sum rules are applied to data on various odd-mass nuclei. The results are in good agreement with predictions. The implications for future applications of sum rules to two-nucleon transfer are discussed.

In this work a high voltage electron microscope has been used to produce and image voids in nickel. From these experiments the dislocation bias has been estimated to be 6. 5% and it has been shown that voids also have a bias of about 0. 5% for interstitials over vacancies. A computer program has been written which allows investigation of the strain field existing in the matrix material surrounding voids and bubbles. This program simulates the electron microscope contrast of defects using the two-beam and column approximations and can incorporate realistic pore shapes and strain fields. Results are presented both making the assumption that the strain fields are spherically symmetric and not assuming this constraint. In the latter case a Green's function method has been applied to calculate the defect strain field. This program has been used to study the effects on the image of varying the parameters involved such as defect depth, size and shape, foil thickness and orientation, diffraction vector and deviation from the Bragg position. Images are displayed at the in focus and defocussed image planes and are compared with experimental micrographs of helium bubbles in vanadium and niobium/1% zirconium. . The simulated images agree well with the experimental images and have shown that the extent of the strain contrast is very limited even at large g and with high gas pressure in the pore. Experimental images are often taken with the microscope defocussed in order to enhance the pore edges. It is demonstrated that the small strain contrast will be reduced and may even be Lost completely when the microscope is operated in this condition.

The use of heavy charged particles, such as protons, a-particles and heavy ions, in computed tomography CT is explored. The technique is based on certain physical properties of tissue, the stopping power, which has never been used by any available diagnostic method. Advantages and limitations of this modality are compared to those of X-ray CT. In a detailed study of their interaction with matter, the stopping power and range of charged particles are calculated for different materials of biological interest. A correction to the standard Rossi formula, defining the root mean square angle arising from small-angle multiple scattering, has been derived. The correction is more important for proton and a-particles, particularly when they traverse thick targets. The dose advantage and mass resolution improvement for particles over X-rays are presented quantitatively. The object surface dose, and to a lesser extent the dose at the centre, are remarkably reduced when using charged particles. The effect of small angle scattering on spatial resolution is examined and shown to be improved by employing an exit position detection system. The potential of several particles for computed tomography have been compared. The particles performance together with design considerations indicate the feasibility of a clinically useful particle accelerator which could be implemented for tomography. Simulated data for reconstructed tomography using particles were generated for a head phantom using the general purpose SNARK reconstruction programme, basically designed for X-rays. The programme was implemented to accommodate the way particles convey information about the sample traversed and to account for the influence of the beam divergence. Reconstructions obtained for different particles demonstrate the possibility of producing images of comparable spatial resolution to X-rays, especially with the heavier ions. Charged particle tomography would add a new dimension to the practice of diagnostic radiology for differentiating and imaging the body structure sensitively and relatively safely.

No description available.

Near infrared (JHKL) photometry of RS CVn -type binary systems has been carried out to search for any evidence of circumstellar material in these systems and also for the existence of light variations outside eclipse similar to those observed in the visual. No apparent infrared excess has been observed in fourteen randomly selected systems. Infrared light curves of seven RS CVn binaries (HR 1099, UV Psc, SZ Psc, TY Pyx, AD Cap, HD 5303 and ER Vul) have been obtained, and nearly sinusoidal light variations outside eclipse have been detected for at least HR 1099, SZ Psc and TY Pyx. Irregular light variations have also been observed in the infrared as in the visual, and also a variation of the maximum brightness of HR 1099 and UV Psc. An estimate of the spectral types of the components of the seven extensively observed systems has been made using the current photometric data. Taking into account the current and other observations, possible models have been discussed, with a preference for the spot model. The active component has been shown to be a fast rotator. Another part of this dissertation is near infrared photometry of Wolf -Rayet stars. The most interesting result of these observations was the discovery of an increase in brightness of HD 193793 (WC7 +05) by 2m4 in L' (Xo = 3.8 pm) between June 1976 and August 1977. This has been attributed to the condensation of grains in the star's circumstellar shell.

Recent developements in Computerised Axial Tomography, non-destructive testing of materials, and elemental analysis have encouraged a renewed theoretical and experimental interest in the determination of attenuation coefficients. In particular, the low energy region, < 100 keV, is important because of the rapid changes of mu with absorber atomic number and photon energy. Also, this region is important for medical applications and there is increasing importance being placed upon the limited validity of the mixture rule near absorption edges. This thesis reviews the development of the experimental measurements of mu showing a significant lack of measured data in this energy region. The present state of theoretical knowledge is reviewed in chapter 3 for the most significant modes of interaction, being photoelectric effect and incoherent and Rayleigh scattering. Measurements of mu and mu/p have been made with a Si(Li) detector and a commercial Am-241 radioisotope source. The isotope is distributed in a ceramic matrix and placed in a steel casing with a thin beryllium window permiting low energy emission over 2?. Fifeteen peaks were used in the range 14 to 60 keV. The absorbers used were compounds or elements in either liquid or solid form, ranging from 2 cm of water and various organic solutions to much thinner specimens of compressed powdered solids, and foils of aluminium, silicon and graphite. The transmitted energy spectra were recorded on paper tape and analysed for peak location and integrated peak count on the CDC7600 at the University of London Computer Centre. Subsequent ananlysis and computations were carried out with the Surrey Univerity PRIME computer. Detailed considerations has been given to corrections required to the measured value of mu and mu/p arising from scatter contributions from incoherent and Rayleigh interactions.

This thesis presents infrared and optical photometry of the binary light curves of several cataclysmic variables. The results are discussed in terms of the accepted model of cataclysmic variables, comprising a Roche lobe filling late type secondary and a white dwarf primary. The secondary star loses matter from the inner Lagrangian point and this matter forms an accretion disc around the white dwarf. Our observations have shown that sometimes the late type secondary dominates the infrared luminosity of the binary. With further accurate observations over many cycles such systems will provide an excellent opportunity for the analysis of ellipsoidal variations in late type stars. In other systems the accretion disc spectrum, which current theories predict should vary as v 1/3, dominates the luminosity of the system from the ultraviolet right through to the near infrared. Then our observations, combined with ultraviolet and further optical measurements, allow us to discover the size and outer rim temperature of the accretion disc. Alternatively a combination of the disc spectrum, dominating at short wavelengths and the spectrum of the late type secondary, becoming bright at long wavelengths is observed. Observations of the light curves, simultaneously at infrared and optical wavelengths, then enable us to show that the results can be modelled in terms of an accretion disc of standard brightness distribution being eclipsed by a late type secondary. This provides support for current disc theories. Finally our observations out to 3.6 um combined with 2 - 2.5 um spectrophotometry of one system have shown clearly the presence of a dust cloud around the binary and allowed us to find the temperature of this dust. Similar observations of other systems will be of interest.

This thesis presents a description of the design, development and construction of an Infrared photometer for astronomical use. The primary waveband for the intended system is 8 to 14 microns. The photometer is intended to produce images of extended sources, with a maximum resolution of 16 x 64 pixels (8 x 30 mm), equivalent on a 1.5m, fl3 telescope to an angular resolution of ~ 4 x 1 arc minutes. The method of observation is via the use of a linear strip array of discrete semiconductor detectors. The image field is scanned over the array in order to produce a two dimensional map. A focal plane scanning system has been incorporated into the photometer for this very purpose, making the unit almost totally independent of any specific telescope. Much of the research was centered around the fabrication of the detector array, using Copper Doped Germanium as the basic material, although experiments were carried out with Arsenic Doped Silicon and Lead Tin Telluride. The thesis not only discusses the problems involved in handling these materials, but also includes a section upon the housing of the detectors within a Liquid Helium cooled cryostat. The control system for the Photometer is treated in some depth in order that it may represent a working manual to the operation of the equipment, and therefore includes details of most of the electronic systems relevant to the project. Finally, a brief operational test, carried out on the 1.5m IRFC at Tenerife, is analysed and the results presented. The resultant instrument functioned with an image resolution of 12 working detectors x 64 pixels. The approximate NEP for these detectors was 5 x 10-13 Watts, leading to a Specific Detectivity of ~ 1.0 x 1011 cm (Hz)1/2 W-1 on the Tenerife telescope.

The energy resolution of a proportional counter depends fundamentally on (i) fluctuations in the number of electron-ion pairs produced in the primary ionization and (ii) fluctuations in the size of the subsequent electron avalanche. The avalanche fluctuation is typically 3-4 times larger than the ionization fluctuation. Previous theoretical and experimental work has indicated that fluctuations in both processes can be reduced by improving the efficiency of the ionization mechanisms involved. The ionization efficiency can be increased by means of the Penning effect. Energy spent exciting metastable states is used to increase the ionization yield. This is achieved by introducing a second gas whose first ionization potential is slightly lower than the first metastable level of the main gas. Cross ionization of the admixture gas by metastable states in the main gas can thus occur. With appropriate conditions, the Penning effect becomes the dominant ionization process. The operation of a proportional counter filled with a range of Penning mixtures is investigated experimentally. Penning mixtures are shown to give improved resolution over the more conventional filling of argon-methane. The Penning mixture, argon-xenon, seems to be a practical alternative filling. In order to make rather more fundamental studies of avalanche fluctuations in Penning mixtures, a uniform field chamber is constructed. With this chamber it is possible to directly compare experimental measurements of f (the relative variance of the avalanche size) with values predicted by various avalanche models. (With a cylindrical counter the ionization efficiency varies from cathode to anode and such a comparison is less clear.) The models assume different variations of the local value of Townsend's first ionization coefficient ai with the distance travelled by an electron from the previous ionization. The results obtained are in reasonable agreement with two of the models but these are unsatisfactory from a theoretical point of view. The results are, however, reasonably close to predictions based on experimental measurements of ionization probability.

Travelling Ionospheric Disturbances (T.I.D.s) are perturbations of the ionized regions of the upper atmosphere caused by the passage of acoustic-gravity waves (AGW). These oscillations fall into two distinct classes, labelled large and medium-scale, respectively. Large-scale T.I.D.s propagate equatorwards from the auroral zone and are well correlated with auroral and magnetic activity. The generation mechanism for medium-scale T.I.D.s, however is less well understood. This thesis presents the analysis of observations of medium-scale T.I.D.s taken over a three-year period by means of the HF Doppler technique. Previous T.I.D. observations are reviewed and compared with the present findings. Agreement is found for all T.I.D. characteristics observed, with the exception of the propagation direction, for which no seasonal dependence is evident. As previously reported, no correlation is found between the occurrence of these waves and auroral indices (Ap, Kp, AE). The neutral thermospheric wind can act as an azimuthal filter for AGW through the processes of ducting, critical coupling and reflection. The diurnal rotation of the wind vector thus introduces a similar rotation in the observed T.I.D. propagation direction. This phenomenon is illustrated by observational data and is reproduced theoretically by tracing hypothetical wave paths through a modelled three-dimensional wind profile. A semi-diurnal variation in the propagation direction has been observed which may indicate that lower atmospheric tides may significantly influence upward-propagating gravity-waves. A reverse ray-tracing analysis has been performed to locate the source of the observed waves; for the majority of waves, the generation region lies to the WNW within a range of about 1000 km. Auroral sources do not appear to be important for waves observed at mid-latitudes. A possible source is the meteorological jet stream and a moderate correlation is found between the jet speed at 300 mb and wave occurrence over Leicester.