摘要:

First Nuclear Resonance Fluorescence (NRF) experiments were performed at the storage ring FEL‐driven High Intensity &ggr;‐ray Source (HI&ggr;S) at the DFELL. Sharp NRF &ggr;‐lines were observed from11B,32S,88Sr, and138Ba nuclei. Azimuthal NRF intensity ratios were measured around the polarized HI&ggr;S beam. Electric character was thereby deduced for 18 dipole excitations in138Ba in the energy range between 5.5 and 6.5 MeV [1] and for two dipole excitations in88Sr at 4.742 MeV and 7.535 MeV excitation energy [2]. These initial experiments demonstrate the superior performance of the HI&ggr;S facility in making such measurements [3]. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556666

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A series of in‐beam gamma ray and conversion electron studies has been performed on the Z=100 nucleus250Fm using the204Hg(48Ca,2n)250Fm reaction at the gas‐filled recoil separator RITU of the University of Jyva¨skyla¨, Finland. The ground state rotational band has been observed up to spin 18. The rotational properties are compared to those of the Z= 102 nuclei252,254No measured earlier. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556667

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The cranked relativistic Hartree+Bogoliubov theory has been applied for a systematic study of the nuclei around254No, the heaviest nuclei for which detailed spectroscopic data are available. The deformation, rotational response, pairing correlations, quasi‐particle and other properties of these nuclei have been studied with different relativistic mean field (RMF) parametrizations. For the first time, the quasi‐particle spectra of odd deformed nuclei have been calculated in a fully self‐consistent way within the framework of the RMF theory. The energies of the spherical subshells, from which active deformed states of these nuclei emerge, are described with an accuracy better than 0.5 MeV for most of the subshells with the NL1 and NL3 parametrizations. However, for a few subshells the discrepancy reach 0.7–1.0 MeV. The implications of these results for the study of superheavy nuclei are discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556668

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Despite the fact that208Pb is probably the best example of a shell model nucleus, little is known about its high‐spin states and those of its nearest neighbours, primarily because of the experimental difficulties involved in populating neutron‐rich nuclei. The high‐spin states formed from the valence orbitals are important since they provide the building blocks from which more complex configurations can be calculated. The same orbitals are involved in particle‐octupole vibrational coupling which presumably evolves into octupole deformation in heavier nuclei. In this paper we present the results of recent measurements which have used a range of reaction techniques to access states in theN= 128 isotones,211Bi,212Po and213At. The results may contribute to the understanding of the structure of the &tgr; = 65 s isomer in212Po. The new states identified include aJ&pgr; = 492+, &tgr; = 65 &mgr;s isomer in213At which decays via an enhancedE3 transition whose strength is influenced by blocking. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556669

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

High‐spin states have been studied in the octupole‐deformed222Th nucleus using the208Pb(18O,4n) reaction. De‐excitation gamma rays were detected using the Euroball‐IV gamma‐ray spectrometer. The large background of gamma rays from prompt fission fragments, which generally hampers the spectroscopy of actinide nuclei in fusion‐evaporation reactions, has been reduced using the Euroball‐IV inner BGO ball as a sum‐energy filter. With the requirement that the summed gamma‐ray energy detected in the reaction is less than 10 MeV, the intensity of222Th gamma‐rays, relative to the prompt fission background is significantly improved. The experiment and data analysis are discussed, and preliminary spectroscopic results are presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556670

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The new neutron‐rich radioactive ion beams available from the HRIBF allow an exciting variety of measurements around the132Sn region, including Coulomb excitation, fusion‐evaporation, and neutron transfer. Experiments using these beams also provide an excellent training ground for developing techniques to be used at the future RIA facility. TheB(E2;0+→ 2+) value for first 2+excited states of neutron‐rich132,134,136Te and126,128Sn have been measured by inverse‐kinematics Coulomb excitation. TheB(E2) values obtained for132,134Te are in excellent agreement with expectations based on the systematics of heavy stable Te isotopes, while that for136Te is unexpectedly small. These results are discussed in terms of the shell model and the quasiparticle random phase approximation. Neutron transfer onto a134Te beam, from9Be and13C targets to populate single‐particle states in135Te, has also been studied. Results, and plans for future experiments with these neutron‐rich beams, are presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556671

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Neutron‐rich nuclei around A∼100 were populated as fission fragments produced by the238U(&agr;,f) fusion‐fission reaction. The deexcitation &ggr; rays were detected by Gammasphere in coincidence with the detection of both fission fragments by the Rochester 4&pgr; heavy‐ion detector array, CHICO. This technique allows Doppler‐shift corrections to be applied for the observed &ggr; rays on an event‐by‐event basis thus establishing the origin of &ggr; rays from either fission fragment. In addition, it allows observation of &ggr;‐ray transitions from states with short lifetimes and offers the opportunity to study nuclear species beyond the reach of the spontaneous fission process. With these advantages, one can extend the spectroscopic study to higher spins than those derived using the thick‐target technique, and to more neutron‐rich nuclei than those derived from spontaneous fissions. Among the new and interesting phenomena identified in this rapid shape‐changing region, the most distinct result is the evidence for a prolate‐to‐oblate shape transition occurring at116Pd, which may have important implications to our understanding of the shell structure for neutron‐rich nuclei. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556672

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

108Cd was investigated using the powerful combination of two complementary experimental techniques: &ggr;&ggr;‐spectroscopy following the &bgr;‐decay of108In and the non‐selective (&agr;,n) fusion evaporation reaction. This resulted in the observation of 120 new states and more than 580 new transitions. 30 new spin assignments and more than 80 multipole mixing ratios were derived from &ggr;&ggr;‐angular correlation analyses and eight effective lifetimes stem from a Doppler Shift Attenuation (DSA) analysis following the fusion evaporation reaction. The proton 2p‐2h excited intruder band, which is typical for near proton‐magic nuclei with a sizable imbalance between valence protons and neutrons, was established up to the 4+member including lower limits for the absoluteE2 transition strengths of interband and intraband decays. The heavily suppressed absoluteE2 transition strength out of the proposed intruder band indicates pure bands with little mixing. These findings are compared to neighboring Cd isotopes and related six quasi‐proton structures. An analysis of the multi‐phonon structures observed in108Cd and heavier Cd isotopes shows that the chain of even mass cadmium isotopes may form a transitional path between the vibrational U(5) and gamma‐unstable O(6) dynamical symmetry with108Cd closer to the gamma‐soft case. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556673

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Nuclei below theZ= 50 magic shell gap with A∼100 show a wide variety of structural phenomena. These include excellent examples of vibrational collectivity at low‐spins, which give way to more rotational‐like excitations with increasing angular momentum. In this paper we present recent results from an experiment performed at Yale to study the yrast evolution of states in98,99Mo and101,102Ru. Although the high‐spin data is consistent with predictions from rotational model theories, we propose a simple presciption to distinguish between vibrational and rotational regimes of angular momentum generation. When applied to the nuclei of interest, a clear picture emerges of how these two mechanisms of collective spin generation compete in this region. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556674

出版商:AIP    

年代:1903

数据来源: AIP