  We explain why it is so hard to determine whether neutrinos are Majorana or
Dirac particles as long as the only neutrinos we study are ultra-relativistic.
We then show how non-relativistic neutrinos could help, and focus on the
angular distributions in the decays of an as-yet-to-be-discovered heavy
neutrino $N$. We find that these angular distributions could very well tell us
whether neutrinos are Majorana or Dirac particles.
