  We developed a gravity-gradiometer based on atom interferometry for the
determination of the Newtonian gravitational constant \textit{G}. The
apparatus, combining a Rb fountain, Raman interferometry and a juggling scheme
for fast launch of two atomic clouds, was specifically designed to reduce
possible systematic effects. We present instrument performances and show that
the sensor is able to detect the gravitational field induced by source masses.
A discussion of projected accuracy for \textit{G} measurement using this new
scheme shows that the results of the experiment will be significant to
discriminate between previous inconsistent values.
