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Session 10 - Studies of Black Holes.
Display session, Monday, June 09
South Main Hall,
The development of X-ray optics for the 40 - 100 keV energy range is extremely important. A focusing system is necessary to resolve crowded regions, to provide improved sensitivity, and to provide the deep sky images necessary to make the next great step forward in this energy range. Such a step was ably demonstrated by the success of the Einstein and ROSAT observatories. The X-rays that are focused by these systems are reflected at grazing incidence, and the maximum graze angle for gold at which optimal reflectivity is obtained at 2 keV is about 2 degrees. But, the critical angle of reflectivity decreases linearly as the energy increases for ordinary metal surfaces which has an adverse impact on the design of a focusing system for higher energy X-rays. At least 3 things are negatively affected: (a) the field of view (FOV) is decreased; (b) the projected area of an individual mirror element is decreased; and (c) the focal length for a fixed diameter system is increased. In order to combat these effects, mirrors coated with multilayers have been designed. It is theoretically possible to increase the graze angle by coating the mirror surface with a graded d-spacing such that the spacings closest to the vacuum reflect the least penetrating X-rays and those closest to the supporting substrate (the original mirror surface) reflect the most penetrating X-rays. The ability to produce a coated mirror with close to theoretical performance is, however, technically challenging. We describe our approach to the fabrication of a system designed for 40 - 100 keV that is based on electroforming technology. We also describe some of the general considerations that must be taken into account when fabricating a viable mirror.
Program listing for Monday