On the Interaction of Cosmic X-Rays with Interstellar Grains

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Abstract
An investigation of the interaction of cosmic X-rays with interstellar grains has been undertaken to determine what might be learned about the grains by observations at X-ray energies. To begin, a review of the extinction of X-rays by grains is given. Then the phenomenon of the X-ray halo is discussed. The many factors which can affect the intensity distribution of the halo are stressed so that in interpreting the observations a good estimate of the grain size and shape can be made. X-ray observations may be useful in identifying light elements in grains. Near the K edge of an element in a grain the scattering is anomalous. The resulting effect on the intensity of the halo is shown to he appreciable in favourable cases. There is also a characteristic fine structure in the K absorption by elements in a solid. Estimates indicate that with large enough optical depths the presence of the lighter elements might be detectable.

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