High-spin isomers in Rn-212 in the region of triple neutron core-excitations

摘要

The level scheme of Rn-212 has been extended to spins of similar to 38h and excitation energies of about 13 MeV using the Hg-204(C-13, 5n)Rn-212 reaction and gamma-ray spectroscopy. Time correlated techniques have been used to obtain sensitivity to weak transitions and channel selectivity. The excitation energy of the 22(+) core-excited isomer has been established at 6174 keV. Two isomers with tau = 25(2) ns and tau = 12(2) ns are identified at 12211 and 12548 keV, respectively. These are the highest-spin nuclear isomers now known, and are attributed to configurations involving triple neutron core-excitations coupled to the aligned valence protons. Semi-empirical shell-model calculations can account for most states observed, but with significant energy discrepancies for some configurations. (c) 2008 Elsevier B.V. All rights reserved.