  We propose a new method to determine the spatially or impact-parameter
dependent nuclear parton distribution functions (nPDFs) using the double parton
scattering (DPS) processes in high-energy heavy-ion (proton-nucleus and
nucleus-nucleus) collisions. We derive a simple generic DPS formula in nuclear
collisions by accommodating both the nuclear collision geometry and the
spatially dependent nuclear modification effect, under the assumption that the
impact-parameter dependence of nPDFs is only related to the nuclear thickness
function. While the geometric effect is widely adopted, the impact of the
spatially dependent nuclear modification on DPS cross sections has been
overlooked so far, which can, however, be significant when the initial nuclear
modification is large. In turn, the DPS cross sections in heavy-ion collisions
can provide useful information on the spatial dependence of nPDFs. They can be,
in general, obtained in minimum-bias nuclear collisions, featuring the virtue
of independence of Glauber modeling.
