Modeling and development of soft gamma-ray channeling

We have investigated the use of multilayer thin film structures for channeling and concentrating soft gamma rays with energies greater than 100 keV, beyond the reach of current grazing-incidence hard X-ray mirrors. A suitable arrangement of bent multilayer structures of alternating low and high-density materials will channel soft gamma-ray photons via total external reflection and then concentrate the incident radiation to a point. We describe the properties of W/Si multilayer structure produced by magnetron sputter technique with the required thicknesses and smoothness. We also have developed a flexible set of computer modeling tools to compute the optical properties of multilayer structures, predict the channeling efficiency for a given multilayer configuration and aid in the optimization of potential gamma-ray concentrator-based telescope designs. This modeling includes multilayer optical properties calculated by the IMD software, IDL gamma ray tracing code and a focal plane detector simulation by MEGAlib. This technology offers the potential for soft gamma-ray telescopes with focal lengths of less than 10 m, removing the need of formation flying spacecraft and providing greatly increased sensitivity for modest cost and complexity and opening the field up to balloon-borne instruments.