# Proton or Electron spin?

1. Nov 1, 2013

### zincshow

If you see a statement like "Spin analysis of H(22S) atom can be achieved through the use of Stern Gerlach interferometry" are they talking about the spin of protons or electrons? Are they perhaps always correlated ie. the same? What about H(22P)?

2. Nov 1, 2013

### clem

The electron magnetic moment is much larger than the proton's,
S-G is related to the electron spin.

3. Nov 1, 2013

### vanhees71

The electron and proton spin are both 1/2. What's measured with the SG apparatus is the spin of the atom as a whole. Of course you are right that in practice it's almost only the electron's spin that's determined, because the magnetic moment of the electron is much larger than the proton's. For the electrons it's
$$\vec{\mu}=-\frac{e}{2m_e} g_s \vec{s}=\mu_B g_s \vec{s}.$$
Here, $g_s \simeq 2$ is the gyromagnetic factor of the electron.
For the proton one has
$$\vec{\mu}_{p}=\frac{e}{2m_p} g_{sp} \vec{s}$$
with the gyromagnetic factor of the proton $g_{sp} \simeq 5.59$.