  Both transport $\tau_{tr}$ and elastic scattering times $\tau_{e}$ are
experimentally determined from the carrier density dependence of the
magnetoconductance of monolayer and bilayer graphene. Both times and their
dependences in carrier density are found to be very different in the monolayer
and the bilayer. However their ratio $\tau_{tr}/\tau_{e} $is found to be of the
order of $1.5 $ in both systems and independent of the carrier density. These
measurements give insight on the nature (neutral or charged) and spatial extent
of the scattering centers. Comparison with theoretical predictions yields that
the main scattering mechanism in our graphene samples could be due to strong
scatterers of short range, inducing resonant scattering, a likely candidate
being vacancies.
