First direct observation of isomeric decay in neutron-rich odd-odd ${}^{186}$Ta

Abstract

De-excitation ${\hat{I}}^3$ rays associated with an isomeric state of ${}^{186}$Ta were investigated. The isomers were produced in multinucleon transfer reactions between a ${}^{136}$Xe beam and a natural W target, and were collected and separated by the KEK Isotope Separation System. Two ${\hat{I}}^3$ transitions with energies of 161.1(2) and 186.8(1) keV associated with an isomeric decay were observed for the first time. The half-life of the isomeric state of the neutral atom ${}^{186\mathrm{m}}$Ta was deduced as 17(2) s. Based on the comparison with the previous measurements of the isomeric state using the ESR storage ring at GSI Darmstadt and the coupling of angular momenta of individual particle orbitals in odd-odd nuclei, a decay scheme of ${}^{186\mathrm{m}}$Ta was proposed.