The Study of Exotic N ≈ 82 Nuclei Using the Daresbury Recoil Mass Separator

Experiments using the Daresbury Recoil Mass Separator have identified microsecond isomers in the exotic N = 82, 83 nuclei, 153Yb, 153Lu, 154Hf, and have established their decay schemes. The results for 153Lu and 154Hf, together with those for lighter N = 82 isotones, provide an outstanding illustration of the dependence of E2 transition rates between J n states on the sub-shell occupation, and demonstrate that half-filling of the π h 11/2 subshell in the N = 82 series occurs just below Z = 71 153Lu. The result for the isomer in the even-odd N = 83 nucleus 153Yb shows that the isomerism results from a low-energy E2 transition, rather than an E3 transition as in lighter N = 83 even-odd isotones, which is another consequence of the π h 11/2 subshell being about half-filled. Furthermore, the long-lived isomer observed in the odd-odd N = 83 nucleus 154Lu also reflects that the π h 11/2 subshell is close to being half-filled.