Levels of187Au: A detailed study of shape coexistence in an odd-mass nucleus

Abstract

The decays of ${}^{187}$Hg (2.2 min; ${J}^{\ensuremath{\pi}}$=13/2${}^{+})$ and ${}^{187}$Hg (2.4 min; ${J}^{\ensuremath{\pi}}$=3/2${}^{\ensuremath{-}})$ have been studied with mass-separated sources at the UNISOR facility. Multiscaled spectra of $\ensuremath{\gamma}$ rays, x rays, and conversion electrons, as well as $\ensuremath{\gamma}\ensuremath{\gamma}t$, $\ensuremath{\gamma}\mathrm{xt}$, $e\ensuremath{\gamma}t$, and $\mathrm{ext}$ coincidences were obtained. Decay schemes have been constructed incorporating $>$99$%$ of the decay intensities assigned to the high-spin and low-spin decays. The $\ensuremath{\gamma}$-ray gated conversion-electron spectra permitted determination of 367 conversion coefficients. A variety of coexisting band structures are established in ${}^{187}$Au. Some of these have near-identical analogs in the heavier odd-mass Au isotopes. The remaining bands reveal new degrees of freedom at low excitation energy in ${}^{187}$Au. Nine electric monopole $(E$0) transitions are observed to deexcite members of these new bands. The work represents an undertaking to achieve a benchmark in complete spectroscopy following radioactive decay. The most notable band structure in ${}^{187}$Au has two bands with identical spins, nearly identical relative energies, and electric monopole transitions connecting the favored members. These bands can be understood as $\ensuremath{\pi}{h}_{9/2}$ and $\ensuremath{\pi}{f}_{7/2}$ intruder configurations coupled to coexisting prolate or near-prolate $(\ensuremath{\gamma}$ $<~$ 20$\ifmmode^\circ\else\textdegree\fi{})$ cores having diabatic configurations that differ only in the number of protons occupying the $N$=5 intruder configurations.