Focusing gamma rays for sub-MeV astrophysics : State of the art of Laue lenses
Nicolas Barrière (IASF, Rome, Italie) — au CESR
Par Francois RINCON - 4/09/2009
Séminaires d’Astrophysique
de l’Observatoire Midi-Pyrénées
Séminaire de
Nicolas BARRIERE
(IASF, Rome, Italie)
16 Septembre 2009 à 11h
CESR
Focusing gamma rays for sub-MeV astrophysics : State of the art of Laue lenses
Despite the soft gamma-ray sky is very rich in physics, the
development of nuclear astrophysics is hampered by technical
difficulties. Observing celestial gamma-ray emission is first and
foremost a matter of extracting a weak signal from an intense and
complex instrumental background. This is partly due to the fact that
all existing instruments are based on concepts where the collecting
area itself is also the sensitive area. In the soft gamma ray domain,
instrumental background in a detector is roughly proportional to its
volume. Hence focusing the celestial signal from a large collecting
area onto a small detector volume would lead to a dramatic improvement
in sensitivity. Focusing gamma rays has long been thought impossible,
but it is now becoming a reality in the 100 keV ? 1 MeV range band,
thanks to Laue lenses.
A Laue lens focuses gamma rays by using Bragg diffraction in the
volume of crystals (i.e. in the Laue geometry). The typical focal
length of such lens ranges between 10 and 100 m, which calls either
for two formation flying satellites or an extensible boom.
In this talk, I will present the state of the art of Laue lenses, and
what we can expect from this technology. Performance of Laue lenses
relies entirely on crystals that compose it, thus the search for
efficient crystals and their characterization in high-energy beams is
of prime importance. I will present our activities for crystals
development, and our latest results obtained at energies up to 816
keV. Crystals measured reflectivities are then input in lens models,
allowing realistic estimates of effective area. In a second part, I
will show reasonably achievable performance (sensitivity, field of
view, imaging) with a telescope featuring a Laue lens of 20m focal
length.
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