Chiral Degeneracy in TriaxialRh104

Chirality or handedness is a property that has im- portant consequences in fields of science as diverse as biology, chemistry, and physics. In nuclear physics, the coupling of three mutually perpendicular angular momenta induces structure effects due to chirality (1). Interesting chiral properties were observed for the �h 11=2 �h 11=2 configuration of proton (� ) and neutron (� ) single particle levels in triaxial odd-odd nuclei in the A 130 mass region of the chart of atomic nuclei. It is important to show that these chiral symmetry properties are of a general nature and not related only to a specific nuclear mass region. The purpose of this study is to investigate a different region of triaxial nuclei, which necessarily involves a different configuration, to examine the general aspects of chirality in nuclei. The best chiral properties observed to date were discovered in the 104 Rh nucleus involving theg 9=2 �h 11=2 configuration where the valence proton and neutron play opposite roles to those in the A 130 region. Doublet rotational bands related to nuclear chirality were observed in odd-odd nuclei having triaxial shapes. Nuclear chirality results when the angular momenta of the valence proton, the valence neutron, and the core rotation tend to be mutually perpendicular. This occurs when high-j particlelike and holelike orbitals align their angular momenta along the short and long axes of nuclear deformation, respectively, minimizing the interaction energy, and the core-rotation angular momentum is ori- ented along the intermediate axis because it has the largest (irrotational flow) moment of inertia. The result- ing aplanar total angular momentum can be arranged into a left- or a right-handed system, which differs by intrinsic chirality; the two systems are related by the chiral operator, a combination of time reversal and rota- tion by 180. When chiral symmetry is thus broken in the intrinsic frame, the necessary restoration of the symme- try in the laboratory frame manifests itself as degenerate doubletI 1 bands from the doubling of states. The merged states combine the left- and right-handed systems in a way that satisfies the laboratory chiral symmetry requirement. Effects of chirality for odd-odd nuclei were first ob- served in the A 130 region where triaxial deformations were expected. Two near degenerate bands in 134 Pr (2) were observed; microscopic calculations carried out us- ing 3D tilted axis cranking resulted in triaxial deforma- tions and chiral solutions over an extended frequency (spin) range for theh 11=2 �h 11=2 configuration (3). Subsequently, experiments on N 75 isotones (4) of 134 Pr and neighboring isotones (5) revealed near degen- erate partner bands of theh 11=2 �h 11=2 yrast bands, suggesting an island of chirality near A 130. Since the 134 Pr nucleus showed the smallest band separation, a GAMMASPHERE experiment (6) was performed which considerably extended the doublet bands showing the levelsE 50 keV apart at spin I 15 �