Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in Rf 254

Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247(73)μs have been discovered in the heavy Rf254 nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the Kπ=8-, ν2(7/2+[624],9/2-[734]) two-quasineutron and the Kπ=16+, 8-ν2(7/2+[624],9/2-[734])⊗ - 8-π2(7/2-[514],9/2+[624]) four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N=150 isotones. The four-quasiparticle isomer is longer lived than the Rf254 ground state that decays exclusively by spontaneous fission with a half-life of 23.2(1.1)μs. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state

Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in 254Rf

Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247ð73Þ μs have been discovered in the heavy 254Rf nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the Kπ ¼ 8−, ν2ð7=2þ½624; 9=2−½734Þ two-quasineutron and the Kπ ¼ 16þ, 8−ν2ð7=2þ½624; 9=2−½734Þ ⊗ 8−π2ð7=2−½514; 9=2þ½624Þ four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N ¼ 150 isotones. The four-quasiparticle isomer is longer lived than the 254Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2ð1.1Þ μs. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.peerReviewe