We use a magneto-optical trap to isolate atoms in the metastable state and then measure the rate of 125.0-nm fluorescence due to spontaneous magnetic quadrupole decay. We normalize the overall fluorescence rate from the sample using a “quenching” process in which laser excitation provides a path for prompt decay to the ground state, with each atom emitting one 123.6-nm photon. A single, solar-blind photomultiplier tube is used to detect both the and the quench-induced photons, so that only small corrections relating to spectral response are necessary. We find a spontaneous decay rate of which translates into a lifetime of 28.3(1.8) s. This result is discussed in the context of previous measurements and calculations of lifetimes in the rare gases.
- Received 12 March 2002
- Published 30 July 2002
© 2002 The American Physical Society