DW> Having no charge, neutrons aren't affected by electromagnetic
 DW> radiation.

They have zero net charge, but they do have an electric dipole moment.  In
other words, there is a distribution of charge.  I think (don't know for
sure without reviewing some stuff) that photons that are energetic enough
(low enough wavelength) would interact with neutrons.

->> Say if I had a vacuum tube free floating in space would it
->> exhibit a net acceleration when an electron current flowed
->> through it?

->>  M*i*k*e

 DW> Why should it?

Well, because the conduction electrons are colliding with the atomic nuclei
of the conducting material.  The nuclei recoil from the collison resulting
in an increase in temperature.  Since the charge carrriers are transferring
a nonzero net momentum to the conductor, the conductor should recoil with a
net nonzero momentum.  Or rather, it might, if the conductinmg material
were shapped correctly.

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