Solving the Puzzles of the Decay of the Heaviest Known Proton-Emitting Nucleus <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Bi</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>185</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math>
D. T. Doherty, A. N. Andreyev, D. Seweryniak, P. J. Woods, M. P. Carpenter, K. Auranen, A. D. Ayangeakaa, B. B. Back, S. Bottoni, L. Canete, J. G. Cubiss, J. Harker, T. Haylett, T. Huang, R. V. F. Janssens, D. G. Jenkins, F. G. Kondev, T. Lauritsen, C. Lederer-Woods, J. Li, C. Müller-Gatermann, D. Potterveld, W. Reviol, G. Savard, S. Stolze, S. Zhu
Abstract
Two long-standing puzzles in the decay of ^{185}Bi, the heaviest known proton-emitting nucleus are revisited. These are the nonobservation of the 9/2^{-} state, which is the ground state of all heavier odd-A Bi isotopes, and the hindered nature of proton and α decays of its presumed 60-μs 1/2^{+} ground state. The ^{185}Bi nucleus has now been studied with the ^{95}Mo(^{93}Nb,3n) reaction in complementary experiments using the Fragment Mass Analyzer and Argonne Gas-Filled Analyzer at Argonne National Laboratory's ATLAS facility. The experiments have established the existence of two states in ^{185}Bi; the short-lived T_{1/2}=2.8_{-1.0}^{+2.3} μs, proton- and α-decaying ground state, and a 58(2)-μs γ-decaying isomer, the half-life of which was previously attributed to the ground state. The reassignment of the ground-state lifetime results in a proton-decay spectroscopic factor close to unity and represents the only known example of a ground-state proton decay to a daughter nucleus (^{184}Pb) with a major shell closure. The data also demonstrate that the ordering of low- and high-spin states in ^{185}Bi is reversed relative to the heavier odd-A Bi isotopes, with the intruder-based 1/2^{+} configuration becoming the ground, similar to the lightest At nuclides.