Question

In what sense one can represent the state of a Silver atom in the Stern-Gerlach experiment as spin up or down ? Can we neglect other degrees of freedom of the Silver atom?

I'm not good at physics, so please let you write detailed description.

Thank you for reading my question.

Answer 1

In case of silver, the valancy is one. It is now known that the orbital and spin magnetic moments of all but the valance electron in a silver atom cancel out. Hence, the orbital angular momentum, and the orbital magnetic moment is zero. Therefore, if spin were not there, a silver beam would not be split when the magnetic field is on. Now, if spin is taken into account, it can take up only two orientations in a magnetic field, corresponding to m_s= ± 1/2. Hence, there would be two sub-beams, which are actually observed. Therefore, the Stern-Gerlach experiment was a direct confirmation of space quantization and the concept of electron spin.