Evidence for octupole correlations inBa124,125

Abstract

The γ decay of the nuclei 124,125 Ba has been investigated by means of the EUROBALL spectrometer, coupled to the DIAMANT array of charged-particle detectors, using the reaction 64 Ni + 64 Ni at E beam = 255 and 261 MeV. In the nucleus 125 Ba six new E1 transitions have been found to link opposite-parity bands currently interpreted as νd 5/2 (+g 7/2 ), νh 11/2 structures. The previously unknown J π = 3 − level in the nucleus 124 Ba has also been identified; its excitation energy is accurately reproduced by a microscopic calculation including octupole correlations. Both issues are bolstered by sizable B(E1)/B(E2) ratios.

Multi-quasiparticle γ-band structure in neutron-deficient Ce and Nd isotopes

“…For 134 Ce, the neutron-aligned band (1, 2n) crosses the ground band (0, 0) at I = 8, and this band is yrast up to I = 16. Above this spin value, it is noted that the 4-qp band (2,4) with both protons and neutrons aligned becomes favored.…”

“…(1), are obtained by specifying different values for the K-quantum number in the angular-momentum projector in Eq. (2).…”

“…High-spin band structure in this mass region has been experimentally investigated through heavy-ion-induced reactions (see, for example, refs. [1,2,3,4,5]). Along with these studies, many low-lying non-yrast states have also been investigated in the β-decay spectroscopic methods [6] and Coulomb excitations of stable as well as radioactive ions [7,8,9].…”

Evolution of deformation in neutron-rich Ba isotopes up to A=150

“…The absolute γ -ray intensities were determined using, as normalization, the adopted absolute intensities of both daughter and granddaughter isotopes I abs ( 148 La; 133.5 keV) = 3.9(1)% [21] and I abs ( 148 Ce; 158.5 keV) = 56(1)% [22], assuming no feeding to the ground state of 148 Ce from the 148 La decay. For the 141.6-keV transition a theoretical conversion coefficient of 0.574 (8) has been employed, using BRICC [23], corresponding to a pure E2 multipolarity. The conversion coefficient for 148 Cs → 148 Ba.…”

“…It is noted that stronger octupole correlations are seen in the lightest A = 112-114 and heaviest elements of the chain, starting from A = 144, which corresponds to the well-known region of octupole deformation N = 56 and N = 88 [2]. Low-lying negative-parity states have also been found in [122][123][124][125][126] Ba, whose character is understood in terms of octupole correlations [8].…”