  We study the charge and mass distributions within a nucleon and compute the
associated squared radii based on a potential model approach. Different
constituent quark configurations such as $\Delta$, $Y$, and quark-diquark are
considered and compared, with model parameters calibrated by experimental
measurements of the proton and neutron charge radius. The results suggest that
while the charge radius is dictated by quark dynamics, the mass radius is
strongly influenced by nonperturbative QCD contributions to a nucleon's mass
that are not sensitive to the constituent quarks. As a result, the mass radius
could become substantially different from the charge radius. The obtained
nucleon mass distributions of different configurations are further used for
simulations of the initial conditions in heavy ion collisions. The computed
eccentricities $\varepsilon_2$ and $\varepsilon_3$ are found to demonstrate a
considerable sensitivity to the input nucleon profiles, especially to the mass
radius in the peripheral region as well as for systems with fewer participants.
