X-ray scattering by interstellar dust.

This thesis reports work carried out to make a first observation of x-rays scattered by interstellar dust grains. Initially, important data about the dust, obtained at wavelengths ranging from the infra-red to ultra-violet spectral regions, are discussed in order to establish a useful description of the grains themselves. This is then used to estimate the magnitude and form of the expected x-ray scattering effect which is shown to manifest itself as a diffuse halo accompanying the image of a celestial x-ray source. Two x-ray imaging experiments are then discussed. The first, specifically proposed to look for this effect surrounding a point x-ray source, was the Skylark 1611 project, and comprised an imaging proportional counter coupled to a Wolter type 1 x-ray mirror. This is described up to its final calibration when the basis for a concise model of its point response function was established. However, the experiment was not carried out but its objective and the experience gained during its testing were transferred to the second of the x-ray imaging experiments, the Einstein Observatory, the instrumentation of which was essentially similar. The new instrumental characteristics are described and a model for its point response function is developed. Using this, image data for the point x-ray source GX339-4 is shown to exhibit the sought after scattering phenomenon. The systematic errors inherent in determining the parameters of the responsible dust grains are discussed and the potential of x-ray scattering observations as a probe of the interstellar medium is emphasised.