A NEW TELESCOPE FOR WIDE-BAND GAMMA-RAY ASTRONOMY - THE SILICON COMPTON RECOIL TELESCOPE (SCRT)

A new prototype gamma-ray telescope is described which is sensitive fr om 0.3 to 30 MeV as a Compton telescope and to 100 MeV as a pair detec tor. The Silicon Compton Recoil Telescope (SCRT) uses multilayers of s ilicon strip detectors as a Compton gamma-my converter. Recoil electro ns are tracked with the silicon strip detectors, and their energy loss es and directions are measured. The direction and energy of the Compto n-scattered gamma rays are measured with CsI (Tl)-photodiode detectors . Thus unique directions and energies are found for each incident gamm a my for the first time and without the background of overlapping ring s. SCRT is the first Compton telescope to image the gamma-ray sky dire ctly. It can also detect electron-positron pairs from gamma rays above 5 MeV, extending SCRT's sensitivity to above 100 MeV. Typical resolut ions are 3% (FWHM) in energy at 2 MeV and 0.5-degrees (1 sigma) in ang le. The proposed prototype SCRT instrument has a sensitive area of 650 cm2, a detection efficiency of 3%, a size reduction by about an order of magnitude, and a sensitivity of 15 millicrab for a typical Compton Observatory exposure. SCRT can also measure the polarization of the i ncident gamma rays, especially at low energies and large scattered ang les. Simulation calculations and a discussion of results with a labora tory model are presented.