β -delayed γ -ray spectroscopy of non-yrast states in 138Te near the neutron drip line

We report on the first β -decay data of ¹³⁸Sb to ¹³⁸Te isotopes beyond the doubly magic ¹³²Sn. The parent nucleus was produced by the in-flight fission of a ²³⁸U beam on a ⁹Be target at 345 MeV per nucleon and measured at the BigRIPS separator of the Radioactive Isotope Beam Factory at RIKEN. By using advanced β -γ spectroscopy techniques, the half-life and the tentative spin-parity of ¹³⁸ were measured to be 346(19) ms and (3^-) , respectively. In addition, we observed several low-lying non-yrast states in ¹³⁸Te for the first time. Our data allowed us to rearrange the positions of the first 2⁺ and 4⁺ states in this nucleus and to construct the level scheme of ¹³⁸ in accordance with shell-model calculations. Additionally, we extend energy systematics of Te isotopes within neutron numbers 54 and 86.