The Gamma Cube: a novel concept of gamma-ray telescope

There is a large gap in between the Integral and Fermi spectral domains that is unobserved since the end of the CGRO mission and its Comptel experiment. There were many attempts to fill this gap but no proposal succeeded yet to convince a space agency to plan a mission. There are many reasons contributing to this situation but the most important one is that neither mirrors nor present particle tracking devices are effective at these energies. We propose here a novel design allowing particle tracking for a gamma-ray telescope in the 5-100 MeV band. The idea of this experiment is to image the ionizing tracks of charged particles using the light produced in a scintillator. The experiment operates as a pair creation telescope at high energy and as a Compton telescope with electron tracking at low energy. The telescope features a large scintillator transparent to the produced scintillation light, an ad-hoc optical system and a high resolution and highly sensitive imager. We review the requirements for each of these sub-systems and propose an experiment design taking into account the space constraints. We emphasize the numerous conceptual advantages of such a system as well as the identified difficulties. (authors)