Loss of collectivity along the yrast line in 158Er

Lifetimes of yrast states from spin 14 through 40 have been measured in ¹⁵⁸Er. The Doppler-shift recoil-distance method was used in conjunction with the multi-Ge detector array HERA, and γγ coincidences were analyzed. The collectivity of the nucleus drops from 200 W.u. to 110 W.u. in the region of the second backbend. By spin 38 it has decreased further to 25 W.u., consistent with a band termination.     

Doorway states in the gamma decay-out of the yrast superdeformed band in 59Cu

The decay-out process of the yrast superdeformed band in 59Cu has been investigated. The firm determination of spin, parity, excitation energy, and configuration of the states involved in this process constitutes a unique situation for a detailed understanding of the decay-out mechanism. A theoretical model is introduced that includes a residual interaction and tunneling matrix element between bands, calculated in the configuration-dependent cranked Nilsson-Strutinsky model. This interaction causes the decay to occur via a small number of observed doorway states.     

Negative-parity bands in the 88-neutron nuclei153Tb and155Ho

Bands of negative-parity levels have been observed in in-beam studies of¹⁵³Tb and¹⁵⁵Ho. The data are qualitatively accounted for in the rotation-alignment model as decoupled bands based on the h_11/2 proton orbital. Nuclear Reactions:¹⁵³Eu(α, 4nγ)¹⁵³Tb,E=45–55 MeV;¹⁵⁰Sm(¹⁰B, 5nγ)¹⁵⁵Ho,E=60–70 MeV; measuredE _γ,I _γ (0), γ ? γ coinc.,E _e, I _e ^K ,¹⁵³Tb and¹⁵⁵Ho deduced levels,J, π. Ge(Li) and Si(Li) detectors. Enriched targets.     

Second backbending in the yrast line of 156Er

High spin yrast states of ¹⁵⁶Er were investigated using the reactions ¹⁴¹Pr(¹⁹F,4nγ) and ¹²³Sb(³⁷Cl, 4nγ), the latter in connection with a sum-crystal. In addition to the backbending at $\text{I = 12}\text{h}\text{?}$, a second one is found at $\text{I = 26}\text{h}\text{?}\text{;}$ and the yrast band is extended up to $\text{I = 32}\text{h}\text{?}\text{;}$. These results are interpreted in terms of a Hartree-Fock-Bogolyubov Cranking (HFBC) method. It is demonstrated that for deformations in the vicinity of the Strutinsky equilibrium deformation, both a 2qp proton band crossing the yrast band or a 4qp neutron band crossing the yrast band can cause strong secondary backbending.     

Microstructure of excited nuclear states in the vicinity of an yrast line

The microscopic model describing the wobbling motion in fast rotating nuclei is presented and the connection of the parameters describing it with the Coriolis effects at low spins is discussed.     

Analytical method for yrast line states in the interacting two—component Bose—Einstein condensate

The yrast spectrum for the harmonically trapped two-component Bose-Einstein condensate (BEC),omitting the difference between the two components,has been studied using an analytical method.The energy eigenstates and eigenvalues for L=0,1,2,3 are given,We illustrate that there are different eigenstate behaviours between the even L and odd L cases for the two-component BEC in two dimensions.Except for symmetric states,there are antisymmetric states for the permutation of the two components,which cannot reduce to those in a single condensate case when the value of L is odd.     

Microscopical structure of the states of deformed nuclei in the neighborhood of the yrast line

A simple model is derived which allows one to study the structure of the nuclear states in the neighborhood of the “yrast” band. In the present scheme the precession motion plays a role of one of the normal modes of oscillations. (The structure of the dispersion equation for this mode corresponds to the well known classical formula.) Vibrational states associated with quadrupole oscillations of the nuclear shape are determined from a general equation. At slow rotation this equation breaks up into the known equations for β-, Δ- and γ-vibrations and non-collectivized K^π = 1⁺ excitations.     

Single particle nature of the yrast line at high angular momentum in 152Dy

Linear polarization and Doppler shift recoil-distance decay curves for γ-ray transitions deexciting very high spin yrast states up to spin 36? in ¹⁵²Dy were measured with a delayed-promt γ-γ coincidence technique via the reactions ¹²²Sn (³⁴S, 4n) and ¹²⁴Sn(³²S, 4n), at 150 MeV incident beam energy. The deduced experimental transition probabilities are consistent with those obtained for non-rotational nuclei indicating that the yrast angular momentum originates mainly from the alignment of individual particle spins.     

Multiparticle continuum in the excitation spectrum of the compound CsNiCl

Recent neutron scattering experiments on CsNiCl₃ reveal some features that are not well described by the standard nonlinear σ model, nor by numerical simulations, for isolated S = 1 spin chains. In particular, in real systems at the antiferromagnetic point of the Brillouin zone, the intensity of the continuum of multiparticle excitations, at T = 6 K, is about 5 times greater than predicted. Also, the spin gap is higher and the correlation length is smaller than predicted. We propose a theoretical scenario where the interchain interaction is approximated by an effective staggered magnetic field, and that yields a correct prediction for the observed quantities. Received 2 October 2002 / Received in final form 19 March 2003 Published online 7 May 2003     

Possible candidates for discrete gamma rays linking superdeformed and yrast states in an odd nucleus:193Pb

The francium isotopes^200–202Fr were produced in the reaction³⁵Cl+¹⁷⁰Yb using bombarding energies of 4.9–5.3 MeV/nucleon. Fusion products were separated in-flight from the primary beam using a gas-filled recoil separator. An alpha line with the alpha particle energy and half-life of (7468±9) keV and (19 ₋₆ ⁺¹³ ) ms, respectively, was assigned to²⁰⁰Fr. Previously reported decay properties of^201,202Fr were confirmed. Communicated by V. Metag     

Nuclear quantum Monte Carlo: Expanding into the continuum

I discuss calculations of nuclear properties using the variational Monte-Carlo (VMC) and Green’s function Monte-Carlo (GFMC) methods in combination with realistic two- and three-nucleon interactions. Work to date has emphasized energies of bound and narrow states, and the results agree well with measured masses and energies. We are now directing more effort toward other nuclear properties, including weak decay rates and nuclear charge radii. The main new direction is the computation of low-energy scattering and reaction properties. We have incorporated R-matrix-like boundary conditions into GFMC calculations, and our first calculation of this kind has yielded phase shifts for neutron scattering on ⁴He up to a few MeV. We find strong dependence of the results on the three-nucleon interaction used.     

Structure of the yrast line in 42Ca up to the alpha-particle pinch-off

The yrast line of ⁴²Ca has been investigated with the reaction ${}^{27}\text{Al}\text{(}{}^{19}\text{F}\text{, 2}\text{p}\text{2}\text{n}\text{γ)}{}^{42}\text{Ca at}\text{E}{}_{\mathrm{<mtext>lab</mtext>}}\text{=47–108}\text{MeV}$ by means of an anti-Compton γ-spectrometer. The particular feeding and structure of the yrast line in ⁴²Ca up to J=14 is understood by weak-coupling calculations.     

Multi-quasiparticle states in 179Ta and structural changes in the yrast line of the odd tantalum isotopes

High-spin states in ¹⁷⁹Ta have been studied by a variety of γ-ray spectroscopic techniques following the ¹⁷⁶Yb(⁷Li,4n) reaction. The new results independently confirm and extend the one-, three- and five- quasiparticle bands proposed previously. The more comprehensive results obtained allow firm spin assignments to be made and also the identification of rotational bands associated with the higher seniority intrinsic states. Configuration assignments follow from analysis of these rotational band properties. To explain changes in the yrast line across the chain of isotopes from ¹⁷³Ta to ¹⁷⁹Ta, multi-quasiparticle calculations have been performed and compared with experiment. The calculations, which treat pairing correlations using the Lipkin-Nogami approach and include blocking, incorporate single-particle energies adjusted to reproduce the observed one-quasiparticle bandheads. Properties specific to ¹⁷⁹Ta include evidence for configuration mixing in the $\text{21}\text{2}{}^{\mathrm{-}}$ isomer configuration. Its decay is one of several anomalously fast K-hindered transitions observed and discussed in terms of configuration changes and other mechanisms.     

Extending the nuclear chart by continuum: From oxygen to titanium

Nuclear masses ranging from O to Ti isotopes are systematically investigated with relativistic continuum Hartree-Bogoliubov (RCHB) theory, which can provide a proper treatment of pairing correlations in the presence of the continuum. From O to Ti isotopes, there are 402 nuclei predicted to be bound by the density functional PC-PK1. For the 234 nuclei with mass measured, the root mean square (rms) deviation is 2.23 MeV. It is found that the proton drip-lines predicted with various mass models are roughly the same and basically agree with the observation. The neutron drip-lines predicted, however, are quite different. Due to the continuum couplings, the neutron drip-line nuclei predicted are extended further neutron-rich than other mass models. By comparison with finite-range droplet model (FRDM), the neutron drip-line nucleus predicted by RCHB theory has respectively 2(O), 10(Ne), 10(Na), 6(Mg), 8(Al), 6(Si), 8(P), 6(S), 14(K), 10(Ca), 10(Sc), and 12(Ti) more neutrons.     

Feeding times of high-spin states in 152, 154Dy: Probes of nuclear structure above the yrast line

Measurements of feeding times of high-spin yrast states up to spin 30 ? in ¹⁵⁴Dy and 36 ? in ¹⁵² Dy were utilized to obtain information about possible spin-dependent shape changes. The reactions ²⁵Mg(¹³⁴Xe, 5n), ¹²⁴Sn(³⁴S, 4n) and ²⁵Mg(¹³²Xe, 5n), ¹²²Sn(³⁴S, 4n) were used to populate the high-spin states in ¹⁵⁴Dy and ¹⁵²Dy, respectively. Feeding times as well as lifetimes were determined with the recoil-distance technique. In ¹⁵²Dy only long feeding times (? 10 ps) could be identified, indicating that the aligned-particle yrast states are fed through configurations of similar character, with little direct population from collective cascades in the continuum region. In ¹⁵⁴Dy discrete states with I ? 30 ? have lifetimes which are characteristically collective, whereas the preyrast cascades exhibit both fast (?1 ps) and slow (～10 ps) feeding components. The latter imply a change with increasing spin from collective to aligned-particle character, probably associated with a prolate to oblate shape transition.