What's the motivation of using silver atoms in the Stern-Gerlach experiment？

[kof9595995]

Historically the experiment was performed on silver atoms, but what's the reason of using silver?

 

[4tp]

Silver has a single valence electron, so with all the other electrons paired up I think with regard to its interaction with a magnetic field it will appear as a spin 1/2 particle. You might say that since Ag has an atomic number of 47, and thus at least one unpaired proton, it should look different than a spin 1/2 particle, but since the gyromagnetic ratio goes like 1/m, this is a small effect. Ultimately nothing is special about Ag, as wiki says the experiment was also performed with H later on.

 

[alxm]

Good question.

There's a lot of serendipity involved here, since it was a successful experiment demonstrating something completely different from what they intended. They didn't know about electron spin, their intent was to measure what they called the 'directional quantization' (richtungsquantisierung) of the electronic 'orbits' within the Bohr-Sommerfeld model, i.e. what we now call the magnetic quantum number.

I think they chose silver simply because it's relatively easy to produce a vapor of silver atoms. That was a lucky choice, since we now know silver is s¹d¹⁰ and has no orbital magnetic moment, so they ended up seeing the electronic spin magnetic moment instead. Then they had luck again, since they first couldn't see the silver deposit on their plate, but happened to be smoking cheap cigars. The hydrogen sulfide from the cigar smoke reacted to form black silver sulfide and "developed" the spots.

So they made the wrong choice when it came to finding what they intended to look at, but the right choice in terms of finding out what the Stern-Gerlach experiment is now famous for having found out - electron spin.

 

[Daverz]

but happened to be smoking cheap cigars

That gave me a belly laugh. I hadn't heard that story before.

 

[kof9595995]

OK,thank you guys.

 

[brickwaller99]

Historically the reason was probably Stern's earlier work with silver gas, measuring mean free path with Elisabeth Borman in 1919, and in 1920 he found the mean thermal velocity for the oven conditions used.

http://physics.oregonstate.edu/~corinne/COURSES/ph425/stern-gerlach.pdf