  Electric quadrupole (E2) moments and transitions provide measures of nuclear
deformation and related collective structure. However, matrix elements of the
E2 operator are sensitive to the nuclear wave function at large distances and
are poorly convergent within the ab initio no-core shell model approach. We
demonstrate for the first time that the ratio of neutron to proton quadrupole
transition matrix elements, Mn/Mp, is well-converged in the ab initio no-core
shell model and provides a new and robust tool for comparing with experimental
results. We find that our parameter-free results for Mn/Mp for the carbon
isotopes and 10Be compare well with experiment, where available, and offer new
insight into the quadrupole dynamics of nuclear response.
