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Hyperfine





THEORY

According to classical thinking, the electron moving around the nucleus has a magnetic dipole moment, because it is charged. The interaction of this magnetic dipole moment with the magnetic moment of the nucleus (due to its Spin ) leads to hyperfine splitting.

However, due to the electron's spin, there is also hyperfine splitting for s-shell electrons, which have zero orbital angular momentum. In this case, the magnetic dipole interaction is even stronger, as the electron probability density does not vanish inside the nucleus (~r=0~).

The amount of correction to the Bohr Energy levels due to hyperfine splitting of the hydrogen atom is on the order of

: rac{m}{m_{ m p}} \alpha^4 m c^2

where
:~m~ is the mass of an electron,
:~m_{ m p}~ is the mass of a proton,
:~\alpha~ is the Fine Structure Constant ~(~\alpha \approx 1/137.036~)~, and
:~c~ is the Speed Of Light .

For atoms other than hydrogen, the Nuclear Spin ec{I} and the Total Electron Angular Momentum ec{J} = ec{L} + ec{S} get coupled, giving rise to the total angular momentum ec{F} = ec{J} + ec{I}.
The hyperfine splitting is then
:\Delta E_{ m hfs} = - ec{\mu}_I ec{B}_J = rac{a}{2} F(F+1) - I(I+1) - J(J+1) ,
where
:a = rac{g_I ec{\mu}_{ m N} ec{B}_J}{\sqrt{J(J+1)}},
: ec{\mu}_{ m N} the Magnetic Dipole Moment of the nucleus, and
: ec{B}_J is the atomic Magnetic Field .