Average energy of atoms in the Stern–Gerlach experiment

[Keky]

I have been reading about the Stern–Gerlach experiment and found that the atoms leaving the oven in the experiment have an average energy of 2kT, rather than an energy of 3kT/2 for a gas. I can not find a reason for this higher energy myself and would like suggestions on why this seems to be taken for granted on many reports I have read, and why it is so.

Thanks,

Char.

[peteratcam]

It is because the atoms effuse out of the oven. Effusion should be covered in an undergrad kinetic theory course. The speed distribution in the beam is
\propto v^3exp(-mv^2/2kT)
rather than the usual
\propto v^2exp(-mv^2/2kT)
for Maxwell-Boltzmann.

[Keky]

Thank you for the reply, I shall go read more about effusion.