  We investigate the sensitivity of the cross section for lepton pair
production off a deuteron target, $\gamma d \to l^+ l^- d$, to the deuteron
charge radius. We show that for small momentum transfers the Bethe-Heitler
process dominates, and that it is sensitive to the charge radius such that a
cross section ratio measurement of about $0.1 \%$ relative accuracy could give
a deuteron charge radius more accurate that the current electron scattering
value and sufficiently accurate to distinguish between the electronic and
muonic atomic values.
