摘要:

Recent experiments withGammasphereand theMicroballcharged‐particle detector array have led to the identification, and have enabled the detailed spectroscopic study, of highly‐deformed and superdeformed rotational bands in a number ofA∼ 40,N≈Znuclei. These rotational bands are built on multi‐particle multi‐hole excitations across theN,Z= 20 shell gap from thesdto thepfshell and, in the context of the Nilsson scheme, are associated with the shell gaps formed at large prolate deformation for particle numbersN,Z= 16, 18, 20 aspf‐shell intruder orbitals are occupied. In analogy with well‐developed rotational motion in heavy nuclei, these highly collective rotational structures involve active valence particles in two major shells for both protons and neutrons, yet theA∼ 40 bands possess the unique advantage that the valence space dimension remains small enough to be approached from a shell‐model perspective. These rotational bands thus provide an ideal opportunity for detailed comparisons between experimental data and both microscopic and macroscopic models of collective motion in nuclei. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556616

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The excitation energy, spin and parity of the yrast superdeformed band 1 in152Dy have been established. The evidence comes mainly from the measured properties of a 4011 keV single‐step transition connecting the yrast superdeformed level fed by the 693 keV transition to the 27−yrast state. Four additional, weaker, linking &ggr; rays have been placed as well. The excitation energy of the lowest superdeformed band 1 member is 10,644 keV and its spin and parity are determined to be 24+. A further nine transitions of dipole character have been identified, which connect the excited superdeformed band 6 in152Dy to the yrast SD band 1. The excitation energy of the lowest level in the excited SD band 1 is 14,239 keV. The lowest state in band 6 has been determined to be of negative parity and odd spin (29−or 31−). The measured properties of band 6 are consistent with an interpretation in terms of an octupole vibrational band. A comparison with an RPA calculation by Nakatsukasaet al.suggests that the spin of the lowest SD band 6 level is 31−. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556617

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

High‐spin states in108Cd were studied following the reaction64Ni(48Ca,4n) at a beam energy of 207 MeV. Gamma rays were detected using the Gammasphere array. Two rotational bands have been observed at very high angular momentum. Measurements of fractional Doppler shifts yielded lower limits for the quadrupole moments and showed that the observed structures are at least as deformed as the superdeformed structurese.g.in theA≈ 150 region, and possibly exceed a 2:1 axis ratio. The existence of very extended shapes has been predicted by cranked Strutinsky calculations, and recent projected shell model calculations suggest that the &pgr;i13/2hyper‐intruderorbital is occupied in these newly observed bands. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556618

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Multiple superdeformed bands in the nuclei80–83Sr,82–84Y, and83,84Zr have been studied in a backed‐target experiment using the Gammasphere and Microball detector arrays. For 15 bands in these nuclei, average transition quadrupole moments (Qt) have been measured accurately. Among those are two pairs of “isospectral” bands and the Qtvalues obtained in each case are nearly identical. The measured Qtvalues and dynamical moments of inertia place stringent conditions on configuration assignments for the bands obtained from mean field calculations. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556619

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The rotational damping width &Ggr;rot and the compound damping width &Ggr;comp are two fundamental quantities that characterize rapidly rotating compound nuclei having finite thermal excitation energy. A two‐component structure in the strength function of consecutive E2 transitions reflects the two widths, and it causes characteristic features in the double and triple gamma‐ray spectra. We discuss a new method to extract experimentally values of &Ggr;rot and &Ggr;comp. The first preliminary result of this method is presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556620

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In a mixture of three Yb nuclei, we find the rotational damping widths vary from 180 keV at 1.1 MeV &ggr;‐ray energy to 290 keV at 1.5 MeV, and theaveragecompound damping widths (or spreading widths) vary from 40 keV at 1.1 MeV &ggr;‐ray energy to 60 keV at 1.3 MeV. The simulations also suggest extensive motional narrowing. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556621

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

New structures above and below the two‐particle isomeric states in188Pb have been identified. Their properties are consistent with the presence of three minima in the nuclear potential well, associated with spherical, weakly oblate and substantial prolate deformations. The fragmented decay of the weakly populated K&pgr;= 8−, 1 &mgr;s prolate isomer also provides a means of identifying non‐yrast low‐spin structures which are otherwise inaccessible. Through this mechanism, collective bands which can be associated with the excited 0+states have been identified and E0 transitions between them inferred. Analysis of the excitation energies, branching ratios and E2/E0 decay‐width ratios through a band‐mixing model provides a test of shape differences and the separability of the wave functions at low spin. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556622

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

With the coupling of large &ggr;‐ray arrays to recoil mass spectrometers, in‐beam gamma‐ray studies can be performed on nuclei lying at the very edges of stability. We have recently performed in‐beam experiments using Gammasphere coupled to the FMA to measure excited states in proton unbound Au isotopes and neighboring Hg isotopes. These studies have allowed us to characterize the evolution of nuclear shapes as one approaches the proton drip line. In two of the isotopes studied, namely,175Au and179Hg, structures built on three distinct shapes at low excitation energy have been observed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556623

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Prompt and delayed &ggr; rays from in191,193Bi have been identified using the recoil‐decay tagging (RDT), isomer tagging, and recoil gating techniques, resulting in extensive level schemes for both nuclei. Excitation energies of the isomeric 13/2+states have been established and rotational bands based on them have been observed. The nearly spherical 9/2−ground‐state bands appear to be crossed by more deformed low‐lying structures. TRS calculations have been performed and B(M1)/B(E2) ratios have been extracted for the observed strongly‐coupled bands. In193Bi, a 3 &mgr;s isomer has been interpreted as ah9/2proton coupled to the 12+state of the192Pb core. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556624

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Several searches for new proton emitters were performed recently at ATLAS using the Argonne Fragment Mass Analyzer equipped with a Double‐Sided Si Strip Detector. Proton emitting states were observed in odd‐odd spherical nuclei164Ir and170Au.164Ir is the fourth Ir proton emitter. A proton line was associated with the highly deformed odd‐odd nucleus130Eu. The proton emitter135Tb was also observed. It is the first proton emitting Tb isotope. The estimated cross section for producing135Tb is about 2 nb. The properties of the proton emitters deduced from this work helped to understand the role of core vibrations and neutrons in proton decay. In view of the present results the full delineation of the proton drip‐line between Z=50 and Z=83 is feasible. In order to cope with small cross sections and short half lives expected for even more exotic proton emitters several modifications of the FMA implantation station were implemented. Measurements were also performed at the target position using a catcher to search for proton emitters with half lives down to 10 ns. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556625

出版商:AIP    

年代:1903

数据来源: AIP