Evidence for chiral symmetry breaking inEu140?

Abstract

High spin states in $^{140}\mathrm{Eu}$ were populated following the reaction $^{92}\mathrm{Mo}(^{51}\mathrm{V},2pn)$ at a beam energy of $205\phantom{\rule{0.3em}{0ex}}\text{MeV}$ by the ESTU accelerator at the Wright Nuclear Structure Laboratory, Yale University. A total of 5 bands and 69 transitions were assigned to $^{140}\mathrm{Eu}$. The assignments were based on ${K}_{\ensuremath{\alpha}}$ x-ray coincidences and on excitation function measurements. $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence matrices were created. Directional correlation of oriented states analysis, angular distributions, and Compton asymmetry measurements were performed and $B(M1)∕B(E2)$ branching ratios were extracted. The band assignments and structures are discussed in terms of the rotational model and interpreted following a series of cranked shell model and total Routhian surface calculations. In particular, two pairs of bands, one pair based on the $\ensuremath{\pi}{h}_{11∕2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11∕2}$ configuration, the other based on the $\ensuremath{\pi}({g}_{7∕2},{d}_{5∕2})\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11∕2}$ configuration, are identified. These bands show some features expected of either chiral partners or shape coexistence, based on triaxial shapes with $\ensuremath{\gamma}\ensuremath{\sim}\ifmmode\pm\else\textpm\fi{}25\ifmmode^\circ\else\textdegree\fi{}$. Further measurements are required to distinguish between these two possibilities.