Prompt spectroscopy above 2- and 4-quasiparticle K-isomers in ²⁵⁴No

Since the first observation of rotational excitations up to high spins in ²⁵⁴No (Z=102, N=152) which pointed to extra stability against fission in very heavy nuclei, this nucleus has been a gateway for the spectroscopy of superheavy elements. Axially symmetric, deformed prolate shapes, together with valence nucleon orbitals with large projections of the angular momentum onto the symmetry axis, lead to robust K-isomerism in this region. Decay pathways have been mapped out for the 2- and 4-quasiparticle (qp) K-isomers in ²⁵⁴No. Prompt rotational excitations built on K-isomers help identify nucleon orbitals involved in the isomer configurations. These, in turn, provide information on single-particle level energies that are critical for constraining theories of superheavy nuclei. We report on our search for prompt, rotational excitations built on 2- and 4-qp K-isomers in ²⁵⁴No via the ²⁰⁸Pb(⁴⁸Ca,2n) fusion-evaporation reaction, using the Argonne Gas-Filled Analyzer (AGFA) and the GAMMASPHERE array of HPGe detectors, using recoil-decay-tagging techniques.

Work supported in part by USDOE Grant No. DE-FG02-94ER40848 (UML) and Contracts No. DE-AC02-06CH11357 (ANL), and No. DE-AC02- 05CH11231 (LBNL)