Yrast Excitations Research Articles

Polaron-Depleton Transition in the Yrast Excitations of a One-Dimensional Bose Gas with a Mobile Impurity

We present exact numerical data for the lowest-energy momentum eigenstates (yrast states) of a repulsive spin impurity in a one-dimensional Bose gas using full configuration interaction quantum Monte Carlo (FCIQMC). As a stochastic extension of exact diagonalization, it is well suited for the study of yrast states of a lattice-renormalized model for a quantum gas. Yrast states carry valuable information about the dynamic properties of slow-moving mobile impurities immersed in a many-body system. Based on the energies and the first and second-order correlation functions of yrast states, we identify different dynamical regimes and the transitions between them: The polaron regime, where the impurity’s motion is affected by the Bose gas through a renormalized effective mass; a regime of a gray soliton that is weakly correlated with a stationary impurity, and the depleton regime, where the impurity occupies a dark or gray soliton. Extracting the depleton effective mass reveals a super heavy regime where the magnitude of the (negative) depleton mass exceeds the mass of the finite Bose gas.

Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure

Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure

Dark-soliton-like excitations in the Yang–Gaudin gas of attractively interacting fermions

Yrast states are the lowest energy states at given non-zero momentum and provide a natural extension of the concept of dark solitons to strongly interacting one-dimensional quantum gases. Here we study the yrast states of the balanced spin- Fermi gas with attractive delta-function interactions in one-dimension with the exactly solvable Yang–Gaudin model. The corresponding Bethe-ansatz equations are solved for finite particle number and in the thermodynamic limit. Properties corresponding to the soliton-like nature of the yrast excitations are calculated including the missing particle number, phase step, and inertial and physical masses. The inertial to physical mass ratio, which is related to the frequency of oscillations in a trapped gas, is found to be unity in the limits of strong and weak attraction and falls to in the crossover regime. This result is contrasted by one-dimensional mean field theory, which predicts a divergent mass ratio in the weakly attractive limit. By means of an exact mapping our results also predict the existence and properties of dark-soliton-like excitations in the super Tonks–Girardeau gas. The prospects for experimental observations are briefly discussed.

Near-yrast Excitations in Nucleus $^{83\mskip -\thinmuskip }$As: Tracing the Deformation in the $^{78}$Ni Region

Medium-spin, yrast excitations in nucleus 83As have been studied in neutron-induced fission of 235U. The experiment took place at the Institut Laue-Langevin in Grenoble where gamma rays were registered using the EXILL detector array. Recently, we proposed new tentative (9=2+) spin assignment for 2777 keV level in 83As, which is now discussed in the context of deformation showing up in 78Ni region.

First observation of excited states in87Se: Collectivity andj−1anomaly atN=53

The ${}^{87}$Se nucleus has been studied via prompt $\ensuremath{\gamma}$-ray spectroscopy using the Eurogam2 Ge array to measure $\ensuremath{\gamma}$ rays following fission of ${}^{248}$Cm. Excited levels in ${}^{87}$Se have been observed for the first time. The yrast excitation scheme in this nucleus is similar to the excitations schemes of its $N=53$ neighbors and fits the energy systematics, indicating $j\ensuremath{-}1$ anomaly below $Z=38$. Large-scale shell-model calculations reproduce in detail yrast excitations in ${}^{87}$Se and other $N=53$ isotones. The $j\ensuremath{-}1$ anomaly is explained as due to the enhancement of collectivity towards the proton midshell. The coexistence of collective and single-particle excitations is predicted in ${}^{87}$Se.

Nature of yrast excitations near N=40: Level structure of 67 Ni

Nature of yrast excitations near N=40: Level structure of 67 Ni

First observation of medium-spin excitations in the 138Cs nucleus

Medium-spin, yrast excitations in the 138Cs nucleus, populated in the spontaneous fission of 248Cm, were observed for the first time. 138Cs was studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. The newly observed yrast cascade, built on the known 6- isomer at 80 keV, was successfully described by shell model calculations. Analogously to the 136I isotone, the 6- isomer in 138Cs has the $\ensuremath{(\pi g_{7/2} ^4 d_{5/2} \nu f_{7/2})_{6^-}}$ dominating configuration and the 7- excitation, located 175 keV above, corresponds to the $\ensuremath{(\pi g_{7/2} ^3 d_{5/2}^2 \nu f_{7/2})_{7^-}}$ as dominating configuration. Similarly as in 136I, changing the position of the d 5/2 proton orbital improves the reproduction of the data. However, in 138Cs the energy of this orbital should be increased compared to its energy in 133Sb, to get the best description, in contrast to 136I and 135Sb, where it had to be decreased. The best reproduction of excitation energies in 138Cs is obtained assuming that the πd 5/2 orbital in 138Cs is located about 100 keV higher than in 133Sb. These observations suggest that the lowering of the d 5/2 s.p. energy in 135Sb is not a physical effect due to the appearance of a neutron skin, as proposed by other authors, but rather an artifact due to some deficiency of the input data used in the shell model calculations in the region of the doubly magic 132Sn core.

Development of shell closures at N=32, 34. II. Lowest yrast excitations in even-even Ti isotopes from deep-inelastic heavy-ion collisions

Development of shell closures at N=32, 34. II. Lowest yrast excitations in even-even Ti isotopes from deep-inelastic heavy-ion collisions

Two-quasiparticle bands in neutron-rich nuclei

The large multi-detector arrays such as EUROBALL and GAMMASPHERE have made possible the study of the spectroscopy of neutron-rich nuclei through the observation of discrete, prompt $\gamma$ -rays emitted following fission. Most of the information obtained has concerned yrast states and collective excitations. In the present work, a search has been made for excited bands based upon two-quasiparticle intrinsic structures. Such bands have been found in several even-even nuclei from 96Sr to 112Pd. Careful analysis of triple-coincidence spectra has been performed in order to determine branching ratios within the bands. These branching ratios are then used to establish the magnetic properties of the intrinsic structure, permitting, in most cases, the determination of which Nilsson orbits (and whether they are neutron or proton states) are contributing to the excitation. Some example results from this search are presented.

First measurements of yrast excitations in 137I and the missing 12+ isomer in 136Te

The 137I nucleus, populated in the spontaneous fission of 248Cm has been studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. Medium-spin yrast excitations in 137I were observed for the first time. The experimental level scheme is compared to the shell model calculation with modified Kuo-Herling interaction. The theoretical predictions differ significantly from the experimental results, indicating that the excitation pattern in 137I deviates significantly from the shell model scheme.

Few particle excitations ofN=83isotones134Sband135Tefrom248Cmfission

Gamma-ray cascades in the two- and three-valence-particle nuclei ${}^{134}\mathrm{Sb}$ and ${}^{135}\mathrm{Te}$ have been studied with Gammasphere using a ${}^{248}\mathrm{Cm}$ spontaneous fission source. Isotopic assignments were based in part on coincidences with \ensuremath{\gamma} rays from complementary Rh and Ru fission partners. The ${}^{134}\mathrm{Sb}$ and ${}^{135}\mathrm{Te}$ level schemes have been considerably extended, with placement of many new high-energy \ensuremath{\gamma} rays; delayed \ensuremath{\gamma}-ray coincidences observed across a 0.51-\ensuremath{\mu}s yrast isomer in ${}^{135}\mathrm{Te}$ were especially fruitful. The yrast level spectra of both nuclei are interpreted using empirical nucleon-nucleon interactions and compared with the known yrast excitations of their counterparts ${}^{210}\mathrm{Bi}$ and ${}^{211}\mathrm{Po}.$

Yrast excitations in N = 81 nuclei 132Sb and 133Te from 248Cm fission

Yrast excitations in N = 81 nuclei 132Sb and 133Te from 248Cm fission

First observation of excited states in137Teand the extent of octupole instability in the lanthanides

Excited states in ${}^{137}\mathrm{Te},$ populated in spontaneous fission of ${}^{248}\mathrm{Cm},$ were studied by means of prompt-$\ensuremath{\gamma}$ spectroscopy, using the EUROGAM2 multidetector array. This is the first observation of excited states in ${}^{137}\mathrm{Te}.$ The yrast excitations of ${}^{137}\mathrm{Te}$ are due to the three valence neutrons, occupying the $\ensuremath{\nu}{f}_{7/2}$ and $\ensuremath{\nu}{h}_{9/2}$ orbitals, similarly as observed in its heavier $N=85$ isotones. Systematic comparison of excited levels in the $N=85$ isotones shows inconsistencies in spin and parity assignments in ${}^{139}\mathrm{Xe}$ and ${}^{141}\mathrm{Ba}$ nuclei. The new data for ${}^{137}\mathrm{Te}$ do not confirm earlier suggestions that octupole correlations increase in the $N=85$ isotones, close to the $Z=50$ closed shell.

Five-valence-protonN=82isotone137Cs

Yrast excitations in the N=82 isotone {sup 137}Cs have been identified for the first time in thick-target {gamma}-ray coincidence measurements for the system {sup 232}Th+{sup 136}Xe using the Gammasphere array. The {sup 137}Cs nuclei were produced in deep inelastic one-proton-transfer reactions. By-products of the main investigation were two well-developed rotational bands which were identified in heavy reaction partner products complementary to {sup 137}Cs and are tentatively assigned to the little studied nucleus {sup 231}Ac. There was no difficulty in placing the 11 observed {sup 137}Cs transitions in a yrast level scheme extending to an I{sup {pi}}=(31/2{sup {minus}}) level at 5494 keV. Interpretation was also straightforward, since the experimental level energies are in close agreement with results of shell model calculations performed earlier using empirical single particle energies and interaction matrix elements derived from experimental data for other N=82 isotones. {copyright} {ital 1999} {ital The American Physical Society}

Yrast excitations in A = 126–131 Te nuclei from deep inelastic 130Te+ 64Ni reactions

Thick target γγ coincidence measurements for the system 130Te + 275 MeV 64Ni have been performed using the GASP Ge detector array at Legnaro. For the isotopic assignments of previously unknown γ-ray cascades, prompt γγ coincidences observed between Te and Ni partner products were of vital importance. The results yield much new information about excited states of moderate spins in A = 126–131 tellurium nuclei, especially about yrast excitations of the little studied odd- A isotopes 127Te, 129Te, and 131Te. Level systematics of tellurium nuclei are presented, and both single-particle and collective aspects of the level spectra are discussed.

Yrast excitations of heavy tin region nuclei

Thick target γγ coincidence measurements have been used to explore the spectroscopy of neutron-rich Z ~ 50 nuclei formed in deep inelastic heavy ion reactions. Yrast isomers in 119Sn, 121Sn and 123Sn have been identified among the products of heavy ion collisions with 124Sn targets 10-15% above the Coulomb barrier, and isomeric decay schemes are reported. For (vh11/2)n seniority-3 states, the observed level energies agree closely with the results of fractional parentage calculations.

Level structure of proton-richN=83 Nuclei150Ho and152Tm

The yrast levels of theN=83 odd-odd nuclei150Ho and152Tm have been studied byγ-ray spectroscopy following reactions induced by 240–250 MeV60Ni ions. Isomers have been identified in150Ho at 1.096, 2.625 and ∼8.0 MeV and in152Tm at 2.555 and ∼ 6.3 MeV, and the level schemes of both nuclei have been established up to 2.6 MeV. The level spectra are interpreted using the shell model in terms of the coupling of anf 7/2,h 9/2 or i13/2 valence neutron to the yrast excitations of the neighboring N=82 nuclei.