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## Main Question or Discussion Point

I'm looking for the theoretical calculation of the hyperfine structure transition frequency of Ca-133 which is used in atomic clocks to define the second according to SI-Units. Google, Google... there is a lot about the hyperfine Hamiltonian of hydrogen, but couldn't find none about that of Ca-133. I would like to see how that famous 9,192,631,770 Hz frequency which defines our earthly time standard is calculated through theory. Can anyone help?