摘要:

Recent in‐beam &ggr;‐spectroscopic and &bgr;‐decay experiments as well as inelastic scattering studies reveal the level structure of96Zr, located at the simultaneous closure of the Z=40 and N=56 subshells, and gave an unambiguous proof of its magic character as well as of the presence of shape coexistence. These properties are reviewed in the present paper. Good agreement with preliminary results from particle‐hole RPA calculations is also reported. The recently discovered large octupole vibrational collectivity and the status of the search for two‐phonon octupole and quadrupole‐octupole states are discussed as well.

ISSN:0094-243X    

DOI:10.1063/1.41270

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High resolution Nuclear Resonance Fluorescence (NRF) experiments have been carried out to study low lying dipole excitations in rare earth nuclei. In particular, we identified the so called M1 scissors mode near 3 MeV excitation energy. At the same time we found some E1 transitions with strengths up to several mWu. The inspection of the measured decay branching ratios suggests K‐mixing for a few states while giving overall evidence for a good K‐quantum number at 3 MeV.

ISSN:0094-243X    

DOI:10.1063/1.41271

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It is shown that the effective ‘‘perturbed’’ HamiltonianHassociated with the S matrix of a system of two interacting resonances, which has one strong open reaction channel only and which is timereversal invariant, can be decomposed in a natural way into a diagonal ‘‘unperturbed’’ effective HamiltonianH0andV=H−H0. The complex energies of the ‘‘perturbed’’ system exhibit energy repulsion and width attraction as compared to the energies of the ‘‘unperturbed’’ system. This result is the direct generalization of the level repulsion theorem for the bound state case. An example in8Be is given.

ISSN:0094-243X    

DOI:10.1063/1.41272

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thermal neutron capture reaction on Ba isotopes have been studied. New levels with negative parity are introduced in odd Ba nuclei. They are interpreted in terms of neutron hole state 1h11/2coupled with even‐even core.

ISSN:0094-243X    

DOI:10.1063/1.41273

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.4755934

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The (nth,&ggr;) reaction has been measured at the ILL on the target nuclei163Dy and164Dy using the Ge pair spectrometer PN4 and the bent crystal spectrometers GAMS. Conversion electrons have been measured using the &bgr;‐spectrometer BILL, and coincident &ggr;‐rays were recorded at the end position of the neutron guide H22. Measurements in different neutron fluxes and the observation of the time dependence of the neutron capture process allowed to assign transitions in166Dy unambiguously. The multipolarities obtained from the measurement of conversion electrons were used to improve spin and parity assignments for levels in164–166Dy.

ISSN:0094-243X    

DOI:10.1063/1.41274

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The structure of the odd‐odd192Ir nucleus presents an interesting and challenging problem for both experimentalists and theorists. As a result of the common efforts of nine laboratories, it is possible, for the first time, to propose an extended scheme with 34 levels. The experiments included observation of &ggr;‐ray transitions and of conversion electrons emitted after thermal and resonance neutron capture, of direct (d,p) and (d,t) neutron transfer reactions and of the angular distribution of &ggr;‐rays from aligned192Ir nuclei. The results are interpreted in the framework of the rotor‐plus‐particle and IBFFM models. The nuclear states appear to be strongly mixed. The complex and interesting ground‐state configuration is discussed.

ISSN:0094-243X    

DOI:10.1063/1.41275

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A &ggr;&ggr;‐delayed and prompt coincidence experiment on transitions following thermal‐neutron capture by191Ir was performed using a semiconductor and scintillation detectors. The isomeric character of four transitions was established. The half‐life was deduced for the following excited states of192Ir: 66.8 keV 14.6(44) ns; 84.3 keV, 1.9(4) ns; 104.7 keV, 17(3) ns; 193.5 keV, 2.7(6) ns. The 118.8 keV level has the half‐life T1/2≳15 ns. Using these results and data on prompt coincidences a fragment of192Ir level scheme is proposed.

ISSN:0094-243X    

DOI:10.1063/1.41276

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Single‐nucleon transfer reactions have been used to study odd‐odd iridium isotopes. Angular distributions of the191,193Ir(d,t)190,192Ir reactions with 18 MeV deuterons were measured with a typical resolution of 5 keV (FWHM). Angular distributions for the191,193Ir(d,p)192,194Ir reactions, and spectra at several angles for the189Os(&agr;,t)190Ir,189Os(3He,d)190Ir and195Pt(p,&agr;)192Ir reactions were also measured. Spectroscopic strengths from the193Ir(d,t)192Ir data support previous rotor‐plus‐particle interpretations for some192Ir levels, but the 66 keV level is not readily explained by the models. In190Ir, the large number of levels populated in both the single‐neutron transfer and single‐proton transfer reactions implies appreciable mixing of the configurations.

ISSN:0094-243X    

DOI:10.1063/1.41277

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The applicability of sum‐coincidence measurements of two‐step cascade &ggr;‐ray spectra to the determination of photon strength functions at intermediate &ggr;‐ray energies (3 or 4 MeV) is discussed. An experiment based on thermal neutron capture in Nd was undertaken at the Brookhaven National Laboratory High Flux Beam Reactor (BNL HFBR) to test this model. To understand the role of various uncertainties in similar experiments a series of model calculations was performed. We present an analysis of our experimental data which demonstrates the high sensitivity of the method to E1 and M1 photon strength functions. Our experimental data are in sharp contradiction to those expected from an E1 photon strength distributed according to the classical Lorentzian form with an energy invariant damping width. An alternative distribution of Kadmenskij et al., which violates Brink’s Hypothesis, is strongly preferred.

ISSN:0094-243X    

DOI:10.1063/1.41278

出版商:AIP    

年代:1991

数据来源: AIP