Four previously known rotational bands in Rb-76 have been extended to moderate spins using the Gammasphere and Microball gamma ray and charged particle detector arrays and the Ca-40(Ca-40,3pn) reaction at a beam energy of 165 MeV. The properties of two of the negative-parity bands can only readily be interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model calculations if they have the same configuration in terms of the number of g(9/2) particles, but they result from different nuclear shapes (one near-oblate and the other near-prolate). These data appear to constitute a unique example of shape coexisting structures at medium spins. (C) 2011 Elsevier B.V. All rights reserved.

Two of the four known rotational bands in Rb-75 were studied via the Ca-40(Ca-40,alpha p)Rb-75 reaction at a beam energy of 165 MeV. Transitions were observed up to the maximum spin I-max of the assigned configuration in one case and one-transition short of I-max in the other. Lifetimes were determined using the residual Doppler shift attenuation method. The deduced transition quadrupole moments show a small decrease with increasing spin, but remain large at the highest spins. The results obtained are in good agreement with cranked Nilsson-Strutinsky calculations, which indicate that these rotational bands do not terminate, but remain collective at I-max.

The nucleus Kr-74 has been populated in the Ca-40(Ca-40,2p alpha)Kr-74 fusion-evaporation reaction at a beam energy of 165 MeV and studied using the Gammasphere and Microball multidetector arrays. The lifetimes for low-spin states in the ground-state and two signature-split negative-parity bands were determined using the Doppler-shift attenuation method. These results are discussed together with the lifetimes measured for the high-spin states of these bands and compared with theoretical calculations.

Lifetimes have been deduced in the intermediate/high-spin range for the three known rotational bands in Kr-73 and the T = 0 band in Rb-74 using the residual Doppler shift method. This has enabled relative transition quadrupole moments to be studied for the first time in triaxial nuclei as a function of spin. The data suggest that the additivity principle for transition quadrupole moments is violated, a result that is in disagreement with predictions from cranked Nilsson-Strutinsky and cranked relativistic mean-field theory calculations. The reasons for the discrepancy are not understood but may indicate that important correlations are missing from the models.

High-spin states in the N=Z nucleus Kr72 have been populated in the Ca40(Ca40, 2α)Kr72 fusion-evaporation reaction at a beam energy of 165 MeV using the Gammasphere array for γ-ray detection coupled to the Microball array for charged particle detection. The previously observed bands in Kr72 were extended to an excitation energy of ∼24 MeV and angular momentum of 30ℏ. Using the Doppler shift attenuation method the lifetimes of high-spin states were measured for the first time. Excellent agreement between the results of calculations within the isovector mean field theory and experiment is observed both for rotational and deformation properties. No enhancement of quadrupole deformation expected in the presence of isoscalar t=0 np pairing is observed. Current data do not show any evidence for the existence of the isoscalar np pairing.Received 23 November 2005Corrected 19 April 2007DOI:https://doi.org/10.1103/PhysRevC.75.041301©2007 American Physical Society

High-spin states in Sr-76 have been studied using Gammasphere plus Microball detector arrays. The known yrast band has been extended beyond the first band crossing, which involves the simultaneous alignment of pairs of g(9/2) protons and neutrons, to a tentative spin of 24h. The data are compared with the results of cranked relativistic mean-field (CRMF) and cranked relativistic Hartree-Bogoliubov (CRHB) calculations. The properties of the band, including the g(9/2) proton/neutron band crossing frequency and moments of inertia, are found to be well reproduced by the CRHB calculations. Furthermore, the unpaired CRMF calculations show quite good agreement with the data beyond the band crossing region, indicating that pairing is weak at these frequencies. The high spin results suggest that there is little evidence for an isoscalar (t=0) np pair field. Moreover, a systematic study of the band crossings in even-even N=Z nuclei for the first time reveals that there is no evidence to support the existence of the Coulomb antipairing effect caused by the Coulomb exchange term.

High-spin states in the N=Z nucleus Kr-72 have been populated in the Ca-40(Ca-40, 2 alpha)Kr-72 fusion-evaporation reaction at a beam energy of 165 MeV using the Gammasphere array for gamma-ray detection coupled to the Microball array for charged particle detection. The previously observed bands in Kr-72 were extended to an excitation energy of similar to 24 MeV and angular momentum of 30h. Using the Doppler shift attenuation method the lifetimes of high-spin states were measured for the first time. Excellent agreement between the results of calculations within the isovector mean field theory and experiment is observed both for rotational and deformation properties. No enhancement of quadrupole deformation expected in the presence of isoscalar t=0 np pairing is observed. Current data do not show any evidence for the existence of the isoscalar np pairing.

High-spin states in $^{76}\mathrm{Sr}$ have been studied using Gammasphere plus Microball detector arrays. The known yrast band has been extended beyond the first band crossing, which involves the simultaneous alignment of pairs of ${\mathrm{g}}_{\frac{9}{2}}$ protons and neutrons, to a tentative spin of $24\ensuremath{\hbar}$. The data are compared with the results of cranked relativistic mean-field (CRMF) and cranked relativistic Hartree-Bogoliubov (CRHB) calculations. The properties of the band, including the ${\mathrm{g}}_{\frac{9}{2}}$ proton/neutron band crossing frequency and moments of inertia, are found to be well reproduced by the CRHB calculations. Furthermore, the unpaired CRMF calculations show quite good agreement with the data beyond the band crossing region, indicating that pairing is weak at these frequencies. The high spin results suggest that there is little evidence for an isoscalar $(t=0)$ $\mathit{np}$ pair field. Moreover, a systematic study of the band crossings in even-even $N=Z$ nuclei for the first time reveals that there is no evidence to support the existence of the Coulomb antipairing effect caused by the Coulomb exchange term.

High-spin states in Kr-74(36)38 were studied using the Ca-40(Ca-40,alpha 2p)Kr-74 fusion evaporation reaction at a beam energy of 165 MeV with GAMMASPHERE and MICROBALL and at a beam energy of 185 MeV with EUROBALL and ISIS multi-detector arrays. Lifetimes of the high-spin states for the ground-state band and the favoured negative-parity band have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments show a marginal decrease as a function of spin, suggesting that the rotational bands do not terminate at the maximum spin 1(max).

High-spin states in the N=Z nucleus 72Kr have been populated in the 40Ca(40Ca, 2α)72Kr fusion–evaporation reaction at a beam energy of 165 MeV and using a thin isotopically enriched 40Ca target. The experiment, performed at Argonne National Laboratory close to Chicago, USA, employed the Gammasphere array for γ-ray detection coupled to the Microball array for charged particle detection. The previously observed bands in 72Kr were extended to a higher excitation energy of ∼24 MeV and higher angular momentum of 30ℏ. Using the Doppler-shift attenuation method, the lifetimes of high-spin states were measured for the first time in order to investigate deformation changes associated with the g9/2 proton and neutron alignments in this N=Z nucleus. An excellent agreement with theoretical calculations including only standard t=1 np pairing was observed.

High-spin states in the N = Z nucleus Kr-72 have been populated in the Ca-40(Ca-40, 2 alpha) Kr-72 fusion-evaporation reaction at a beam energy of 165MeV and using a thin isotopically enriched 40Ca target. The experiment, performed at Argonne National Laboratory close to Chicago, USA, employed the Gammasphere array for gamma-ray detection coupled to the Microball array for charged particle detection. The previously observed bands in 72Kr were extended to a higher excitation energy of similar to 24MeV and higher angular momentum of 30h. Using the Doppler-shift attenuation method, the lifetimes of high-spin states were measured for the first time in order to investigate deformation changes associated with the g(9/2) proton and neutron alignments in this N = Z nucleus. An excellent agreement with theoretical calculations including only standard t = 1 np pairing was observed.

Data from three gamma spectroscopy experiments using deep-inelastic heavy ion reactions provided new information on high-spin states in the Ca-48 core nucleus and in the N=30, Ca-50 and Sc-51 isotones. Shell model calculations restricted to neutron excitations only are shown to reproduce with good accuracy some of the experimental levels. It is demonstrated that proton excitations not accounted in these calculations are abundantly present in the observed yrast structures. High energy of the 4(+) state in Ca-50 underlines the validity of the N=32 shell closure.

High-spin states in Kr-76(36)40 have been populated in the Ca-40(Ca-40,4p)Kr-76 fusion-evaporation reaction at abeam energy of 165 MeV and studied using the Gammasphere and Microball multidetector arrays. The ground-state band and two signature-split negative parity bands of Kr-76 have been extended to similar to 30 (h) over bar. Lifetime measurements. using the Doppler-shift attenuation method show that the transition quadrupole moment of these three bands decrease as they approach their maximum-spin states. Two signatures of a new rotational structure with remarkably rigid rotational behavior have been identified. The high-spin properties of these rotational bands are analyzed within the framework of configuration-dependent cranked Nilsson-Strutinsky calculations.

Data from three gamma spectroscopy experiments using deep-inelastic heavy ion reactions provided new information on high-spin states in the neutron-rich N = 30, Ca-50 and Sc-51 isotones. Shell model calculations restricted to neutron excitations only are shown to reproduce with good accuracy some of the experimental levels. It is demonstrated that proton excitations not accounted in these calculations are abundantly present in the observed yrast structures. High energy of the 4(+) state in Ca-50 underlines the validity of the N = 32 shell closure.