Measurement of the lifetime of a metastable excited state in Bi-

The lifetime of the P-3(0) state of Bi- has been measured by selective photodetachment in a cryogenic ion-beam storage ring. By measuring the lifetime as a function of applied laser powers and extrapolating to zero laser power, a lifetime of 16.0 +/- 0.5 s is deduced for electric quadrupole decay of the excited state to the ground sate. The result provides a stringent test of recent state-of-the art theoretical calculations.