Crystal Diffraction Lens Telescope For Focusing Nuclear Gamma Rays PDF Download

A new method has been devised for focusing and imaging the radiation from sharp-line sources of x-rays and gamma-rays, which makes use of variable-metric diffraction crystals. A variable-metric diffraction crystal is one in which the spacings between the crystalline planes is varied as a function of position in the crystal by either the application of a thermal gradient or by changing the composition of a two component or multiple component crystal. This change in planar spacing changes the Bragg diffraction angle for monochromatic radiation as a function of position in the crystal and makes it possible to obtain focusing and in some cases imaging of a sharp-line point source or parallel beam source. This new approach to focusing x-rays and gamma-rays is used to design a number of gamma ray telescopes suitable for focusing the 511 keV annihilation radiation from the strong source of the center of our galaxy. The new designs are surprisingly efficient with approximately 20% of the radiation incident on the variable-metric diffraction crystals being focused on the image spot. Crystals of Ge, Ge + Si, Si, and quartz are used with mosaic widths of 10 arc sec. The size of the telescope can be scaled up or down without affecting the angular resolution or the energy resolution. The largest model described is 50 m long and has 10 crystal diffraction ring assembles with radii between 71 and 200 cm. The total area of the diffraction crystal is 24,610 cm2 and the effective area (total x diffraction coefficient x transmission) is 4745 cm2. An example of a smaller telescope is also given that is only 12.5 m long and has an effective area of 297 cm2.