LAUSR

We report the discovery of a new atomic nucleus 188At, which is the heaviest proton-emitting isotope known to date. The new activity was observed through the 107Ag(84Sr, 3n)188At fusion-evaporation reaction using the focal-plane spectrometer of the gas-filled recoil separator in the Accelerator Laboratory of the University of Jyväskylä, Finland. To fully interpret the experimental data, we have expanded the non-adiabatic quasiparticle model to treat nuclei in the beyond-lead region. The description reproduced the measured decay rate and pointed towards emission from an extremely prolate-deformed state with a dominant s1/2 proton component in the wave function. The Thomas-Ehrman shift can be enhanced in low angular momentum states, but such effects have not been observed in heavy nuclei. The single-proton separation energy of 188At deviates from that extrapolated from the systematics, which can be interpreted as the first evidence of this effect in heavy nuclei. Particle radiation studies have been one of the elementary keystones since the dawn of the nuclear physics. Here, the authors discovered the heaviest proton emitting isotope to date, 188At, that points to a trend change in binding energy systematics, further implying a novel interaction in heavy nuclei.