Enhanced and quenched B(E1) transition rates between parity doublet bands in 227Ra

Abstract

The fast timing (t) method has been used to measure level lifetimes in the parity doublet bands in 227 Ra populated in the decay of 227 Fr. In particular, T 1=2 = 254(9) ps, 236(30) ps, 41 ps, and 16(13) ps have been measured for the 3/2 and 5/2 members of the K = 3/2 band and for the 1/2 and 3/2 members of the K = 1/2 band, respectively. These results indicate surprisingly fast B(E1) rates in this octupole transitional nucleus with the average jD 0 j value of 0.11 efm for the K = 1/2 band and jD 0 j=0.10 efm for K = 3/2 band. The general enhancement (and occasional quenching) of E1 i n tra-doublet and some enhanced extra-doublet transitions in 227 Ra are interpreted within the quasiparticleplus-phonon model with the inclusion of Coriolis coupling. Similar calculations, performed for 223 Ra, are found to be in good agreement with the experimental data.

On the enhanced E1 transitions in the K = 3/2 parity doublet band in 223Ra

“…The beam was mass separated and deposited onto a movable magnetic tape at the measuring station, which was specially designed for the advanced time-delayed βγγ(t) measurements [17]. A more detailed description of the experimental set-up has already been given in [18] (see, for example, fig. 1 in ref.…”

“…In particular, the time calibration of the BaF 2 detector was obtained off-line at ISOLDE using a pre-calibrated source of 140 Ba → 140 La → 140 Ce that was prepared at the OSIRIS separator. A cross-check of time-calibration and symmetry for prompt response, was obtained in situ and in beam from transitions in the decays of 227 Fr → 227 Ra and 227 Rn → 227 Fr which were analyzed by both the slope and centroid shift methods [18,23]. More detailed time calibrations were done at OSIRIS using a variety of beams while maintaining the experimental geometry as close as possible to that at ISOLDE.…”

“…The best description of this dynamical octupole correlations is provided by the standard axially symmetric rotor model (RM) including Coriolis coupling, where the intrinsic degrees of freedom are described by the quasiparticle-phonon model, QPM, (see e.g., refs. [18,19] and citations therein). This approach is discussed in details in ref.…”

“…In the present work we have remeasured lifetimes of selected states in 223 Ra using the advanced time-delayed βγγ(t) method by Mach et al [16,17] at the PSB ISOLDE mass separator at CERN. These measurements are a part of our systematic investigation of the E1 strength in the actinide region [18][19][20][21][22].…”

“…However more probably, the majority of nuclei from this region do not have a stable octupole deformation but the relatively strong octupole correlations lead only to high octupole vibration components in the low-lying states of these nuclei (dynamical description of the octupole correlations) (e.g., refs. [18,19]). The best description of this dynamical octupole correlations is provided by the standard axially symmetric rotor model (RM) including Coriolis coupling, where the intrinsic degrees of freedom are described by the quasiparticle-phonon model, QPM, (see e.g., refs.…”