摘要:

©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361356

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

An important aspect of nuclear structure is its evolution as a function of nucleon number. This takes on greater importance with access to exotic nuclei far from stability. A synoptic view of nuclear structural evolution, incorporating several new ideas and experimental results, is given, with a focus on signatures for different types of evolutionary trajectories. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361357

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The extension of the periodic system into various new areas is investigated. Experiments for the synthesis of superheavy elements and the predictions of magic numbers are reviewed. Different channels of nuclear decay are discussed like cluster radioactivity, cold fission and cold multifragmentation, including the recent discovery of the tripple fission of252Cf.©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361358

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

To obtain the highest possible resolution in a measurement has always been one of the major challenges for experimental physicists because increased resolution generally results in progress–sometimes even unexpected progress. The extraordinary resolving power which is now available for gamma-ray spectroscopy permits the measurements of tiny Doppler effects caused by the emission of primary &ggr;-rays. The induced recoil velocity (in units of the velocity of light) can be as small as ppm, leading to correspondingly small Doppler shifts. As the &ggr;-rays are emitted in all directions, a Doppler broadening rather than a Doppler shift is observed. Details of such Doppler profiles depend on the magnitude of the original recoil velocity, the slowing down time of the recoiling nuclei in the sample and the lifetimes of the excited nuclear states that are populated subsequent to the recoil. Gamma Ray Induced Doppler broadening (GRID) measurements have given rise to applications in nuclear and condensed matter physics. On the one hand, one can obtain information about lifetimes of excited nuclear states in the pico second to femto second region. On the other hand, one can–via the study of the slowing down process –obtain information about inter-atomic potentials in the eV to 100 eV region. The latter method becomes especially precise when oriented single crystals are used as targets. Due to the regular arrangement of atoms in a single crystal the rate of slowing down in such samples depends on the direction of recoil due to blocking and/or channelling effects. Therefore the shape of the observed Doppler profiles depends directly on the orientation of the crystal with respect to the spectrometer. Fine structure appears which allows the determination of inter-atomic potentials and/or the lifetimes of excited nuclear states. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361359

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The nature of the low-lyingK=0+excitations in deformed nuclei has recently been the subject of intense discussion. Due to different competing modes to produce such excitations it is often difficult to interpret the data related to these excitations. Experimentally, due to the difficulty of populating such states and of detecting low intensity &ggr; rays, studies of these modes constitute a real challenge. Two categories of experiments will be presented: high resolution &ggr;-ray measurements with the GAMS4 spectrometer following the (n,&ggr;) reaction at ILL Grenoble(158Ge)and high efficiency &ggr;&ggr; measurements following &bgr;(&Vegr;)-decay performed at WNSL(162Dy).Evidence for phase coexistence in150Sm(GRID method) and152Sm(&ggr;&ggr; following &Vegr;-decay of152Eu) will be also presented. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361360

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

K&pgr;=0+excitations one of the most elusive structures in nuclear physics. Part of the elusiveness of the problem is due to the sparsity of lifetime data for levels ofK&pgr;=0+excitations. In this paper, we report on level lifetime measurements of severalK&pgr;=0+bands in178Hfand156Gdnuclei using the GRID technique. Our results point to a previously unobserved case of two excitedK&pgr;=0+bands connected by collective E2 transitions in178Hfand an enormously collectiveK&pgr;=0+band in156Gdconnected to two lower lyingK&pgr;=0+bands. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361361

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Isovector M1 transitions between low-lyingT=1andT=0states in odd-oddN=Znuclei are discussed. Simple analytical expressions for M1 transition strengths are given in single-j-shell approximation. The large B(M1) values for thej=l+1/2case are attributed toquasi-deuteron configurations. The B(M1) values for thej=l−1/2case are found to be small due to a cancellation of spin and orbital parts of the M1 matrix element. The experimental data on low spin states in the odd-odd nucleus54Coinvestigated with the54Fe(p,n&ggr;)54Cofusion reaction at the FN-TANDEMaccelerator in Cologne are reported. TheJ&pgr;=01+,21+,41+&hthinsp;T=1andJ&pgr;=11+,31+,T=0states are identified as predominantly&pgr;f7/2−1×&ngr;7/2−1quasi-deuteronstates. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361362

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The02+level in deformed nuclei has historically been given the label &bgr;, even though its properties vary drastically from one nucleus to another. By reviewing models from where the original term &bgr; vibration arose, and appealing to microscopic calculations, guidelines are proposed for the properties of a true &bgr; vibration. An examination of available data, includingB(E2)values,&rgr;2(E0)values, and single- and two-nucleon-transfer populations, shows that very few02+levels satisfy the criteria for a &bgr; vibration. It is suggested that pairing excitations may be playing a dominant role. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361363

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

&ggr;-spectroscopy of low-lying low-spin states of the near-spherical nucleus94Mois reported. Photon scattering experiments and &ggr;&ggr;-coincidence measurements of &ggr;-radiation following the &bgr;-decay of94Tcnuclei produced in the94Mo(p,n)reaction and following the91Zr(&agr;,n)94Moreaction were performed. We measured level energies, spin and parity quantum numbers, branching ratios, multipole mixing ratios, and lifetimes for low-spin states, which are high above yrast. The mixed-symmetry(MS)2+one-quadrupole phonon excitation and the(MS)1+and3+two-phonon states are identified from measuredM1andE2transition strengths. We observed &ggr;-transitions between MS states and theE2/M1multipole mixing ratios of theF-vector1+→21+,22+transitions were measured. The data support the two-phonon character of the1+MSstate. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361364

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The results of lifetime measurements on low-lying superdeformed (SD) states in the mass-190 region are summarized. Recoil distance Doppler-shift experiments were performed with the large gamma-ray arrays GASP and Gammasphere employing the Cologne plunger device. The results show that decay out of the SD bands is governed by a weak mixing of cold SD with hot normal deformed (ND) states. Estimates for squared ND mixing amplitudesan2and the maximum spreading width&Ggr;max↓of the SD states are presented and compared to theoretical predictions. The known linking transitions in194Hgand194Pbshow no enhanced transition strength, supporting the assumption of a statistical decay of the hot ND states. Monte Carlo calculations based on a nearest neighbor mixing approach are presented and the spin dependence of&Ggr;↓is discussed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361365

出版商:AIP    

年代:1900

数据来源: AIP