  The production of light nuclei in relativistic heavy-ion collisions is well
described by both the thermal model, where light nuclei are in equilibrium with
all other hadron species present in a fireball, and by the coalescence model,
where light nuclei are formed due to final state interactions after the
fireball decays. A method is proposed to falsify one of the models. We suggest
to measure a hadron-deuteron correlation function which carries information
about the source of the deuterons and allows one to determine whether a
deuteron is directly emitted from the fireball or if it is formed afterwards.
The $K^-\!-\!D$ and $p\!-\!D$ correlation functions are computed to illustrate
the statement.
