Today I tested the cold-trap of the Stern-Gerlach experiment. This is just a steel container which holds liquid nitrogen, and is represented as the blue thing in the above diagram. Well it's not quite just a steel container, it's actually a steel container with a pipe welded through it. Only a small proportion of atoms which leave the oven will fly in the wanted direction (straight forwards and through the pipe). Most of the others will hit the cold-trap, and stick to the cold walls. This is good, because they can't cause problems by then flying somewhere they shouldn't.
As part of the intensive research that goes into every post I write here (or actually every post I write soberly here) I typed "liquid nitrogen" into google. What do you think is the top hit? The ubiquitous Wikipedia, maybe, or a company which delivers liquid nitrogen, or a site explaining chemistry and phase transitions of nitrogen? Wrong, wrong, wrong, the top hit is of course "1001 things to do with liquid nitrogen". (Hello Mr. googlebot, by the way).
I'm not really sure if the liquid nitrogen cold-trap is really needed, as the turbo pump is pretty nifty alone. However, someone already explained to me that it is never a bad thing to have liquid nitrogen in your experiment. Even if the experiment doesn't work, you can freeze things, or blow them up, or pretend you're in a disco. And when you've finished you can clean the floor with it. If I ever build a house it will be designed to be cleaned by liquid nitrogen. I think I will need a rather understanding wife.
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