Quenched E1 transition rates in 231Th Original Research Article

The fast timing βγγ(t) method has been used to measure lifetimes of the low-lying levels in 231Th populated in the β− decay of 231Ac. The half-life of the View the MathML source band-head at 185.7-keV was measured as View the MathML source, yielding D0 = 1,76(8) × 10−2e·fm and 1.65(6) × 10−2e·fm for the E1 transitions to the View the MathML source and View the MathML source members respectively of the View the MathML source ground state band. Furthermore, View the MathML source were measured for the View the MathML source band-heads at 221.4- and 247.6-keV, and View the MathML source for the View the MathML source and View the MathML source states at 554.7- and 593.6-keV, members of the View the MathML source band. The latter results consistently yield D0 values of the order of 1.1 × 10−2e·fm for three transitions connecting the View the MathML source bands. The observed transition rates have been interpreted within the quasiparticle-phonon model with the inclusion of Coriolis coupling.