K. Starosta

A composite chiral pair of rotational bands in the odd-A nucleus 135Nd.

High-spin states in 135Nd were populated with the 110Pd(30Si,5n)135Nd reaction at a 30Si bombarding energy of 133 MeV. Two DeltaI=1 bands with close excitation energies and the same parity were observed. These bands are directly linked by DeltaI=1 and DeltaI=2 transitions. The chiral nature of these two bands is confirmed by comparison with three-dimensional tilted axis cranking calculations. This is the first observation of a three-quasiparticle chiral structure and establishes the primarily geometric nature of this phenomenon.

gamma-ray spectroscopy of neutron-deficient Te-110. I. Low-spin and intermediate-spin structures

Excited states have been populated in 11052Te via the 58 Ni( 58 Ni,α2pγ) reaction at 250 MeV. The Gammasphere γ-ray spectrometer was augmented with ancillary detectors for charged-particle and neutron detection in order to provide clean channel selection. The known level scheme of 110 Te has been greatly expanded with the addition of many new structures. Above spin 8 + , negative-parity structures become yrast. The level scheme of 110 Te below 30ħ is discussed in this paper, including possible evidence for octupole correlations inferred from strong B(E1) strengths.

Chirality and angular momentum coupling in odd-odd nuclei

Chirality in triaxial odd-odd nuclei is discussed as a novel form of spontaneous symmetry breaking in nuclear structure physics. It is shown that the orthogonal coupling of angular momenta for the valence proton, valence neutron and the core rotation, which violates time reversal, results, for specific configurations, from the triaxial shape and irrotational flow moment of inertia. The model calculations are investigated as a study of the characteristics of chirality. Recent progress from experimental studies of the πh11/2νh11/2 partner bands in triaxial A∼130 nuclei is reviewed.Chirality in triaxial odd-odd nuclei is discussed as a novel form of spontaneous symmetry breaking in nuclear structure physics. It is shown that the orthogonal coupling of angular momenta for the valence proton, valence neutron and the core rotation, which violates time reversal, results, for specific configurations, from the triaxial shape and irrotational flow moment of inertia. The model calculations are investigated as a study of the characteristics of chirality. Recent progress from experimental studies of the πh11/2νh11/2 partner bands in triaxial A∼130 nuclei is reviewed.

Recent progress on the investigation of spontaneous formation of chirality in rotating nuclei

Experimental properties of nearly degenerate ΔI = 1 doublet bands, which are built on the same single-particle configuration, are tested against three criteria for spontaneous formation of chirality in nuclei via the coupling of three mutually perpendicular angular momenta. Four representative nuclei, 134 Pr, 130 Cs, 104 Rh and 105 Rh are discussed. The doublet bands in these nuclei exhibit chiral characteristics except for 134 Pr, which shows a significant difference in electromagnetic properties between the two candidate chiral structures.

Collective dipole bands in 110,112Te: Stability against magnetic rotation

Three long, strongly coupled (ΔI=1) sequences have been identified in 110,112Te by using the GAMMASPHERE array in conjunction with the MICROBALL charged-particle array. These bands are interpreted in terms of deformed proton 1-particle–1-hole bands that reach termination at I∼40ℏ. This is the first observation of such collective dipole structures in this mass region. In contrast, many shorter dipole sequences have been associated with weakly deformed structures that generate angular momentum by the shears mechanism (magnetic rotation).

Effect of {gamma} Softness on the Stability of Chiral Geometry: Spectroscopy of {sup 106}Ag

A study of the nucleus 106Ag has revealed the presence of two strongly coupled negative-parity rotational bands up to the 19- and 20- states, respectively, which cross each other at spin I approximately 14. The data suggest that near the crossover point the bands correspond to different shapes, which is different to the behavior expected from a pair of chiral bands. Inspection of the properties of these bands indicates a triaxial and a planar nature of rotation for the two structures. Possible causes for this may be understood in terms of a shape transformation resulting from the large degree of gamma softness of 106Ag. These data, along with the systematics of the odd-odd structures in the mass 100 region, suggest that gamma softness has marked implications for the phenomenon of nuclear chirality.

Smooth terminating bands in {sup 112}Te: Particle-hole induced collectivity

The Gammasphere spectrometer, in conjunction with the Microball charged-particle array, was used to investigate high-spin states in Te-112 via Ni-58(Ni-58, 4p gamma) reactions at 240 and 250 MeV. Several smooth terminating bands were established, and lifetime measurements were performed for the strongest one using the Doppler-shift attenuation method. Results obtained in the spin range 18-32h yield a transition quadrupole moment of 4.0 +/- 0.5eb, which corresponds to a quadrupole deformation epsilon(2)=0.26 +/- 0.03; this value is significantly larger than the ground-state deformation of tellurium isotopes. It was also possible to extract a transition quadrupole moment for the yrast band in Xe-114, produced via the 58Ni (58Ni, 2p gamma) reaction. A value of 3.0 +/- 0.5eb was found in the spin range 16-24h, which corresponds to a quadrupole deformation epsilon(2)=0.19 +/- 0.03. Cranked Nilsson-Strutinsky calculations are used to interpret the results. (Less)

New magnetic dipole phenomena in atomic nuclei

Abstract In recent years a number of nuclear phenomena was discovered that are accompanied by strong magnetic dipole (MI) transitions. Measurements of MZ matrix elements enabled nuclear physicists to deduce new structure information in a model-independent way, since the electromagnetic interaction is well understood. Due to the dominantly isovector character of the electromagnetic MI transition operator (see Appendix A), information on MI matrix elements helps to clarify various aspects of the nuclear isospin degree of freedom (see Appendix B). This is of particular importance as a prerequisite for making full use of newly established or planned radioactive ion beam (RIB) facilities probing nuclei at extreme values of isospin.

High spin states of 135Pr

The mass A = 130 region has been of particular interest both theoretically and experimentally as nuclei in this region are expected to exhibit soft behaviour related to the shape asymmetry parameter γ. The level scheme has been extended considerably up to spin 83/2− with a further possible transition to spin 85/2−.

Sensitive Criterion For Chirality; Chiral Doublet Bands In 104Rh59

A particle plus triaxial rotor model was applied to odd‐odd nuclei in the A ∼ 130 region in order to study the unique parity πh11/2⊗νh11/2 rotational bands. With maximum triaxiality assumed and the intermediate axis chosen as the quantization axis for the model calculations, the two lowest energy eigenstates of a given spin have chiral properties. The independence of the quantity S(I) on spin can be used as a new criterion for chirality. In addition, a diminishing staggering amplitude of S(I) with increasing spin implies triaxiality in neighboring odd‐A nuclei. Chiral quartet bases were constructed specifically to examine electromagnetic properties for chiral structures. A set of selection rules unique to chirality was derived. Doublet bands built on the πg9/2⊗νh11/2 configuration have been discovered in odd‐odd 104Rh using the 96Zr(11B, 3n) reaction. Based on the discussed criteria for chirality, it is concluded that the doublet bands observed in 104Rh exhibit characteristic chiral properties suggesting ...