Backbending in the pear-shaped Th90223 nucleus: Evidence of a high-spin octupole to quadrupole shape transition in the actinides

Abstract

Relatively neutron-rich thorium isotopes lie at the heart of a nuclear region of nuclei exhibiting octupole correlation effects. The detailed level structure of 223 Th has been investigated in measurements of γ radiation following the fusion-evaporation channel of the 208 Pb( 18 O ,3n) 223 Th reaction at 85 MeV beam energy. The level structure has been extended up to spin 49/2, and 33 new γ rays have been added using triple-γ coincidence data. The spins and parities of the newly observed states have been confirmed by angular distribution ratios. In addition to the two known yrast bands based on a K = 5/2 configuration, a non-yrast band has been established up to spin 35/2. We interpret this new structure as based on the same configuration as the yrast band in 221 Th having dominant K = 1/2 contribution. At the highest spin a backbending occurs around a rotational frequency ofhω = 0.23 MeV, very close to the one predicted in 222 Th, where a sharp transition to a reflection-symmetric shape is expected.

High-resolution (p,t) study of low-spin states in Pu240 : Octupole excitations, αSpieker1, Pascu2, Bucurescu3 et al. 2018Phys. Rev. C221150View full textAdd to dashboardCite

“…A strong argument for the K π = 0 + assignment of Schmorak et al [49] was the observation of a 2 + state above this proposed 0 + state as mentioned earlier. In our (p, t) experiment, an excited state at an energy of 1441.4 keV with an integrated cross section of 2.489 (9) µb was observed. It is described well by a single-step transfer to a 2 + state, see Table II and Fig.…”

“…During the last decade renewed interest to study the octupole degree of freedom in atomic nuclei and, especially, in the actinides has grown, see, e.g., Refs. [1][2][3][4][5][6][7][8][9][10] and references therein. Many of these experimental and theoretical studies were triggered by the observation of the enhanced B E3; 3 − 1 → 0 + 1 value of 42(3) W.u.…”