Application of the time-of-flight technique for lifetime measurements with relativistic beams of heavy nuclei

A novel method for picosecond lifetime measurements of excited γγ-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 ∼55MeV/u. The beam ions were Coulomb excited to the 21+ 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 γγ-ray decays from the 21+ excited state that occurred before or after traversing the degrader were measured at a different Doppler shift. The γγ-ray spectra were analyzed from the forward ring of the Segmented Germanium Array; this ring positioned at 37∘37∘ simultaneously provides the largest sensitivity to changes in ββ and the best-energy resolution. The ratio of intensities in the peaks at different Doppler shifts gives information about the lifetime if the velocity ββ is measured. The results and range of the application of the method are discussed.