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AbstractAbstract
[en] Average lifetimes and multipolarities of unresolved transitions deexciting very high spin states of the light Rare Earth nuclei (N approximately 86) have been determined by a measure of Doppler shift attenuation and their anisotropy. The spin selection is provided by the total energy spectrometer technique; great care was taken of the existence of many long lived isomeric states in the studied nuclei. The N approximately 86 nuclei have been formed in the 84Kr(340 MeV) + 74Ge → 158Er* reactions using the 84Kr beam of the Orsay ALICE facilities and targets of 74Ge built at the PARIS Isotope separator of the CSNSM. NaI γ spectra have been thoroughly cleared of the discrete lines contribution through a carefull subtraction procedure synthetising NaI spectra from the Ge ones. At very high spin the continuum γ rays feed two well separated bumps with Esub(γ) approximately .65 MeV and Esub(γ) approximately 1.3 MeV. The 1.3 MeV transitions appear at I > 30 h and their energy does not vary with the increasing spin like expected in the rotational case of the well deformed nuclei; they are strongly collectively enhanced with B(E2) > 130 W.u. Below 1 MeV the anisotropy of transitions is R approximately 0.7, indicating their stretched dipole nature. Recent calculations of nuclear shape deformation (following Strutinsky shell correction method) reproduce the two bumps shape of the experimental spectra and the origin of the excitation is explained in terms of nuclear vibration (γ-vibration, wobbling motion)
[fr]
La duree de vie et la multipolarite des transitions du continuum γ des noyaux de terres rares transitionnels (voisins de 154Er: N approximately 86) formes a tres haut spin par reaction entre ions lourds ont ete etudiees par la mesure de l'attenuation de leur decalage Doppler et de leur anisotropie. La selection des niveaux, selon leur spin, utilisant la technique de spectrometrie d'energie totale a ete realisee en tenant compte de l'existence de nombreux isomeres de longue duree de vie dans les noyaux etudies. Ces noyaux N approximativement 86 ont ete formes par reaction de 84Kr (340 MeV) accelere par ALICE (Orsay) sur des cibles de 74Ge fabriquees au separateur d'isotopes PARIS (CSNSM-Orsay). Les spectres NaI de transitions γ ont ete meticuleusement debarrasses de la contribution des raies discretes par une procedure utilisant la synthese de spectres NaI fictifs a partir des spectres Ge. A tres haut spin, les transitions du continuum γ alimentent deux bosses d'energie .65 MeV et 1.3 MeV. Les transitions de 1.3 MeV apparaissent pour I > 30 h et leur energie ne varie pas comme dans le cas rotationnel des noyaux bien deformes; elles sont de nature collective tres accelerees avec B(E2) > 130 u.W. En dessous de 1 MeV l'anisotropie des transitions est R approximativement 0.7 indiquant leur caractere dipolaire etire. Les calculs recents de deformation nucleaire (correction de couche de Strutinsky) reproduisent remarquablement la forme en deux bosses des spectres experimentaux et l'origine de l'excitation est vraisemblablement la vibration du noyau (vibration γ - mouvement de wobbling)Original Title
Etude a tres haut spin des noyaux d'Erbium transitionnels (N=86). Mise en evidence de transitions dipolaires et mesures de vies moyennes dans le continuum
Primary Subject
Secondary Subject
Source
1984; 116 p; These (3e Cycle).
Record Type
Report
Literature Type
Thesis/Dissertation
Report Number
Country of publication
ANISOTROPY, COMPOUND-NUCLEUS REACTIONS, DEFORMED NUCLEI, DSA METHOD, DYSPROSIUM, E1-TRANSITIONS, E2-TRANSITIONS, ERBIUM 153, ERBIUM 154, ERBIUM 155, ERBIUM 156, GAMMA SPECTROSCOPY, GERMANIUM 76 TARGET, HIGH SPIN STATES, HOLMIUM, ISOMERIC NUCLEI, KRYPTON 86 REACTIONS, LIFETIME, MEV RANGE 100-1000, MULTIPOLARITY, NUCLEAR DEFORMATION, STRUTINSKY THEORY
BETA DECAY RADIOISOTOPES, COUNTING TECHNIQUES, DEFORMATION, ELECTRON CAPTURE RADIOISOTOPES, ELEMENTS, ENERGY LEVELS, ENERGY RANGE, ENERGY-LEVEL TRANSITIONS, ERBIUM ISOTOPES, EVEN-EVEN NUCLEI, EVEN-ODD NUCLEI, HEAVY ION REACTIONS, INTERMEDIATE MASS NUCLEI, ISOTOPES, METALS, MEV RANGE, MULTIPOLE TRANSITIONS, NUCLEAR REACTIONS, NUCLEI, RADIOISOTOPES, RARE EARTH NUCLEI, RARE EARTHS, SPECTROSCOPY, TARGETS
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