Configuration assignments to isomers in the neutron-richTa186(Z=73)nucleus

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

“…The proposed decay scheme indicates that the K π = 9 + isomeric state decays to the first member of the rotational band of the K π = 5 − ground state. Sood and Gowrishankar suggested K π = 8 − for the isomeric state [18], however our measurements indicate K π = 9 + . They also suggest that a K π = 9 + state is possible with a antiparallel-spin two-quasiparticle configuration π7/2[404] ⊗ ν11/2[615].…”

“…Furthermore, the ratio of the efficiency-corrected peak count of Ta K α X rays to the 161-keV γ rays in Fig. 3 (b) is 0.70 (18). It should be compared to α K .…”

“…They are considered to be due to the single-particle orbitals of the 73rd proton, π7/2 + [404], and the 113th neutron, ν3/2 − [512], respectively. The coupling of the angular momenta of those individual particle states in 186 Ta gives the lower energy state with the parallel-spin configuration [18,30], which is considered as the ground state of 186 Ta. We assigned 6 − and 9 + for the 187-keV excited state and the isomeric state, respectively, based on 5 − of the ground state and the multipolarities discussed above.…”

“…512]}, are located at excited energies between the isomeric state and the ground state [18,30]. However the transition from the isomeric state to those states is strongly suppressed by the large K change ∆K = 7.…”

“…} for the ground state and two isomeric states with the half-lives of 1.54 min and 3.0 min, respectively [18]. In spite of these efforts to understand the isomeric states both in experimental and theoretical studies, they have not been identified yet in terms of their energies, spins and parities by direct measurements of isomeric decays.…”