Systematic search of chiral doublet bands and role of triaxiality in odd-odd Z = 55 isotopes: cesium 128, 130, 132, and 134

Excited states in four Z = 55 Cs isotopes, namely 128,130,132,134Cs, have been populated via the 122Sn( 10B,4n) fusion-evaporation reaction at 47 MeV, 124Sn(10B,4n) at 47 MeV, 130 Te(6Li,4n) at 38 MeV, and 130Te(7Li,3n) at 28 MeV and 33 MeV, respectively. Beams were provided by the tandem-injected superconducting LINAC at Stony Brook. An array of six Compton-suppressed HPGe detectors was used for the experiments in conjunction with a 14-element BGO multiplicity filter. Pb-backed targets were used in all four experiments.; These odd-odd Cs isotopes have been investigated in search of chiral doublet bands. Two nearly degenerate bands built on the πh _11/2 ⊗ νh_11/2 configuration have been identified in 128,130,132Cs. Systematics of various experimental observables associated with the partner bands are presented. The B(M1)_In/B(M 1)_Out staggering with spin was discovered to be in phase with the B(M1)/B (E2) staggering for the yrast partner band. A core-quasiparticle coupling model employing the Kerman-Klein-Dönau-Frauendorf method was applied to study 128Cs. A triaxial core with an irrotational flow moment of inertia was assumed. The chiral features, as well as previously known experimental characteristics of the πh_11/2 ⊗ νh_11/2 yrast partner band, are well reproduced demonstrating the important role played by triaxiality in the underlying physics in these nuclei.