Performance of CLAIRE, the first balloon-borne ã-ray lens telescope

CLAIRE is a balloon-borne telescope dedicated to validating the concept of a crystal diffraction lens for nuclear astrophysics. For the first time, focusing -rays enters into the domain of the high energy astrophysics. This represents a breakthrough in -ray instrumentation, and will allow unprecedent sensitivities. CLAIRE's first flights occurred on June 15 2000 and on June 14 2001. Here we present its performance during the two flights in terms of pointing accuracy, background noise and estimated efficiency of the lens.