The mass distribution for excess dielectrons in S+Au collisions at $200A$ GeV measured by the CERES Collaboration at the CERN Super Proton Synchrotron is analyzed. The data are seen to be in satisfactory agreement with a scenario where a thermalized quark-gluon plasma is formed initially, which expands, cools, hadronizes, and undergoes a freeze-out. The same treatment is also seen to provide a reasonable description for the excess dimuons measured by the HELIOS/3 experiment for S+W collisions.

Proton-drip-line nuclei ${}_{}{}^{26}{}_{}{}^{}\mathrm{P}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{S}$ are studied in the nonlinear relativistic mean-field theory. Calculations show that the mean-square radius of protons in the $2s_{\frac{1}{2}}$ state is approximately 18-20 ${\mathrm{fm}}^2$ which is abnormally large as compared with the mean-square radii of proton, neutron, and matter distributions, giving a strong evidence for proton halos in ${}_{}{}^{26}{}_{}{}^{}\mathrm{P}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{S}$. This indicates that the size of proton halos is as large as that of neutron halos although there exists the Coulomb barrier in proton-drip-line nuclei.

The ${\mathrm{\beta }}^{+}$ decay of 15.2 min ${}_{}{}^{114}{}_{}{}^{}\mathrm{Te}$ into levels of ${}_{}{}^{114}{}_{}{}^{}\mathrm{Sb}$ was studied through γ-ray and conversion electron spectroscopy at the UNISOR on-line isotope mass separator. Multiscaled γ-ray and electron singles provided for the determination of energies and intensities for 94 transitions (68 new) and of internal conversion coefficients for 12 of these transitions. The level scheme was deduced from γ-γ and γ-e coincidence measurements and extended to 2.1 MeV. The energy spectrum and electromagnetic properties of levels and associated transitions were calculated in the interacting boson-fermion-fermion model (IBFFM), with good agreement between experimental and theoretical results. © 1996 The American Physical Society.

High angular momentum states in ${}_{}{}^{195\mathrm{-}197}{}_{}{}^{}\mathrm{Bi}$ are populated in two reactions: ${}_{}{}^{183}{}_{}{}^{}\mathrm{W}$${(}^{19}$F,xn${)}^{202\mathrm{-}\mathit{x}}$Bi and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$${(}^{20}$Ne,xn${)}^{201\mathrm{-}\mathit{x}}$Bi at beam energies of 108 and 123 MeV, respectively. Gamma rays were detected using the Gammasphere array. Three weakly populated rotational sequences have been found. They each have properties characteristic of other superdeformed bands in this mass region. On the basis of cross-bombardment information we believe that one band belongs to each of ${}_{}{}^{195}{}_{}{}^{}\mathrm{Bi}$, ${}_{}{}^{196}{}_{}{}^{}\mathrm{Bi}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Bi}$. The properties of the bands in the odd-Bi nuclei are best reproduced if the odd proton occupies the favored signature of the [651]1/2 orbital, while the band in ${}_{}{}^{196}{}_{}{}^{}\mathrm{Bi}$ has this same proton configuration coupled to an additional N=7 (${\mathit{j}}_{15/2}$) neutron. The relative behavior of the ${\mathfrak{J}}^{\mathrm{}\left(2\right)\mathrm{}}$ moments of inertia can be qualitatively understood in terms of Pauli-blocking effects. © 1996 The American Physical Society.

A series of low temperature nuclear orientation (LTNO) experiments has been initiated to measure accurately ground-state magnetic dipole moments of a sequence of odd-proton antimony isotopes up to the neutron shell closure at N=82 using the sensitive technique of nuclear magnetic resonance on oriented nuclei (NMR/ON). The main aim of this investigation is to clarify the single-particle+collective core coupling mechanism in the heavy antimony isotopes and its influence on the value of magnetic dipole moment. This paper reports results of precision measurement of the magnetic dipole moments of ${}_{}{}^{127}{}_{}{}^{}\mathrm{Sb}$ and ${}_{}{}^{129}{}_{}{}^{}\mathrm{Sb}$. © 1996 The American Physical Society.

At the newly installed 180° Darmstadt electron scattering facility we have measured the isovector M1 transition strengths in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ in the excitation energy range from 10 to 18 MeV. Overall agreement with a shell-model calculation using the unified sd-shell interaction and effective g factors is obtained. Comparison with Gamow-Teller strength deduced from (p,n) data reveals the presence of meson exchange current contributions of the order of 25% to the summed M1 transition strength. © 1996 The American Physical Society.

The angular distributions of the cross sections of reactions to levels up to ${\mathit{E}}_{\mathit{X}}$=11 MeV in ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$ were measured for the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${(}^6$Li,d) at E=37 MeV. These angular distributions for the unbound states, particularly the well populated 7.67(${10}^{+}$), 8.04(${12}^{+}$), 8.54, 8.96, 9.58, and 10.86 MeV states, were analyzed together with the data at E=50 MeV using α-particle wave functions calculated at the resonance energies using the squared Woods-Saxon potentials. The strongly excited state at ${\mathit{E}}_{\mathit{X}}$=10.86 MeV, whose spin parity was not identified from the data at 50 MeV, was found to be a candidate for the bandhead state of the higher nodal ${\mathit{K}}^{\mathrm{\pi }}$=$0^{+}$ band with principal quantum number N=14. © 1996 The American Physical Society.

Excited states of the ${}_{}{}^{125}{}_{}{}^{}\mathrm{La}$ and ${}_{}{}^{127}{}_{}{}^{}\mathrm{La}$ nuclei were populated following ${}_{}{}^{112}{}_{}{}^{}\mathrm{Sn}$${(}^{16}$O,p2n) and ${}_{}{}^{112}{}_{}{}^{}\mathrm{Cd}$${(}^{19}$F,4n) fusion-evaporation reactions, respectively, and investigated using methods of in-beam γ-ray spectroscopy. Five collective bands in ${}_{}{}^{125}{}_{}{}^{}\mathrm{La}$, and eleven collective bands in ${}_{}{}^{127}{}_{}{}^{}\mathrm{La}$ were observed. The spin and/or parity assignments of excited states in these nuclei were based on angular-correlation and linear-polarization measurements. The experimental data are discussed and compared to the results of self-consistent total-Routhian-surface calculations including quadrupole pairing. © 1996 The American Physical Society.

The average magnetic moments of high spin states in Hf isotopes were determined in a transient field measurement at the 14 MV Koffler accelerator of the Weizmann Institute. The reaction ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$${(}^{40}$Ca,xn${)}^{166,165}$Hf at beam energies from 167 to 182.5 MeV was used to populate different high spin regions and provide the recoiling Hf nuclei with sufficient velocity to traverse the 2.9 mg/${\mathrm{cm}}^2$ Gd ferromagnetic layer. Standard double ratios and angular distributions for various low level transitions were measured to determine precession angles. These carry information regarding the average g factor of unobservable transitions at medium excitation. To obtain a more quantitative analysis regarding the time-decay history of the γ cascade, Monte Carlo simulations of the cascade were carried out. The significance of the results for understanding the single particle nature of these pre-yrast levels is discussed. © 1996 The American Physical Society.

Nuclear states in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, with an initial excitation energy E*=50 MeV, were populated via the isospin T=0 reaction ${}_{}{}^4{}_{}{}^{}\mathrm{He}$${+}^{24}$Mg and the mixed-isospin ${}_{}{}^3{}_{}{}^{}\mathrm{He}$${+}^{25}$Mg reaction. In both reactions the dilepton (${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$) and photon decay yields were measured concurrently, up to transition energies of 30 MeV. Both the dilepton and the photon yields are well described by a modified version of the statistical decay model, which includes both the photon and dilepton decays of giant resonances built on excited nuclear states. An excess of counts in the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ spectrum, over the converted photon yield, is observed in the energy region 17–22 MeV in the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ induced reaction, possibly indicating an entrance channel effect. © 1996 The American Physical Society.

A possibility to present the collective state wave functions of the triaxial rotor as multiple ‘‘Q excitations’’ built on the ground state is analyzed. It is shown that for arbitrary γ the wave functions of the low lying states of the ground and other bands are approximately pure multiple ‘‘Q excitation’’ states with an accuracy better than 75%. © 1996 The American Physical Society.

The Lipkin-Nogami method is generalized to deal with finite range density dependent forces. New expressions are derived and realistic calculations with the Gogny force are performed for the nuclei ${}_{}{}^{164}{}_{}{}^{}\mathrm{Er}$ and ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$. The sharp phase transition predicted by the mean field approximation is washed out by the Lipkin-Nogami approach. A much better agreement with the experimental data is reached with the new approach than with the Hartree-Fock-Bogoliubov one, especially at high spins. © 1996 The American Physical Society.

A microscopic Hamiltonian including realistic two-body interaction, is used to describe the single β Gamow-Teller transitions to the ground state, the first excited quadrupole state ($2_1^{+}$) and the two-quadrupole-phonon states ($0_{2\mathrm{-}\mathrm{ph}}^{+}$,$2_{2\mathrm{-}\mathrm{}\mathrm{ph}}^{+}$) of even-even isotopes ${}_{}{}^{118,120}{}_{}{}^{}\mathrm{Sn}$ from the two adjacent odd-odd nuclei ${}_{}{}^{118,120}{}_{}{}^{}\mathrm{In}$ and ${}_{}{}^{118,120}{}_{}{}^{}\mathrm{Sb}$. The higher-RPA effects are evaluated within a boson-expansion formalism. The transition amplitudes are studied as functions of the particle-particle interaction strength. The corresponding log${\mathit{ft}}_{\pm }$ values are also calculated and compared with experimental data as well as with the predictions of some previous calculations. The perturbative components of the states involved give important contribution to the transitions feeding the two-phonon states. Adding these, the agreement with the experimental data is improved. © 1996 The American Physical Society.

In shell model calculations for the yrast even-spin states of ${}_{}{}^{50}{}_{}{}^{}\mathrm{Cr}$, the static quadrupole moments of the low-spin states $2_1^{+}$, $4_1^{+}$, $6_1^{+}$, and $8_1^{+}$ are negative but those of the high-spin states ${10}_1^{+}$, ${12}_1^{+}$, and ${14}_1^{+}$ are positive. Yrast states with even spins greater than the single j shell limit, ${\mathit{J}}_{\max }$=14, again have negative quadrupole moments. © 1996 The American Physical Society.

Magnetic dipole transition matrix elements in superdeformed nuclei are calculated based on an axially symmetrically deformed Nilsson model. Several levels become the candidates to be assigned for the experimental evidence of the superdeformed band in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Hg}$ and ${}_{}{}^{193}{}_{}{}^{}\mathrm{Tl}$. Although the intrinsic ${\mathit{g}}_{\mathit{K}}$ factors for some levels show slower convergence to the asymptotic limit values, their wave functions show a good revival of L-S coupling scheme at superdeformation. Comparing the experimental data with the renormalized ${\mathit{g}}_{\mathit{K}}^{\prime }$, we find the pseudospin picture is not suitable for the superdeformed band. © 1996 The American Physical Society.

The fragmentation of one-nucleon knock-out strength at low energies is considered from the viewpoint of the two particle-one hole (and two hole- one particle) response propagator. The aim is to deal with particle-particle (and hole-hole) as well as particle-hole collectivity simultaneously. This is achieved on a Tamm-Dancoff level by the so-called Faddeev approximation of the 2p1h propagator. Results of this approach illustrate the relevance of this consistent treatment of both particle-particle (hole-hole) and particle-hole collectivity. A further extension, within the framework of 2p1h RPA which was sometimes applied in the past, has serious unsolved problems, some of which are discussed in detail. © 1996 The American Physical Society.

Properties of proton-rich nuclei at the sd-fp-shell boundary with 37≤A≤48 are investigated within the framework of the nuclear shell model. Predicted binding energies, one- and two-proton separation energies, and β-end-point energies are presented. Half-lives associated with one- and two-proton emissions are compared with β decay, and it is determined that the best candidates for the observation of correlated two-proton emission are ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ti}$ and ${}_{}{}^{45}{}_{}{}^{}\mathrm{Fe}$. The predicted branching ratios for β decay as a function of excitation energy in the daughter nucleus are shown. Where available, β-decay half-lives are compared with experiment and are found to be in overall good agreement. © 1996 The American Physical Society.

Evaporation residues (ER) of Z=34–43 are measured in singles and in coincidence with emitted protons, deuterons, tritons, and alpha particles. Measurements are done with a large detector array that covers the scattering angles from 2.5° to 25°. The energy centroids of the coincidence spectra of the protons are reasonably well described by statistical model calculations assuming complete fusion, although those for the deuterons and tritons are not. The α-particle spectra are significantly different than the calculated ones. The slopes of the high energy spectra of the protons required a level density parameter a≳A/12. Comparisons between the experimental ER singles spectra and complete fusion calculations show small deviations that can be explained by incomplete fusion however, when analyzed in coincidence with light particles a very good description with complete fusion is found especially if the emission of intermediate mass fragments is included in the calculations. © 1996 The American Physical Society.

Inclusive inelastic scattering (n,n′x) continuum cross sections have been measured at 65 MeV for Fe, Sn, and Pb targets using a detection system consisting of large area wire chambers and ΔE⋅E scintillation detectors in conjunction with a ${\mathrm{CH}}_2$ n-p converter. The continuum (n,n′x) spectra are compared with earlier (p,p′x) data, and comparisons with cascade-statistical and preequilibrium continuum models are also made. © 1996 The American Physical Society.

Differential cross sections for evaporation residues and fission fragments for 35A, 100A, 130A and 155A MeV ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ on targets ranging from ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$ to ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ have been measured. The angle-integrated cross sections are larger than what might be expected. The fission fragment-fission fragment folding angle correlations for 35A, 100A MeV ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ and 25A MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ on similar targets were also measured. The average linear momentum transfer has been deduced from both the fission angle correlation and from the fore-aft asymmetry of the fission angular distributions in the laboratory system. The data are all consistent with a picture where pre-equilibrium particle emission removes an increasing fraction of the orbital angular momentum as the bombarding energy increases. This allows a large range of partial waves to contribute to formation of a composite nucleus with a finite fission barrier. © 1996 The American Physical Society.