(EC/β⁺) Decay of Neutron Deficient Nuclide ¹²⁹Ce

Abstract: The nuclide ¹²⁹Ce was produced by a (¹⁶O,4n) reaction with an enriched ¹¹⁷Sn target. With the aid of a helium-jet tape transport system, the reaction products were transported to a shielded location,where Ce samples were prepared after chemical separation. The neighboring isotopes of ¹¹⁷Sn,¹¹⁶Sn and ¹¹⁸Sn,were also bombarded with ¹⁶O beam. Different isotopes of Ce were further separated by comparing the products in the above three reactions. An activity with a half life of 4.1 min in the chemically purified cerium samples was identified as ¹²⁹Ce. Based on X-γ-t and γ-γ-t coincidence measurements, the EC/β⁺ decay scheme of ¹²⁹Ce, including 51 γ lines,was proposed. Using the observed growth decay curve of an intense 278.6keV γ line of ¹²⁹La decay, the β feeding branch from the ground state of ¹²⁹Ce directly to the ground state of ¹²⁹ La was estimated to be (26±7)%. In addition, the γ spectra gated by both La-K_α-X ray and intense 68.2keV γ ray of ¹²⁹Ce decay as well as the time spectra of typical γ rays were also presented here.