Isomers in three doubly odd Fr-At-Bi α-decay chains

The ²⁰⁶→²⁰²At→¹⁹⁸Bi, ²⁰⁴→²⁰⁰At→¹⁹⁶Bi, and ²⁰²→¹⁹⁸At→¹⁹⁴Bi a-decay chains have been studied by standard spectroscopic techniques using an on-line isotope separator. All the studied doubly odd isotopes have at least two isomers, which decay by a combination of the following decay modes: a emission, β⁺/EC (electron capture) decay, and internal transition (IT). The internal transition, a highly retarded E3, is the j-forbidden transition between the [{π}h9/2{}{ν}i13/2{]}₁₀^{{{-}}}and the [π{h}9/2ν{f}5/2]₇⁺ states. The B(E3) values of these IT's together with their energy behavior as a function of the neutron and proton number, compared to the energy difference between the 13/2⁺({ν}i13/2) and 5/2^-({ν}f5/2) states in the odd-mass Pb isotones, indicate that these proton-neutron-coupled states have a rather pure shell-model character.