Search

High-spin states in $^{76}\mathrm{Sr}$ have been studied using Gammasphere plus Microball detector arrays. The known yrast band has been extended beyond the first band crossing, which involves the simultaneous alignment of pairs of ${\mathrm{g}}_{\frac{9}{2}}$ protons and neutrons, to a tentative spin of $24\ensuremath{\hbar}$. The data are compared with the results of cranked relativistic mean-field (CRMF) and cranked relativistic Hartree-Bogoliubov (CRHB) calculations. The properties of the band, including the ${\mathrm{g}}_{\frac{9}{2}}$ proton/neutron band crossing frequency and moments of inertia, are found to be well reproduced by the CRHB calculations. Furthermore, the unpaired CRMF calculations show quite good agreement with the data beyond the band crossing region, indicating that pairing is weak at these frequencies. The high spin results suggest that there is little evidence for an isoscalar $(t=0)$ $\mathit{np}$ pair field. Moreover, a systematic study of the band crossings in even-even $N=Z$ nuclei for the first time reveals that there is no evidence to support the existence of the Coulomb antipairing effect caused by the Coulomb exchange term.

The Gammasphere spectrometer, in conjunction with the Microball charged-particle array, was used to investigate high-spin states in Te-112 via Ni-58(Ni-58, 4p gamma) reactions at 240 and 250 MeV. Several smooth terminating bands were established, and lifetime measurements were performed for the strongest one using the Doppler-shift attenuation method. Results obtained in the spin range 18-32h yield a transition quadrupole moment of 4.0 +/- 0.5eb, which corresponds to a quadrupole deformation epsilon(2)=0.26 +/- 0.03; this value is significantly larger than the ground-state deformation of tellurium isotopes. It was also possible to extract a transition quadrupole moment for the yrast band in Xe-114, produced via the 58Ni (58Ni, 2p gamma) reaction. A value of 3.0 +/- 0.5eb was found in the spin range 16-24h, which corresponds to a quadrupole deformation epsilon(2)=0.19 +/- 0.03. Cranked Nilsson-Strutinsky calculations are used to interpret the results. (Less)

The influence of the central depression in the density distribution of spherical superheavy nuclei on the shell structure is studied within the relativistic mean field theory. Large depression leads to the shell gaps at the proton Z=120 and neutron N=172 numbers, while flatter density distribution favors N=184 for neutrons and leads to the appearance of a Z=126 shell gap and to the decrease of the size of the Z=120 shell gap. The correlations between the magic shell gaps and the magnitude of central depression are discussed for relativistic and non-relativistic mean field theories., 5 pages

We analyze thermonuclear and pycnonuclear fusion reactions in dense matter containing atomic nuclei of different types. We extend a phenomenological expression for the reaction rate, proposed recently by Gasques et al. (2005) for the one-component plasma of nuclei, to the multi-component plasma. The expression contains several fit parameters which we adjust to reproduce the best microscopic calculations available in the literature. Furthermore, we show that pycnonuclear burning is drastically affected by an (unknown) structure of the multi-component matter (a regular lattice, a uniform mix, etc.). We apply the results to study nuclear burning in a carbon_12-oxygen_16 mixture. In this context we present new calculations of the astrophysical S-factors for carbon-oxygen and oxygen-oxygen fusion reactions. We show that the presence of a CO lattice can strongly suppress carbon ignition in white dwarf cores and neutron star crusts at densities > 3e9 g cm^{-3} and temperatures T, 16 pages, 5 figures, to appear in Phys. Rev. C

High‐spin states in 3674Kr38 were studied using the 40Ca(40Ca,α2p)74Kr fusion evaporation reaction at a beam energy of 165 MeV with GAMMASPHERE and MICROBALL and at a beam energy of 185 MeV with EUROBALL and ISIS multi‐detector arrays. Lifetimes of the high‐spin states for the ground‐state band and the favoured negative‐parity band have been determined using the Doppler‐shift attenuation method. The deduced transition quadrupole moments show a marginal decrease as a function of spin, suggesting that the rotational bands do not terminate at the maximum spin Imax.

We report on a set of in-beam studies of excited states in $^{250}\mathrm{Fm}$. We detected prompt \ensuremath{\gamma} rays by using the JUROSPHERE IV array and conversion electrons by using the SACRED spectrometer. Both devices were used in conjunction with the RITU gas-filled recoil separator located at the University of Jyv\"askyl\"a. $^{250}\mathrm{Fm}$ nuclei were produced through the $^{204}\mathrm{Hg}$($^{48}\mathrm{Ca}$,$2n)$$^{250}\mathrm{Fm}$ fusion-evaporation reaction. An experimental excitation function gave a maximum reaction cross section of (980 \ifmmode\pm\else\textpm\fi{} 160) nb at an energy of 209 MeV in the center of the target. Tagging techniques were employed, and a number of E2 transitions were observed that connected the ground-state band levels from spin ${4}^{+}$ up to ${18}^{+}$. The highly converted ${4}^{+}\ensuremath{\rightarrow}{2}^{+}$ transition is observed only by use of conversion electron spectroscopy. The observed ground-state band transitions indicate a rotational structure. We deduce a quadrupole deformation parameter of ${\ensuremath{\beta}}_{2}=0.28$ \ifmmode\pm\else\textpm\fi{} 0.02. A low-energy background of apparent nuclear origin is observed in conversion electrons and postulated to arise from the decay of high-K bands. The half-life of $^{250}\mathrm{Fm}$ is measured to be 30.4 \ifmmode\pm\else\textpm\fi{} 1.5 min.

Rotating $N=Z$ nuclei in the mass $A=58-80$ region have been studied within the framework of isovector mean field theory. Available data is well and systematically described in the calculations. The present study supports the presence of strong isovector $np$ pair field at low spin, which is, however, destroyed at high spin. No clear evidence for the existence of the isoscalar $t=0$ $np$ pairing has been found., Comment: Invited talk presented at the XIII Nuclear Physics Workshop, Kazimierz Dolny, Sept. 27 - Oct. 1, Poland; submitted to International Journal of Modern Physics E

Three rotational bands in 74Kr were studied up to (in one case one transition short of) the maximum spin I(max) of their respective single-particle configurations. Their lifetimes have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments reveal a modest decrease, but far from a complete loss of collectivity at the maximum spin I(max). This feature, together with the results of mean field calculations, indicates that the observed bands do not terminate at I = I(max).

The superdeformation and hyperdeformation in $^{108}$Cd have been studied for the first time within the framework of the fully self-consistent cranked mean field theory, namely, cranked relativistic mean field theory. The structure of observed superdeformed bands 1 and 2 have been analyzed in detail. The bumps seen in their dynamic moments of inertia are explained as arising from unpaired band crossings. This is contrary to an explanation given earlier within the framework of projected shell model. It was also concluded that this nucleus is not doubly magic SD nucleus.

In-beam {gamma}-ray spectroscopic measurements have been made on {sub 102}{sup 253}No. A single rotational band was identified up to a probable spin of 39/2({Dirac_h}/2{pi}), which is assigned to the 7/2{sup +}[624] Nilsson configuration. The bandhead energy and the moment of inertia provide discriminating tests of contemporary models of the heaviest nuclei. Novel methods were required to interpret the sparse data set associated with cross sections of around 50 nb. These methods included comparisons of experimental and simulated spectra, as well as testing for evidence of a rotational band in the {gamma}{gamma} matrix.

In this paper we analyze the nuclear fusion rate between equal nuclei for all five different nuclear burning regimes in dense matter (two thermonuclear regimes, two pycnonuclear ones, and the intermediate regime). The rate is determined by Coulomb barrier penetration in dense environments and by the astrophysical S-factor at low energies. We evaluate previous studies of the Coulomb barrier problem and propose a simple phenomenological formula for the reaction rate which covers all cases. The parameters of this formula can be varied, taking into account current theoretical uncertainties in the reaction rate. The results are illustrated for the example of the ^{12}C+^{12}C fusion reaction. This reaction is very important for the understanding of nuclear burning in evolved stars, in exploding white dwarfs producing type Ia supernovae, and in accreting neutron stars. The S-factor at stellar energies depends on a reliable fit and extrapolation of the experimental data. We calculate the energy dependence of the S-factor using a recently developed parameter-free model for the nuclear interaction, taking into account the effects of the Pauli nonlocality. For illustration, we analyze the efficiency of carbon burning in a wide range of densities and temperatures of stellar matter with the emphasis on carbon ignition at densities rho > 10^9 g/cc., 22 pages, 6 figures, accepted for publication in PRC

We present a review of recent applications of self-consistent relativistic mean-field models to exotic nuclear structure. Based on concepts of non-renormalizable effective relativistic field theories and density functional theory, these models provide a rich theoretical framework for studies of nuclei along the valley of beta-stability, exotic nuclei with extreme ground-state isospin values and close to the particle drip lines. A quantitative microscopic description of ground states and properties of excited states in nuclei far from stability necessitates a unified description of mean-field and pairing correlations. The relativistic Hartree-Bogoliubov (RHB) model has been employed in studies of structure phenomena that include: the description of the neutron drip line in light nuclei and the microscopic mechanism for the formation of neutron halos ; the reduction of the effective spin-orbit interaction and the resulting modification of surface properties in drip line nuclei ; the suppression of shell effects and the onset of deformation and shape coexistence in neutron-rich nuclei ; nuclei at the proton drip-line and ground-state proton emitters in the region of deformed rare-earth nuclei ; shape coexistence phenomena in neutron-deficient nuclei. The cranked RHB framework has been used for the description of rotational excitations: superdeformed and highly deformed rotational bands in the mass Anot, vert, similar60 region, rotational bands built on superdeformed minima in the Anot, vert, similar140-150 and the Anot, vert, similar190 mass regions, and on normal deformed minima in the rare-earth region, smooth termination of rotational bands, rotational and quasiparticle properties of the heaviest actinide nuclei. The relativistic random phase approximation (RRPA) has been employed in studies of nuclear compression modes, nuclear matter asymmetry energy, multipole giant resonances and low-lying collective states in spherical nuclei, the evolution of the low-lying isovector dipole response in nuclei with a large neutron excess, pygmy resonances, isoscalar dipole and toroidal dipole resonances. The relativistic quasiparticle RPA, formulated in the canonical single-nucleon basis of the RHB, has been applied in the description of the low-energy multipole response of unstable weakly bound nuclei. The self-consistent relativistic mean-field framework has been extended to include density-dependent meson-nucleon vertex functions. Compared with standard relativistic effective interactions with non-linear meson-exchange terms, the density-dependent meson-nucleon couplings provide an improved description of asymmetric nuclear matter, neutron matter and nuclei far from stability. Effective density-dependent interactions have also been used in relativistic (Q)RPA calculations of giant resonances, and in a microscopic analysis of the nuclear matter compressibility and symmetry energy.

A systematic investigation of the rotating $N=Z$ even-even nuclei in the mass $A=58-80$ region has been performed within the frameworks of the Cranked Relativistic Mean field, Cranked Relativistic Hartree Bogoliubov theories and cranked Nilsson-Strutinsky approach. Most of the experimental data is well accounted for in the calculations. The present study suggests that there is strong isovector $np$-pair field at low spin, the strength of which is defined by the isospin symmetry. At high spin, the isovector pair field is destroyed and the data are well described by the calculations assuming zero pairing. No clear evidence for the existence of the isoscalar $t=0$ $np$-pairing has been obtained in the present investigation., 20 pages + 19 figures, submitted to Phys. Rev. C

The influence of the central depression in the density distribution of spherical superheavy nuclei on the shell structure is studied within the relativistic mean field theory. Large depression leads to the shell gaps at the proton Z = 120 and neutron N = 172 numbers, while flatter density distribution favors N = 184 for neutrons and leads to the appearance of a Z = 126 shell gap and to the decrease of the size of the Z = 120 shell gap. The correlations between the magic shell gaps and the magnitude of central depression are discussed for relativistic and non‐relativistic mean field theories.

Six rotational bands up to energies E x = 24.7 MeV and spins Jπ=(79/2−) have been identified in 109Sn using the GAMMASPHERE γ-detector array. Four of the bands show smoothly decreasing dynamic moments of inertia at rotational frequencies ℏω > 0.6 MeV. The bands arise at medium spins from a coupling of a valence d5/2, g7/2 or h11/2 neutron to the deformed 2p2h proton excitation of the Z=50 core 108Sn. At very high ℏω these bands show the typical behaviour of smoothly terminating bands, i.e. a gradual alignment of the angular momenta of the valence particles and holes corresponding to a transition from high collectivity to noncollective states.

Two experiments have been performed using the Ni-58(S-32,3p) reaction at 135 MeV with Gammasphere and the Microball to study the high-spin structure of the transitional nucleus Nb-87. The first experiment using a thin target provided a considerable extension and refinement of the level scheme, as well as firm spin assignments from directional correlation of oriented nuclei. Sub-picosecond lifetimes were measured in the second backed-target experiment using the Doppler-shift attenuation method. The lifetimes imply a rather modest average deformation of beta(2)similar to0.1, but with considerable variation from state to state. Strong alternations were observed in the B(M1) strengths of transitions between some pairs of bands. The experimental results were compared with calculations performed within the cranked Nilsson-Strutinsky approach. The calculations generally reproduce the irregularities in the structure of the yrast lines and plunging transition quadrupole moments Q(t) within the bands explaining them as reflections of configuration changes and an approach of band termination, respectively. (Less)

High-spin states in the odd-odd N=Z nucleus Rb-74(37)37 were studied using the Ca-40(Ca-40,alphanp) reaction. A previously observed odd-spin T=0 band has been extended to I-pi=(31(+)) and an even-spin T=0 band has been observed for the first time to I-pi=(22(+)); both have a pi(g(9/2))circle timesnu(g(9/2)) structure. A strongly coupled low-spin T=0,K=3 band has been interpreted as being based upon a pi[312]3/2 circle timesnu[312]3/2 configuration. Cranked relativistic Hartree-Bogoliubov calculations, which are corrected for the t=1 np-pair field by restoring isospin symmetry, reproduce the observed spectrum. These new results provide evidence for the existence of an isovector pair field that contains a neutron-proton component with the proper strength for ensuring isospin conservation. (Less)

The cranked relativistic Hartree+Bogoliubov theory has been applied for a systematic study of the nuclei around 254No, the heaviest elements for which detailed spectroscopic data are available. The deformation, rotational response, pairing correlations, quasi-particle and other properties of these nuclei have been studied with different parametrizations for the effective mean-field Lagrangian. Pairing correlations are taken into account by a finite range two-body force of Gogny type. While the deformation properties are well reproduced, the calculations reveal some deficiencies of the effective forces both in the particle-hole and particle-particle channels. For the first time, the quasi-particle spectra of odd deformed nuclei have been calculated in a fully self-consistent way within the framework of the relativistic mean field (RMF) theory. The energies of the spherical subshells, from which active deformed states of these nuclei emerge, are described with an accuracy better than 0.5 MeV for most of the subshells with the NL1 and NL3 parametrizations. However, for a few subshells the discrepancies reach 0.7-1.0 MeV. In very heavy systems, where the level density is high, this level of accuracy is not sufficient for reliable predictions of the location of relatively small deformed shell gaps. The calculated moments of inertia reveal only small sensitivity to the RMF parametrization and, thus, to differences in the single-particle structure. However, in contrast to lighter systems, it is necessary to decrease the strength of the D1S Gogny force in the pairing channel in order to reproduce the moments of inertia., 32 pages, 30 figures (Encapsulated Postscript), Revtex, uses epsf.sty, submitted to Physical Review C

The cranked relativistic Hartree+Bogoliubov theory has been applied for a systematic study of the nuclei around 254No, the heaviest nuclei for which detailed spectroscopic data are available. The deformation, rotational response, pairing correlations, quasi-particle and other properties of these nuclei have been studied with different relativistic mean field (RMF) parametrizations. For the first time, the quasi-particle spectra of odd deformed nuclei have been calculated in a fully self-consistent way within the framework of the RMF theory. The energies of the spherical subshells, from which active deformed states of these nuclei emerge, are described with an accuracy better than 0.5 MeV for most of the subshells with the NL1 and NL3 parametrizations. However, for a few subshells the discrepancy reach 0.7-1.0 MeV. The implications of these results for the study of superheavy nuclei are discussed., 7 pages, 3 figures, Proceedings of the Conference on Frontiers of Nuclear Structure, Berkeley, California, July 29th - August 2nd, 2002, UC Berkeley, Clark Kerr Campus, in press

Excited states in ${}^{70}\mathrm{Br}$ were populated in the ${}^{40}\mathrm{Ca}{(}^{32}\mathrm{S},pn)$ reaction at ${E}_{\mathrm{beam}}=80--100 \mathrm{MeV}$ and the ${}^{40}\mathrm{Ca}{(}^{36}\mathrm{Ar},\ensuremath{\alpha}pn)$ reaction at ${E}_{\mathrm{beam}}=145 \mathrm{MeV}.$ The resulting gamma decay was detected using the Gammasphere array triggered by a 30-element neutron detector. The cross-bombardment allowed the unambiguous assignment of levels to ${}^{70}\mathrm{Br},$ comprising a total of 32 states built both on the ${J}^{\ensuremath{\pi}}{=0}^{+}$ ground state and a previously known ${J}^{\ensuremath{\pi}}{=9}^{+}$ isomer, which is located at an excitation energy of 2293 keV by the observation of linking transitions. The structures are discussed within the context of the two-quasiparticle plus rotor model, the IBM-4 model and the cranked Nilsson-Strutinsky formalism. The nonobservation of a doublet of $J=0,$ $T=1$ and $J=1,$ $T=0$ states at low excitation in ${}^{70}\mathrm{Br}$ is indicative that $T=0$ proton-neutron pairing strength is weak in comparison to $T=1$ pairing.

Excited states in the N=Z+1 nucleus Kr-73 have been investigated using the Ca-40(Ar-36,2pn) and Ca-40(Ca-40,alpha2pn) reactions at 145 and 160 MeV, respectively. gamma rays were detected using the Gammasphere array and events were recorded in coincidence with charged-particle and neutron detectors. The three previously observed bands were extended to high spin, and a new unfavored positive-parity band has been observed. The alignment characteristics and decay properties of the bands are all consistent with large-deformation prolate rotation, with no clear evidence for oblate bands or shape coexistence. This is quite different from neighboring Kr-72,Kr-74, indicating a strong shape-stabilizing role for the valence neutron. The experimental results are compared to extended total Routhian surface, cranked Nilsson Strutinsky, and cranked relativistic mean-field calculations. The results suggest that the paired calculations lack some important physics. Neutron-proton correlations may be the missing ingredient. There is also evidence for an unusual band crossing in the negative-parity bands, which may indicate the presence of T=0 pairing correlations. At high spin all the models can reproduce the experimental data.

The latest generation gamma-ray detection system, GAMMASPHERE, coupled with the Microball charged-particle detector, has made possible a new class of nuclear lifetime measurement. For the first time differential lifetime measurements free from common systematic errors for over 15 different nuclei ( >30 rotational bands in various isotopes of Ce, Pr, Nd, Pm, and Sm) have been extracted at high spin within a single experiment. This comprehensive study establishes the effective single-particle transition quadrupole moments in the A approximately 135 light rare-earth region. Detailed comparisons are made with theoretical calculations using the self-consistent cranked mean-field theory which convincingly demonstrates the validity of the additivity of single-particle quadrupole moments in this mass region.

The development of self-consistent microscopic many-body theories aiming at the description of low-energy nuclear phenomena provides the necessary theoretical tools for an exploration of the nuclear chart into known and unknown regions. As discussed throughout this Workshop, the relativistic mean field (RMF) theory is one of them. It has been very successful in the investigation of different aspects of the many-body problem in nuclear physics [1], as for example the properties of rotating nuclei. Initiated by the Munich group the cranked relativistic mean field (CRMF) theory [2, 3, 4, 5], in which pairing is neglected, and cranked relativistic Hartree-Bogoliubov (CRHB) theory [6, 7] have been developed as extensions of RMF theory for the description of such systems. As follows from studies of super-and normal-deformed rotational bands in different regions of the periodic table (see Refs. [5, 7, 8, 9, 10] and references quoted therein), they provide a very good description of the experimental data.

A rotational band with seven gamma -ray transitions between states with spin 2 (h) over bar and 16 (h) over bar has been observed in the doubly magic, self-conjugate nucleus Ca-40(20)20. The measured transition quadrupole moment of 1.80(-0.29)(+0.39)eb indicates a superdeformed shape with a deformation beta (2) = 0.59(-0.07)(+0.11). The features of this band are explained by cranked relativistic mean field calculations to arise from an 8-particle 8-hole excitation.

The latest generation gamma-ray detection system, GAMMASPHERE, coupled with the Microball charged-particle detector, has made possible a new class of nuclear lifetime measurement. For the first time differential lifetime measurements free from common systematic errors for over 15 different nuclei (30 rotational bands in various isotopes of Ce, Pr, Nd, Pm, and Sm) have been extracted at high spin within a single experiment. This comprehensive study establishes the effective single-particle transition quadrupole moments in the A approximately 135 light rare-earth region. Detailed comparisons are made with theoretical calculations using the self-consistent cranked mean-field theory which convincingly demonstrates the validity of the additivity of single-particle quadrupole moments in this mass region.

High spin states have been studied in the nucleus {sup 100}Pd with the aim of investigating the novel phenomenon of ''antimagnetic rotation.'' A cascade of four ''rotational-band-like'' transitions is proposed as corresponding to antimagnetic rotation, based on the observed spectroscopic properties and a comparison with calculations in the configuration-dependent cranked Nilsson-Strutinsky formalism.

A rotational band with seven gamma-ray transitions between states with spin 2 Planck's constant and 16 Planck's constant has been observed in the doubly magic, self-conjugate nucleus (40)(20)Ca(20). The measured transition quadrupole moment of 1.80(+0.39)(-0.29)eb indicates a superdeformed shape with a deformation beta(2) = 0.59(+0.11)(-0.07). The features of this band are explained by cranked relativistic mean field calculations to arise from an 8-particle 8-hole excitation.

A systematic investigation of the yrast superdeformed (SD) rotational bands in even-even nuclei of the $A\sim 190$ mass region has been performed within the framework of the cranked relativistic Hartree-Bogoliubov theory. The particle-hole channel of this theory is treated fully relativistically, while a finite range two-body force of Gogny type is used in the particle-particle (pairing) channel. Using the well established parameter sets NL1 for the Lagrangian and D1S for the Gogny force, very good description of experimental data is obtained with no adjustable parameters., 5 pages, 2 Postscript figures, uses sprocl.sty, contribution to the Proceedings of the International Conference ``Bologna 2000, Structure of the Nucleus at the Dawn of the Century''

High-spin states in Cu-59 were populated using the fusion-evaporation reactions Si-28+ Ca-40 at a beam energy of 125 MeV and Ar-36+Si-28 at a beam energy of 143 MeV. The Gammasphere array in conjunction with ancillary detector systems allowed for the identification of a superdeformed rotational band in Cu-59, which was firmly linked to low-spin yrast states. Using directional correlations of oriented states, a spin-parity assignment of I-pi=25/2(+) to the band head was possible. The average quadrupole moment of the band is measured to be Q(t)=(2.24+/-0.40) e b. The characteristics of the band are compared to neighboring nuclei and predictions of different mean-field theories.

Four highly deformed structures in the odd-odd nucleus {sub 61}{sup 136}Pm{sub 75} were observed via the {sup 105}Pd({sup 35}Cl,2p2n) reaction at 180 and 173 MeV using the GAMMASPHERE {gamma}-ray spectrometer and the Microball charged-particle detector array. Quadrupole moment measurements were performed on all of the bands. In contrast to lighter odd-Z Pm and Pr nuclei, bands based on the g{sub 9/2}[404]9/2 proton orbital were not observed. Instead, the four observed sequences are assigned as a coupling of an i{sub 13/2} neutron with the low-{omega} h{sub 11/2} and mixed d{sub 5/2}g{sub 7/2} orbitals. Comparisons with neighboring highly deformed structures are discussed and cranked Nilsson-Strutinsky calculations for {sup 136}Pm are presented. (c) 2000 The American Physical Society.

Very high spin states $(I=50--60\ensuremath{\Elzxh})$ have been observed in the transitional nuclei ${}^{161}\mathrm{Er}$ and ${}^{162}\mathrm{Er}$ using the Euroball $\ensuremath{\gamma}$-ray spectrometer. In ${}^{161}\mathrm{Er},$ three bands are observed well above spin $50\ensuremath{\Elzxh}.$ In the positive parity, positive signature $(+,+\frac{1}{2})$ band a discontinuity in the regular rotational behavior occurs at ${\frac{109}{2}}^{+}$ and a splitting into two branches occurs at ${\frac{97}{2}}^{\ensuremath{-}}$ in the negative parity, positive signature $(\ensuremath{-},+\frac{1}{2})$ band. The $(\ensuremath{-},\ensuremath{-}\frac{1}{2})$ band continues in a regular fashion to ${\frac{115}{2}}^{\ensuremath{-}},$ tentatively $({\frac{119}{2}}^{\ensuremath{-}}).$ In ${}^{162}\mathrm{Er}$ the positive parity, even spin (+,0) yrast band is observed to continue smoothly up to ${58}^{+}$ ${(60}^{+})$ and the negative parity, even spin $(\ensuremath{-},0)$ and odd spin $(\ensuremath{-},1)$ bands are extended from ${30}^{\ensuremath{-}}$ to ${34}^{\ensuremath{-}}$ and from ${31}^{\ensuremath{-}}$ to ${47}^{\ensuremath{-}}$ ${(49}^{\ensuremath{-}}),$ respectively. The high spin experimental spectra are compared with both a simple model involving the occupation of specific single neutron states in the absence of neutron pair correlations and with more detailed cranked Nilsson-Strutinsky calculations in which both proton and neutron pairing correlations are neglected. The very high spin domain is found to comprise a series of unpaired rotational bands. Unpaired band crossings between bands with different neutron and proton configurations are identified in ${}^{161}\mathrm{Er}.$ There is no evidence for aligned oblate or terminating states being close to the yrast line in ${}^{161,162}\mathrm{Er}$ up to spin $\ensuremath{\approx}60\ensuremath{\Elzxh}$ in contrast to the lighter Er isotopes.

The microscopic role of nuclear magnetism in rotating frame is investigated for the first time in the framework of the cranked relativistic mean field theory. It is shown that nuclear magnetism modifies the expectation values of single-particle spin, orbital and total angular momenta along the rotational axis effectively creating additional angular momentum. This effect leads to the increase of kinematic and dynamic moments of inertia at given rotational frequency and has an impact on effective alignments., 16 pages, 4 figures, submitted to Physical Review C

High-spin states in the near proton-dripline nucleus {sup 107}Sb have been identified, and collectivity in this nucleus has been observed for the first time in the form of two rotational bands. One of the observed rotational structures is a {delta}I=1 band, and is interpreted as based on a {pi}(g{sub 9/2}){sup -1}(multiply-in-circle sign){pi}(g{sub 7/2}d{sub 5/2}){sup 2} proton configuration. A second structure has {delta}I=2 character, and is explained as being based on a {pi}h{sub 11/2}(multiply-in-circle sign)[{pi}(g{sub 9/2}){sup -2}(multiply-in-circle sign){pi}(g{sub 7/2}d{sub 5/2}){sup 2}] proton configuration through comparison with cranked Nilsson-Strutinsky model calculations. The calculations predict that this band terminates at a spin of 79/2 ({Dirac_h}/2{pi}). (c) 2000 The American Physical Society.

Excited states have been identified in the very neutron-deficient ${}^{119}\mathrm{Ba}$ nucleus. Two bands have been observed, which are likely to be based on ${h}_{11/2}$ and ${(g}_{7/2}{d}_{5/2})$ neutron orbitals. Despite this being the first observation of excited states in ${}^{119}\mathrm{Ba},$ the bands extend to $(75/2)\ensuremath{\Elzxh}$ and $(79/2)\ensuremath{\Elzxh},$ respectively. The bands have been assigned to ${}^{119}\mathrm{Ba}$ using gamma-recoil and gamma--x-ray coincidences. Several quasiparticle alignments have been identified, involving neutron ${(h}_{11/2}{)}^{2}$ and proton ${(h}_{11/2}{)}^{2}$ aligned configurations. Furthermore, the bands show features which are reasonably consistent with smooth band termination at high spin. Theoretical results for ${}^{119}\mathrm{Ba}$ are discussed within the framework of cranked Woods-Saxon and Nilsson-Strutinsky calculations.

High-spin states in {sup 86}Zr up to 30{sup +} and 27{sup -} were observed via the {sup 58}Ni({sup 32}S,4p) reaction at 135 MeV beam energy using the combined GAMMASPHERE and MICROBALL systems. Calculations performed with the configuration-dependent shell-correction approach show that these states are built from six g{sub 9/2} neutrons and at most four protons excited from the p{sub 1/2},p{sub 3/2},f{sub 5/2} subshells to the g{sub 9/2} subshell at small deformation. The highest observed states at 27{sup -} and 30{sup +} are interpreted as band-terminating states with the latter having the highest spin available in the valence space for {sup 86}Zr. (c) 2000 The American Physical Society.

The rotational and deformation properties of superdeformed fission isomers in the $A\sim 240$ mass region have been investigated within the framework of the cranked relativistic Hartree-Bogoliubov theory. The dependence of the results of the calculations on the parametrization of the RMF Lagrangian has been studied. The rotational properties are best described by the NL1 force., Comment: 5 pages, uses epsf.sty and hip-artc.sty, 1 PostScript figure, contribution to the Proceedings of the International Symposium on Exotic Nuclear Structures, May 15-20, 2000, Debrecen, Hungary

Cranked Relativistic Hartree-Bogoliubov theory without and with approximate particle number projection by means of the Lipkin-Nogami method is presented in detail as an extension of Relativistic Mean Field theory with pairing correlations to the rotating frame. Pairing correlations are taken into account by a finite range two-body force of Gogny type. The applicability of this theory to the description of rotating nuclei is studied in detail on the example of superdeformed bands in even-even nuclei of the $A\sim 190$ mass region. Different aspects such as the importance of pairing and particle number projection, the dependence of the results on the parametrization of the RMF Lagrangian and Gogny force etc. are investigated in detail. It is shown that without any adjustment of new parameters the best description of experimental data is obtained by using the well established parameter sets NL1 for the Lagrangian and D1S for the pairing force. Contrary to previous studies at spin zero it is found that the increase of the strength of the Gogny force is not necessary in the framework of Relativistic Hartree-Bogoliubov theory provided that particle number projection is performed., Comment: 34 pages, 24 figures, 3 tables, uses Revtex and epsf.sty, submitted to Nuclear Physics A

The nuclei ${}^{138}\mathrm{Nd}$ and ${}^{139}\mathrm{Nd}$ have been studied at very high spins via the ${}^{48}\mathrm{Ca}{+}^{94}\mathrm{Zr}$ reaction. Several new rotational bands were observed, four in ${}^{138}\mathrm{Nd}$ and two in ${}^{139}\mathrm{Nd}.$ The ${J}^{(2)}$ moments of inertia calculated from the observed $\ensuremath{\gamma}$-ray energies are very small and almost constant, indicating that these bands are triaxial. Cranked Nilsson-Strutinsky calculations reproduce the general behavior of the bands, supporting this interpretation and suggesting an approximately constant $\ensuremath{\gamma}$ value of $\ensuremath{\sim}+35\ifmmode^\circ\else\textdegree\fi{}$ over a large spin range up to the highest observed spins. These bands and a few similar bands in other nuclei of the $N\ensuremath{\approx}80$ region are a unique example of almost undisturbed triaxial bands.

Cranked Relativistic Hartree-Bogoliubov (CRHB) theory is presented as an extension of Relativistic Mean Field theory with pairing correlations to the rotating frame. Pairing correlations are taken into account by a finite range two-body force of Gogny type and approximate particle number projection is performed by Lipkin-Nogami method. This theory is applied to the description of yrast superdeformed rotational bands observed in even-even nuclei of the $A\sim 190$ mass region. Using the well established parameter sets NL1 for the Lagrangian and D1S for the pairing force one obtains a very successful description of data such as kinematic ($J^{(1)}$) and dynamic ($J^{(2)}$) moments of inertia without any adjustment of new parameters. Within the present experimental accuracy the calculated transition quadrupole moments $Q_t$ agree reasonably well with the observed data., 6 pages including 4 PostScript figures, uses RevTex, revised version, Phys.Rev. C, Rapid Communications, in press

The level scheme of ${}^{103}\mathrm{Pd}$ has been reconstructed using high-fold $\ensuremath{\gamma}$-ray coincidence data obtained with the EUROGAM-2 spectrometer in the ${}^{70}\mathrm{Zn}{(}^{36}\mathrm{S},3n)$ reaction at $E=130\mathrm{MeV}.$ New spins and excitation energies are given for levels in the strongly coupled positive parity bands. Four high-spin bands are discussed in terms of terminating configurations using Nilsson-Strutinsky cranking calculations. One of them, having valence-space configuration, is observed up to its predicted terminating state of ${I}^{\ensuremath{\pi}}{=65/2}^{+}.$ Another band, which is possibly observed up to its terminating state at $Ig40,$ is assigned to have a $2p\ensuremath{-}2h$ core-excited configuration.

Three long, strongly coupled (ΔI=1) sequences have been identified in 110,112Te by using the GAMMASPHERE array in conjunction with the MICROBALL charged-particle array. These bands are interpreted in terms of deformed proton 1-particle–1-hole bands that reach termination at I∼40ℏ. This is the first observation of such collective dipole structures in this mass region. In contrast, many shorter dipole sequences have been associated with weakly deformed structures that generate angular momentum by the shears mechanism (magnetic rotation).

The cranked relativistic mean field (CRMF) theory is applied for the description of superdeformed (SD) rotational bands observed in $^{153}$Ho. The question of the structure of the so-called SD band in $^{154}$Er is also addressed and a brief overview of applications of CRMF theory to the description of rotating nuclei at extreme conditions is presented., Comment: 4 pages, 1 PostScript figure, LaTex, uses 'espcrc1.sty', to be published in Proceedings of International Nuclear Physics Conference, Paris, 1998 which will appear in Nuclear Physics

Lifetime measurements of states in the yrast band of 119Xe have been performed using a Doppler broadened lineshape analysis. Preliminary results, in the range 27/2−⩽Iπ⩽43/2−, indicate a transition quadrupole moment of approximately 2.9 eb, which corresponds to a prolate rotor with deformation e2≈0.17.

The level structure of102Rh has been investigated using the EUROGAM Phase2 array. Bands observed up to high spins are discussed in terms of band terminations.102Rh is the first doubly odd nucleus belowZ = 50 in which band terminations are established.

We consider bound states (BS) of quasi-soliton pulses in the quintic Ginzburg-Landau (GL) equation and in the driven damped nonlinear Schrodinger equation. Using the perturbation theory, we derive dynamical systems describing the interaction between weakly overlapping pulses in both models and formation of bound states. While all BS’s in the GL model are unstable, one of them has very weak instability, so it can be considered stable for applications. For the damped driven model, we demonstrate the existence of fully stable BS’s, provided that the amplitude of the driving field exceeds a very low threshold.

It is shown that self-guided optical beams with power-law asymptotics, i.e., algebraic optical solitons, can be regarded as a special case of sech-type solitons (i.e. solitons with exponentially decaying asymptotics) in the limit where the beam propagation constant coincides with the threshold for linear wave propagation. This leads to the conjecture that algebraic optical solitons should be inherently unstable due to interactions with linear waves, even in cases when the corresponding family of sech-type solitons is stable. This conjecture is verified numerically for a wide class of optical solitons described by the generalized nonlinear Schr\"odinger equation with two competing nonlinearities. \textcopyright{} 1996 The American Physical Society.

Nonlinear theory describing the instability-induced dynamics of dark solitons in the generalized nonlinear Schrodinger equation is presented. Equations for the evolution of an unstable dark soliton, including its transformation into a stable soliton, are derived using a multiscale asymptotic technique valid near the soliton instability threshold. Results of the asymptotic theory are applied to analyze dark solitons in physically important models of optical nonlinearities, including competing, saturable, and transiting nonlinearities. It is shown that in all these models dark solitons may become unstable, and two general ~bounded and unbounded! scenarios of the instability development are investigated analytically. Results of direct numerical simulations of the generalized nonlinear Schrodinger equation are also presented, which confirm predictions of the analytical approach and display main features of the instability-induced dynamics of dark solitons beyond the applica- bility limits of the multiscale asymptotic theory. @S1063-651X~96!09707-3#

We propose an approach to numerical analysis of soliton interactions in dynamical systems described by the Ginzburg-Landau equation. This approach is based on the analysis of soliton trajectories in a phase plane. The main features of the interaction are represented in sufficient detail to permit understanding of the formation of bound states and their stability. Among the bound states we find some with \ensuremath{\pi}/2 out-of-phase solitons. \textcopyright{} 1996 The American Physical Society.

We report numerical observation of two new forms of stable localized solutions of the quintic complex Ginzburg-Landau equation. The first form is a stationary zero-velocity solution, which consists of two motionless fronts and a source between them. We call this structure the >composite> pulse. We show that in some range of parameters, a composite pulse can coexist with a plain pulse solution. At the boundary of their region of existence in the parameter space, composite pulses exhibit a complicated behavior, which includes periodical dynamics and transition into another new form of localized solutions, namely, uniformly translating, or moving pulses. A careful study shows that the moving pulses have an even wider range of existence than the composite pulses. The interactions between different combinations of moving and stationary pulses are also studied. A qualitative explanation of the observed structures is proposed., The work of V.V.A. and N.A. was supported by the Australian Photonics Cooperative Research Centre (APCRC). The work of J.M.S.-C. was supported by the CICyT under Contract No. TIC95-0563-03.