A new high-spin isomer in 39 97 Y58

An isomeric state at 3,523 keV excitation energy in⁹⁷Y with a half-life of 144(10) ms has been discovered with the fission-product separator JOSEF. This isomer is depopulated through aγ transition of 162 keV. AnE3 multipolarity for this transition is consistent with the measured conversion coefficients ofα _K =0.98(20) andα _T =1.00(19). Subsequent electromagnetic transitions populate several new⁹⁷Y levels which have high spins. For the isomer the three-quasiparticle configuration πg _9/2?ν(h _11/2,g _7/2)]27/2^? is proposed. TheE3 transition with a strength about 2 single-particle units is supposed to be of the typeh ₁₁ ^2/+1 →d ₅ ^2/?1 . These findings provide evidence for the rapid shape transition atA?100 since they indicate shell-model character of ₃₉ ⁹⁷ Y₅₈ even at high excitation energies while the immediate neighbour ₃₉ ⁹⁸ Y₅₉ contains a rotational band based on a level at 495 keV.