LES NOYAUX DE TRANSITION 189Ir ET 187Ir SONT-ILS TRIAXIAUX ?

Les niveaux excités des noyaux 189Ir et 187Ir ont été étudiés par réaction (α, 2nγ) sur le faisceau du cyclotron de Grenoble. Les schémas détaillés qui ont été établis mettent en évidence : 1) des états de parité positive qui s'interprètent comme appartenant aux deux bandes 3/2+ | 402 | (fondamental) et 1/2+ | 400 | mélangées par interaction de Coriolis (noyaux a symétrie axiale de déformation positive) ; 2) une bande découplée construite sur un état 9/2- (h 9/2) décrite de manière équivalente par un modèle à symétrie axiale et déformation positive ou par un modèle a particule-plus-rotor asymétrique ; 3) une structure complexe pour les niveaux de parité négative associés à l'isomère 11/2- (h 11/2). Ce système est correctement prédit par le modèle à rotor asymétrique

Lifetimes of high spin states in Ir181 and Os180

The Nd150(35Cl,4n)181Ir and Nd150(34S,4n)180Os reactions have been used to study the lifetimes of high-spin states in Ir181 and Os180 using the recoil-distance technique. The lifetimes of four states in Ir181 and three yrast states in Os180 have been determined. The mean weighted values of quadrupole moments deduced for the measured rotational transitions between yrast states in Ir181 and Os180, Q0=(6.0±0.2) e b and Q0=(6.1±0.4) e b, respectively, are equal within experimental errors

Magnetic and intruder rotational bands in (113)In

©2005 American Physical SocietyExcited states in ¹¹³In were populated via the reactions ¹⁰⁰Mo(¹⁸O,p4n)¹¹³In and ¹¹⁰Pd(7Li,4n)¹¹³In. The two known ΔJ = 2 intruder bands, based on the πg7/2 ⊗ d5/2 and πh11/2 orbitals, have been extended by 8¯h to spins (49/2+)¯h and (55/2−)¯h, respectively. The previous finding of three sequences of ΔJ = 1 γ -ray transitions has been confirmed. A self-consistent cranked shell-model calculation gives a good description of the contrasting alignment patterns of the two ΔJ = 2 intruder bands. The intruder bands, the known sequences ofM1 transitions, and spherical levels together represent a coexistence of three different excitation modes in this nucleus.S. Naguleswaran, R. S. Chakrawarthy, U. Garg, K. L. Lamkin, G. Smith, J. C. Walpe, A. Galindo-Uribarri, V. P. Janzen, D. C. Radford, R. Kaczarowski, D. B. Fossan, D. R. Lafosse, P. Vaska, Ch. Droste, T. Morek, S. Pilotte, J. DeGraaf, T. Drake, and R. Wys

Backbending in the 1 2-[541] band in 181 Ir

A backbending has been observed in the 1 2-[541] band in the odd-proton nucleus 181Ir at h{stroke}ω ∼ 0.3 MeV, with Δix ∼ 6.5h {combining short solidus overlay}, in contrast with only an upbend observed near this frequency in the "core" nucleus 180Os. The nature of this backbend is explored in the framework of the cranked Hartree-Fock-Boguliubov approximation

Level structures of 96,97,98Ru at high angular momentum

The high-spin level structures of 96,97,98Ru (Z544) have been investigated using the 65Cu(36S, pxn)96,97,98Ru (x54,3,2) reactions. About 130 new transitions have been observed and unambiguously placed in the decay schemes of these nuclei. The level schemes have been extended up to spin J'22– 34\, and excitation energies Ex'20224 MeV. Spherical shell model calculations have been performed and theoretical level energies compared with experimental values. Calculations using 88Sr as the core give a reasonable agreement for the observed energy levels up to J16\), possibly manifesting vibrational behavior

Level structure of 94,95,96Tc at high spins and shell-model calculations

High-spin states in the 94,95,96Tc (N = 51, 52, and 53) nuclei have been investigated using the 65Cu+H36S reaction at a beam energy of 142 MeV. More than 60 new transitions have been identified and placed in their level schemes, which now extend up to spin J ≈ 22ℏ and excitation energies Ex ≈ 12 MeV. Spherical shell-model calculations have been performed using different model spaces. A restricted model space, using 88Sr as the core and the π(p 1/2,g9/2) ν(d5/2,s1/2) valence orbitals, reproduces the experimental excitation energies up to J ≈ 14ℏ. The higher-angular-momentum states are dominated by the excitation of a g9/2 neutron across the N = 50 magic core, as indicated by large-basis shell model calculations

Nuclear structure of 94,95Mo at high spins

The high-spin level structures of 94,95Mo (N552,53) have been investigated via the 65Cu(36S, a p2n)94Mo and 65Cu(36S, a pn)95Mo reactions at 142 MeV. The level schemes have been extended up to spin J'19\ and excitation energies Ex'12 MeV. Spherical shell-model calculations have been performed and compared with the experimental energy levels. The level structure of 94Mo exhibits a single-particle nature and the higher-angular-momentum states are dominated by the excitation of a g9/2 neutron across the N550 shell gap. The level sequences observed in 95Mo have been interpreted on the basis of the spherical shell model and weak coupling of a d5/2 or a g7/2 neutron to the 94Mo core

High-spin states in 97,98Rh

High-spin states in 97,98Rh (Z545) were populated via the 65Cu( 36S,xn)97,98Rh (x54,3) fusion-evaporation reactions. More than 40 additional transitions have been identified and placed in the decay schemes of these nuclei. The level scheme of 97Rh has been extended up to tentative spins of Jp 539/21,37/22, and the placement of some of the previously known transitions has been revised. The level structure of 97Rh indicates a single-particle nature and the observed levels are reproduced well by spherical shell-model calculations. The level scheme of 98Rh has been extended up to spins J;20\ and up to an excitation energy of ;10 MeV. The low-spin structure of 98Rh (J<10\), appears to indicate also a singleparticle structure, as supported by the stretched coupling scheme @ 97Rh(J8)^n (d5/2)598Rh (J)#

Recoil-distance lifetime measurements in 96,97,98Ru: Search for possible onset of collectivity at N≥52

Lifetimes of high-spin states in the N =52-54 Ru nuclei have been investigated via the 65Cu(36S,pyn)96,97,98Ru (y = 4,3,2) reactions using the recoil-distance Doppler-shift technique. The data were collected in coincidence mode. Lifetimes have been extracted for both the positive-and the negative-parity states in 96Ru and 98Ru and for the positive-parity states in 97Ru. The levels studied have lifetimes in the range 2-31 ps. The observed reduced transition probabilities B(E2) and B(M1) are compared with the predictions of the shell model. Theoretical implications of these results are discussed