Low-lying states in $\sideset{^{219}}{}{\mathop {\rm Ra}}$ and $\sideset{^{215}}{}{\mathop {\rm Rn}}$: Sampling microsecond $\alpha$-decaying nuclei

Abstract

Short-lived α-decaying nuclei "northeast" of 208 Pb in the chart of nuclides were studied using the reaction 48 Ca + 243 Am with the decay station TASISpec at TASCA, GSI Darmstadt. Decay energies and times from pileup events were extracted with a tailor-made pulse-shape analysis routine and specific α-decay chains were identified in a correlation analysis. Decay chains starting with the even-even 220 Ra and its odd-A neighbors, 219 Fr, and 221,219 Ra, with a focus on the 219 Ra → 215 Rn decay, were studied by means of α-γ spectroscopy. A revised α-decay scheme of 219 Ra 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.