High-field level crossing in atomic hydrogen

In hydrogen, an external magnetic field, which we calculate to be ≈16.65 T, cancels the internal field caused by the electron motion in the magnetic sublevels with mJ=+1/2. This results in an energy-level degeneracy between states with nuclear magnetic sublevels mI of opposite signs. The evaluation of this field has been calculated previously with the use of the low-field quantum numbers F, mF. We show that this calculation is considerably simpler in the high-field mJ, mI representation. A comparison is given with the earlier work.