g-factor of a tightly bound electron
  We study the hyperfine splitting of an electron in hydrogen-like $^{209}Bi ^{82+} $. It is found that the hfs energy splitting can be explained well by considering the g-factor reduction due to the binding effect of a bound electron. We determine for the first time the experimental value of the magnetic moment of a tightly bound electron. 
Tomoko Asaga, Takehisa Fujita and Makoto Hiramoto