Hydrogenic-Carbon Lamb Shift Studied via Motional Electric Field Quenching of the2S122State

Beams of bare carbon nuclei were produced at 25 and 35 MeV using the Bell-Rutgers tandem Van de Graaff accelerator. Hydrogenic atoms, ${\mathrm{C}}^{5+}$, were formed by electron pickup in dilute argon gas. About 2.2% of the ${\mathrm{C}}^{5+}$ beam is found to be in the metastable $2{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ state. On entering a magnetic field, the metastables are Stark quenched by the motional electric field $\left(\frac{\gamma }{c}\right)\overrightarrow{\mathrm{v}}\times \overrightarrow{\mathrm{B}}$. The quench-radiation decay length was determined by counting ${\mathrm{C}}^{5+}$ Lyman-$\alpha$ quanta as a function of distance traversed in the field. Windowless electron multipliers and thin-window gas-flow proportional counters were used to detect the 33.8-Å radiation. The decay length, as a function of field and energy was used to determine the Lamb shift ($2{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-2\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ splitting) with the aid of Bethe-Lamb quenching theory. The result is 780.1±8.0 GHz. Corrections due to beam deflection, background, $2{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ state mixing, special relativity, and Zeeman effect are considered. Recent calculations are in agreement with the experimental result.