  A novel method for picosecond lifetime measurements of excited gamma-ray
emitting nuclear states has been developed for fast beams from fragmentation
reactions. A test measurement was carried out with a beam of 124Xe at an energy
of ~55 MeV/u. The beam ions were Coulomb excited to the first 2+ state on a
movable target. Excited nuclei emerged from the target and decayed in flight
after a distance related to the lifetime. A stationary degrader positioned
downstream with respect to the target was used to further reduce the velocity
of the excited nuclei. As a consequence, the gamma-ray decays from the 2+
excited state that occurred before or after traversing the degrader were
measured at a different Doppler shift. The gamma-ray spectra were analyzed from
the forward ring of the Segmented Germanium Array; this ring positioned at 37
deg. simultaneously provides the largest sensitivity to changes in velocity and
the best energy resolution. The ratio of intensities in the peaks at different
Doppler shifts gives information about the lifetime if the velocity is
measured. The results and range of the application of the method are discussed.
