Low-lying states in Ra 219 and Rn 215 : Sampling microsecond α -decaying nuclei

Short-lived alpha-decaying nuclei "northeast" of Pb-208 in the chart of nuclides were studied using the reaction Ca-48 + Am-243 with the decay station TASISpec at TASCA, GSI Darmstadt. Decay energies and times from pile-up events were extracted with a tailor-made pulse-shape analysis routine and specific alpha-decay chains were identified in a correlation analysis. Decay chains starting with the even-even Ra-220 and its odd-A neighbors, Fr-219, and Ra-221,Ra-219, with a focus on the Ra-219 -> Rn-215 decay, were studied by means of alpha-gamma spectroscopy. A revised alpha-decay scheme of Ra-219 is proposed, including a new decay branch from a previously not considered isomeric state at 17 keV excitation energy. Conclusions on nuclear structure are drawn from the experimental data, aided by Geant4 simulations and a discussion on theoretical calculations.