  We present in this paper a focusing gamma-ray telescope that has only one
goal: addressing the true nature of Type Ia Supernovae (SNe Ia). This telescope
is based on a Laue lens focusing a 100-keV wide energy band centered on 847
keV, which correspond to a bright line emitted by the decay chain of 56Ni, a
radioactive element massively produced during SNe Ia events. Spectroscopy and
light curve measurements of this gamma-ray line allow direct measurement of the
underlying explosion physics and dynamics, and thus discriminate among the
competing models. However reaching this goal the observation of several events
with high detection significance, meaning more powerful telescopes. The
telescope concept we present in this paper is composed of a Laue lens held 30 m
apart from the focal instrument (a compact Compton telescope) by an extensible
mast. With a 3-sigma sensitivity of 1.8\times10-6 ph/s/cm2 in the 3%-broadened
line at 847 keV (in 1Ms observation time), dozens of SNe Ia could be detected
per year out to \sim40 Mpc, enough to perform detailed time-evolved
spectroscopy on several events each year. This study took place in the
framework of the DUAL mission proposal which was recently submitted to ESA for
the third medium class mission of the Cosmic Vision program.
