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Excited states in 171Ir have been observed for the first time. Gamma-rays were assigned to the nucleus by the recoil-decay tagging method. The ground-state band has a structure consistent with an h 11 2 proton coupled to a core of large triaxial deformation. At high spins, a bandcrossing occurs which is interpreted as a change in shape to a prolate deformation. Band-mixing calculations are performed for 171–175Ir. These show that shape-coexistence between triaxial and prolate states in these nuclei follows the same systematics found in their Pt and Os neighbours. The systematics are also compared with deformations calculated for 171–179Ir using the code “Ultimate Cranker”. Dipole bands were also observed, but tilted axis cranking calculations suggest that they are associated with a collective rotation.

Yrast states of Sb-106 have been investigated in the Fe-54(Ni-58, alpha pn) reaction using in-beam gamma-spectroscopic methods and in the Cr-50(Ni-58,pn) reaction performing delayed gamma and conversion electron studies. A new isomeric state was found at 103 keV with t(1/2) = 232(21) ns. The number of start's and transitions in the proposed level scheme have been doubled. The experimental results are discussed within the framework of the shell model. [S0556-2813(99)08502-7].

Recent results on the high-spin states of a range of mid- shell nuclei are presented. Coulomb energy differences (CEDs) as a function of spin have been deduced for the mirror pairs and . A quantitative understanding of the variation of the observed CEDs at high spin is presented in terms of rotational alignment and band-termination effects and we show how the shape-change of the nucleus affects the CED. The experimental results for the CEDs are in excellent agreement with the predictions of a full pf-shell model.

Rotational bands in the odd-proton nucleus 171 Lu have been populated with the 160 Gd( 19 F, α4n) reaction. High-spin states were observed to a maximum spin of 73 2 − using the NORD-BALL array. Several new three-quasiparticle bands were observed, including one based on the π 1 2 − [541]⊗ν 7 2 + [633]⊗ν 1 2 − [521] configuration. The signature splitting of this band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. The contribution of this interaction to the increased crossing frequency observed for the alignment of i 13 2 neutrons in the π 1 2 − [541] band is considered. Strong E1 transitions from high-spin levels in the π 1 2 + [411] band to the π 1 2 − [541] band are observed.

The nucleus 102Pd has been studied using 148 MeV 34S ions impinging on 76Ge. The γ-rays were detected with the Nordball array and the light charged particles with a 4π charged particle detector system. Rotational bands have been extended using γ-ray yields, γγ coincidences and angular correlation information. Calculated spin diabatic surfaces were used for assigning quasiparticle configurations to the bands. The (+,0) high spin band extending to 26+ may be explained by a π( g 9 2 ) 2 ⊗ ν(“ g 7 2 ”) 2 quasiparticle configuration. The protons are predicted to align first. The negative parity bands are suggested to be built on ν (“ g 7 2 ” h 11 2 ) evolving to π( g 9 2 ) 2 ⊗ ν(“ g 7 2 ” h 11 2 ) at the highest spins.

High spin states in 105Cd have been studied using reactions 106Cd(p, pn), 106Cd(3He, 2p2n), 92Zr(16O, 3n) and 76Ge(34S, 5n). The excited levels are dominated by a negative parity band structure up to spin 47 2 − and a positive parity structure up to spin 27 2 + . The negative parity structure is based on ν h 11 2 excitations and undergoes a band crossing at h ω ≈ 0.44 MeV . This band crossing is interpreted as an alignment of a g 7 2 neutron pair. The positive parity excitations are understood as due to ν g 7 2 and ν d 5 2 configurations. The results are discussed in terms of spin diabatic surface calculations.

High-spin states in 171Re have been studied using the reaction 123Sb(52Cr, 4n)171Re. A back-bend in the i132 band of a Re nucleus has been fully delineated for the first time. A new back-bend has also been observed in the 52+[402] band and other bands have been extended to higher spin and added to the level scheme. Band crossings are interpreted using the CSM and three-band mixing calculations. These appear to show evidence for shape coexistence and configuration-dependent neutron pairing.

A candidate for chiral bands was found in Tl-198 for the first time in a mass region of oblate (or nonaxial with gamma >= 30 degrees) deformed nuclei. Two bands show very similar quasiparticle alignments, moments of inertia, and B(M1)/B(E2) ratios. They have a relative excitation energy of about 500 keV and different patterns of energy staggering. Calculations using the two-quasiparticle-plus-triaxial-rotor model with residual proton-neutron interaction included show that a triaxial deformation with gamma similar to 44 degrees agrees very well with all the experimental observations. Furthennore, considerable energy staggering for both partner bands was calculated for this pi h(9/2) circle times vi(13/2)(-1) configuration at gamma - 30 degrees, suggesting that chiral bands may have substantial energy staggering. (Less)

The neutron deficient nucleus 108Te was studied in the 54Fe(58Ni,2p2n) reaction. A detector system consisting of 4 Euroball cluster detectors, a charged-particle detector ball and a 16 element neutron multiplicity filter was used to detect the emitted particles and γ rays. A new, significantly extended level scheme was constructed on the basis of γγ-coincidence relations. Spin values for the states were determined from angular distribution ratios. The experimental results are discussed in terms of the shell model.

The low-lying levels in the odd-odd N = Z nucleus 62 Ga have been identified for the first time. These data reveal a cascade of stretched-E2 transitions based on a T =0, 1 + bandhead which decays directly to the T =1, 0 + ground state. The observed levels are interpreted in the context of theshell model, using as a basis, the pf 5/2 g 9/2 orbits with a 56 Ni core.

Tilted-axis rotation, arising from Fermi-aligned configurations, has been observed for the first time to cause backbending in an odd-proton nucleus. In 181Re, two t-bands are found to be energetically favored relative to the usual rotation-aligned s-bands, presenting an alternative form of cold nuclear rotation. Interactions between the bands are weak, and unambiguous comparisons with tilted-axis-cranking calculations can be made.

High-spin states in 185Re have been studied using the 176Yb(13C,p3n) reaction at 65 MeV. Levels up to spin (37/2) h at Ex = 4.799 MeV have been identified. Among them two levels were observed with half-lives of 6 ± 2 ns and 123 ± 23 ns.

The γ-decay of the Giant Dipole Resonance (GDR) built on excited nuclear states has been measured for the nucleus143Eu. The reaction110Pd(37Cl, 4n)143Eu at a beam energy of 165 MeV has been employed. This experiment aimed at searching the γ-decay of the GDR built on the superdeformed143Eu states, populated at high spins. High-energy γ-rays were detected in 8 large BaF2 scintillators in coincidence with discrete transitions measured with the NORDBALL array (in the configuration consisting of 17 HPGe detectors and a 2π multiplicity filter). The spectrum of high-energy γ-rays gated by low-energy transitions between states fed by the superdeformed states shows some excess of yield in the 7–10 MeV region with respect to that gated by transitions between states not populated by the superdeformed states. This excess should be due to the γ-decay of the the giant dipole oscillation along the superdeformed axis of the nucleus that is expected to have a frequency corresponding to ≈9–10 MeV (low-energy component of the GDR strength function). The measured excess, in spite of the large error bars, is found to be of the same order as predicted statistical model values.