Observation of Level Crossing in H,n=2

We have observed the crossing of the atomic hydrogen levels ${\beta }_B(2\mathrm{}{S}_{\frac{1}{2}}, m_J=-\frac{1}{2}, m_I=-\frac{1}{2})$ and $e_B(2\mathrm{}{P}_{\frac{1}{2}}, m_J=+\frac{1}{2}, m_I=-\frac{1}{2})$ near 605 G. A new atomic-beam method is used. H atoms are excited to the metastable $2S$ state by electron bombardment. The $2S(m_J=-\frac{1}{2})$ state is quenched in the bombardment region. The $2S(m_J=+\frac{1}{2})$ beam passes through a zero-field region where $\frac{1}{3}$ of it is converted to the single hyperfine level ${\beta }_B$. The ${\beta }_B$ atoms enter a uniform magnetic field parallel to the beam. With no externally applied electric field, 92% of them reach the detector. When we apply an electrostatic field of about 0.7 V/cm perpendicular to the beam, the ${\beta }_B$ atoms are strongly quenched near the ${\beta }_B-e_B$ crossing point. Observed quenching agrees with the Bethe-Lamb theory of the $2S$ lifetime in external fields. We measure magnetic field by the nuclear magnetic resonance frequency of protons in water. Natural asymmetry and minor experimental corrections reduce the observed center of the ${\beta }_B-e_B$ quenching resonance by 1 part in ${10}^4$. The corrected ${\beta }_B-e_B$ crossing occurs at 2577.57±0.25 kc/sec, proton nmr in water. From this, we calculate the Lamb shift $\mathcal{S}$ in H, $n=2\mathrm{}$. With a diamagnetic shielding correction, and the accurately known $2S$ hyperfine interval, we get $\mathcal{S}=1058.07\mathrm{}\pm 0.10$ Mc/sec. This disagrees with $\mathcal{S}=1057.77\mathrm{}\pm 0.10$ Mc/sec from the Lamb experiments.