Lifetime measurements of long-lived isomers in Gd using a total absorption detector

Asai, Masato  ; Hayashi, Hiroaki*; Osa, Akihiko  ; Sato, Tetsuya   ; Otokawa, Yoshinori  ; Nagae, Daisuke; Tsukada, Kazuaki  ; Miyashita, Yuji*; Ouchi, Hiroyuki*; Izumi, Sayaka*; Shinozuka, Tsutomu*

We have developed a new method to measure lifetime of long-lived isomers populated through the decay, using a total absorption detector. Using this method, we have determined lifetime of the K isomers in Gd and Gd for the first time. The short-lived neutron-rich nuclei Eu and Eu were produced and mass-separated by the on-line isotope separator (ISOL) at JAEA tandem accelerator facility. Beta- and rays emitted by the decay of Eu were total-absorbed by the detector, and all the events were recorded with time stamps. This method enabled us to determine lifetime of the isomers with more than 100-s lifetime.