Using the fusion-evaporation reaction ${}^{96}\mathrm{Ru}({}^{58}\mathrm{Ni},p4n){}^{149}\mathrm{Lu}$ and the MARA vacuum-mode recoil separator, a new proton-emitting isotope ${}^{149}\mathrm{Lu}$ has been identified. The measured decay $Q$ value of 1920(20) keV is the highest measured for a ground-state proton decay, and it naturally leads to the shortest directly measured half-life of ${450}_{-100}^{+170}\mathrm{ns}$ for a ground-state proton emitter. The decay rate is consistent with $l_p=5$ emission, suggesting a dominant $\pi h_{11/2}$ component for the wave function of the proton-emitting state. Through nonadiabatic quasiparticle calculations it was concluded that ${}^{149}\mathrm{Lu}$ is the most oblate deformed proton emitter observed to date.

• Received 15 December 2021
• Revised 2 February 2022
• Accepted 22 February 2022

DOI:https://doi.org/10.1103/PhysRevLett.128.112501