Towards Superheavies: Spectroscopy of 94<Z<98, 150<N<154 Nuclei*

The structure of nuclei that lie at the edges of stability in the nuclear landscape hold the most discovery potential for new physics. While nuclei along the proton and neutron drip-lines reveal stellar nucleosynthesis pathways, very heavy high-Z nuclei, whose fragility stems from enhanced Coulomb repulsion, lead us towards superheavy physics. The island of superheavy nuclei predicted to lie at the next doubly-magic proton and neutron shell-gap is a topic of intense interest in contemporary nuclear structure research. While steady, albeit slow, progress is being made towards synthesizing superheavy elements, their picobarn production cross-sections via fusion preclude the possibility of studying excitations built on them for some time to come. The heaviest nuclei where such spectroscopy is possible is near Z ~100, where the nuclei exhibit surprisingly robust fission barriers up to high angular momenta [1]. These studies provide critical input for constraining theoretical models that attempt to describe the physics of superheavy nuclei, which include single-particle energies, shell-gaps and pairing. While Z ≥ 100 nuclei can be produced and studied via fusion-evaporation reactions, we have concentrated on Z < 100 nuclei, where inelastic and transfer reactions are possible, as these are the heaviest long-lived radioactive nuclei which can be used as targets. Compared to fusion reactions leading to Z ≥ 100, inelastic and transfer reactions with Z < 100 nuclei have comparatively higher cross-sections, and can populate more neutron-rich nuclei. We have focused on studying the highest neutron orbitals with 150 ≤ N ≤ 154.