Observing electron interference through an ordinary macroscopic two-slit experiment would be extremely difficult and would require very slowly moving electrons.  (Slow for an electron means < 10^3 m/s.)

 
How slowly would electrons have to move through slits spaced 6.53 μm apart in order for the first angular displacement from the central interference maximum to where we observe no electrons to be 12.3 degrees?  (Answer in m/s.)