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

Short-lived alpha-decaying nuclei 'north-east' of ²⁰⁸Pb in the chart of nuclides were studied using the reaction ⁴⁸Ca + ²⁴³Am 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 ²²⁰Ra and its odd-A neighbors, ²¹⁹Fr, and ^221,219Ra, with a focus on the ²¹⁹Ra → ²¹⁵Rn decay, were studied by means of α-γ spectroscopy. A revised α-decay scheme of ²¹⁹Ra 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. (authors)