Two-photon decay of the 2 (1)S0 state in He-like bromine.

We report a measurement of the lifetime of the 1s2s 1 S 0 state in two-electron Br 33+ . This state decays to the 1s 2 1 S 0 ground state only by the simultaneous emission of two photons. Ions in the 1s2s 1 S 0 level are produced by excitation of energetic bromine ions in a thin carbon foil. The lifetime is determined by measuring the change in the rate of two-photon coincidences as a function of the foil-detector separation. The lifetime measurement yields 39.32(32) ps in agreement with a theoretical value of 39.63(16) ps