Identification of a nanosecond isomer of ¹⁶⁴Tb

This letter reports on the identification of a new isomeric state of ¹⁶⁴ 164 Tb ( $$Z=65$$ Z = 65 , $$N=99$$ N = 99 ), which was measured with the DESPEC setup at the GSI Helmholtzzentrum für Schwerionenforschung GmbH following the first relativistic fragmentation of an ¹⁷⁰ 170 Er primary beam. From the time distribution and coincidences of the emitted γ γ rays, the isomer is tentatively assigned to a state with spin-parity (7⁻) ( 7 - ) at an excitation energy of 283.3(2)~keV 283.3 ( 2 ) keV with a half-life of 159(11)~ns 159 ( 11 ) ns . The isomer is interpreted as the π 7/2⁻[523]⊗ ν 7/2⁺[633] π 7 / 2 - [ 523 ] ⊗ ν 7 / 2 + [ 633 ] configuration from the Nilsson orbital systematics. These results represent the first report of γ γ -ray spectroscopy of ¹⁶⁴ 164 Tb, providing insight into the ground-state and low-lying level structure.