Lifetime measurements of the2P13state in heliumlike silicon and sulphur

We report measurements of the lifetime of the metastable $2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state in heliumlike silicon and sulphur using the time-of-flight technique. An apparatus was developed suitable for direct beam-foil measurement of mean lives of x-ray emitting states whose lifetimes are in the neighborhood of ${10}^{-12\mathrm{}}$ sec. Silicon beams at 48 and 54 MeV and sulphur beams at 50, 60, and 66 MeV underwent foil excitation in passage through a nickel foil. A high-resolution Doppler-tuned spectrometer was used to study the decay profile of the emitted x rays. The measured lifetimes of the $2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state, (6.35 ± 0.33) × ${10}^{-12\mathrm{}}$ sec and (1.57 ± 0.18) × ${10}^{-12\mathrm{}}$ sec for silicon and sulphur, respectively, are in agreement with theory.