Authors
Wahid, S.; Tandel, S.; Suman, Saket; Srivastava, P. ; Kumar, Anil; Chowdhury, P.; Kondev, F.; Janssens, R.; Carpenter, M. P.; Lauritsen, T.; Seweryniak, D.; Zhu, Shaofei
Abstract
Metastable states with T-1/2 = 8(2) ms in Bi-205 and T-1/2 = 0.22(2) ms in Pb-204, with approximate to 8 MeV excitation energy and angular momentum >= 22 h, have been established. These represent, by up to two orders of magnitude, the longest-lived nuclear states above an excitation energy of 7 MeV, ever identified in the nuclear chart. Additionally, the half-life of the 10.17 MeV state in Bi-206 has been determined to be 0.027(2) ms, the next highest value in this highly excited regime. These observations indicate the emergence of an island of extreme nuclear isomerism arising from core-excited configurations at high excitation in the vicinity of the doubly closed-shell nucleus Pb-208. These results are expected to provide discriminating tests of the effective interactions used in current large-scale shell-model calculations.