How is spin measured?

[Danijel Gorupec]

When I ask google how is the spin angular momentum of an electron measured, it points me to the Stern-Gerlach experiment.

Yet, I figure, it cannot be the only way... As I understand it, the Stern-Gerlach experiment actually measures spin magnetic moment, but I guess there is some other way to measure the spin more directly - how else would we know the 'g' factor of an electron?

[Sensei]

In Zeeman effect spectral lines of some elements, in presence of external magnetic field, are split to couple lines, which depends on spin.

https://en.wikipedia.org/wiki/Zeeman_effect

 

 

[Danijel Gorupec]

1 hour ago, Sensei said:

In Zeeman effect spectral lines of some elements, in presence of external magnetic field, are split to couple lines, which depends on spin.

But this again measures the magnetic moment, no? I don't know how to obtain the g-factor from this data - to obtain the g-factor, shouldn't I also have a direct measurement of the angular momentum?

[swansont]

Electrons placed in a very low-energy cyclotron (often a Penning trap), and measuring the energy (frequency) it takes to excite transitions (spin flips or cyclotron states) 

 

Look for papers by Gerald Gabrielse on the subject, for electrons. 

 

edit: here's a paper on the proton measurement

https://iopscience.iop.org/article/10.1088/1367-2630/14/6/063011/meta

[Danijel Gorupec]

7 hours ago, swansont said:

edit: here's a paper on the proton measurement

https://iopscience.iop.org/article/10.1088/1367-2630/14/6/063011/meta

Beautiful (expressing the g-factor as a ratio of two frequencies where frequencies can be measured very accurately). It does however seem to me that the method assumes certain confidence in equations - that is, that Larmor and cyclotron frequency formulas are both very linear in respect to B.

It seems that spin angular momentum of electron is usually obtained indirectly by measuring magnetic moment and assuming that formulas are right. Still, I did find one example where spin seems to be measured more directly - wikipedia calls it Einstein-de Haas effect: https://en.wikipedia.org/wiki/Einstein–de_Haas_effect

[swansont]

If those equations aren’t right, a lot of spectroscopy falls apart.