High-spin states have been studied in neutron-deficient ${}_{}{}^{132}{}_{}{}^{}\mathrm{Nd}$, produced in the ${}_{}{}^{105}{}_{}{}^{}\mathrm{Pd}({}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}, \alpha p3n\gamma )$ reaction, using the Gammasphere $\gamma$-ray spectrometer in conjunction with the Microball charged-particle detector array, Three new, weakly populated rotational bands have been found, which are believed to be associated with a superdeformed (second minimum) prolate shape. Comparison of the properties of these bands with Woods-Saxon cranking calculations suggests that they are built upon negative-parity neutron configurations that involve only one intruder orbital ($\nu i_{\frac{13}{2}}$) from the $N=6\mathrm{}$ shell. One of the bands has been linked into the normally deformed states allowing an estimation of the spin, parity, and excitation energy of the band.

Fragment production has been studied as a function of the source mass and excitation energy in peripheral collisions of ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$+${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ at 43 MeV/nucleon and ${}_{}{}^{70}{}_{}{}^{}\mathrm{Ge}$+${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ti}$ at 35 MeV/nucleon. The results are compared to the Au+Au data at 600 MeV/nucleon obtained by the ALADIN Collaboration. A mass scaling, by $A_{\mathrm{source}}\sim 35 \mathrm{and} 190$, strongly correlated to excitation energy per nucleon, is presented, suggesting a thermal fragment production mechanism. Comparisons to a standard sequential decay model and the lattice-gas model are made. Fragment emission from a hot, rotating source is unable to reproduce the experimental source size scaling.

Fission fragment anisotropies have been measured to energies extending well above the barrier for three entrance channels leading to the same compound nucleus ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cf}$. For the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ systems, lying on either side of the Businaro-Gallone critical asymmetry, the mean square angular momentum is matched at an excitation energy of 62 MeV. The anisotropies, although different at lower energies, are in agreement within experimental errors at this excitation energy and thus show no entrance channel dependence.

Measurements of polarized-neutron–polarized${\mathrm{-}}^3$He scattering are reported. The target consisted of cryogenically polarized solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, with thickness 0.04 atom/b and polarization ∼0.4. Polarized neutrons were produced via the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$(p→,n→${)}^3$He or ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(d→,n→${)}^3$He polarization-transfer reactions. The longitudinal and transverse total cross-section differences Δ${\mathrm{\sigma }}_{\mathit{L}}$ and Δ${\mathrm{\sigma }}_{\mathit{T}}$ were measured for incident neutron energies 2–8 MeV. The results are compared to phase-shift predictions based on four different analyses of n${\mathrm{-}}^3$He scattering. The best agreement is obtained with a recent R-matrix analysis of A=4 scattering and reaction data, lending strong support to the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ level scheme obtained in that analysis. Discrepancies with other phase-shift parametrizations of n${\mathrm{-}}^3$He scattering exist, attributable in most instances to one or two particular partial waves. © 1996 The American Physical Society.

We make use of a momentum-space bosonization of a generalized Nambu–Jona-Lasinio model to calculate the contribution of rho and omega exchange to the one-boson-exchange (OBE) model of the nucleon-nucleon interaction. Momentum-dependent meson-quark coupling constants are obtained in the bosonization scheme. A vector-meson-dominance (VMD) model is used to obtain information concerning the momentum dependence of the meson-nucleon vertex, other than that which arises from the momentum dependence of the meson-quark coupling constants. We find good agreement with the magnitude of the force at ${\mathit{q}}^2$=0 for both rho and omega exchange. The momentum dependence of the interaction in the region -0.2 ${\mathrm{GeV}}^2$≤${\mathit{q}}^2$≤0 was calculated. We only obtain about two-thirds of the strength of the OBE interaction at ${\mathit{q}}^2$=-0.2 ${\mathrm{GeV}}^2$, suggesting the importance of interactions of shorter range than that considered here. (We note that, for -0.2 ${\mathrm{GeV}}^2$≤${\mathit{q}}^2$≤0, we span the range of ${\mathit{q}}^2$ of significance for nuclear structure studies.) © 1996 The American Physical Society.

We study the use of the Okubo method for constructing effective two-particle, instant form and front form, one-particle exchange models, starting from quantum field theory vertices. The truncation of the field theory that is made in applying the Okubo method leads to mass operators that are not exactly Poincaré invariant. It is found that when the spurious terms that destroy the exact Poincaré invariance are eliminated the instant and front form potentials come out essentially the same, however they wind up in slightly different two-particle Lippmann-Schwinger equations. In order to study the practical consequences of this difference, a numerical comparison is made between instant and front form one-meson-exchange models of the two-nucleon system that have been fit to the same partial-wave analysis of the two-nucleon data. These models assume the exchange of π, η, ρ, ω, δ, and σ mesons. No dramatic differences are found between the instant form and front form vertex parameters obtained from the fits. © 1996 The American Physical Society.

First, a systematic procedure is derived for obtaining three-dimensional bound-state equations from four-dimensional ones. Unlike ‘‘quasipotential approaches’’ this procedure does not involve the use of delta-function constraints on the relative four-momentum. In the absence of negative-energy states, the kernels of the three-dimensional equations derived by this technique may be represented as sums of time-ordered perturbation theory diagrams. Consequently, such equations have two major advantages over quasipotential equations: They may easily be written down in any Lorentz frame, and they include the meson-retardation effects present in the original four-dimensional equation. Second, a simple four-dimensional equation with the correct one-body limit is obtained by a reorganization of the generalized ladder Bethe-Salpeter kernel. Third, our approach to deriving three-dimensional equations is applied to this four-dimensional equation, thus yielding a retarded interaction for use in the three-dimensional bound-state equation of Wallace and Mandelzweig. The resulting three-dimensional equation has the correct one-body limit and may be systematically improved upon. The quality of the three-dimensional equation, and our general technique for deriving such equations, is then tested by calculating bound-state properties in a scalar field theory using six different bound-state equations. It is found that equations obtained using the method espoused here approximate the wave functions obtained from their parent four-dimensional equations significantly better than the corresponding quasipotential equations do. © 1996 The American Physical Society.

A three-body calculation of the electromagnetic observables of the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ ground state is reported. The nucleus of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ is considered as a three-body system of one neutral plus two charged particles: n+α+α. Simple two-body n-α and α-α potentials, plus Coulomb, constitute the only input to the momentum-space three-body equations. No adjustable parameters are used. The equations are solved numerically for the ground state, generating simultaneously the binding energy and wave function. The normalized wave function is then used in the calculation of the matrix elements of the electromagnetic operators. The neutron and alpha particle form factors are folded in this calculation. Results are presented for ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ elastic longitudinal and transverse form factors, and static multipole moments: rms charge radius, electric quadrupole moment, and magnetic dipole and octupole moments. © 1996 The American Physical Society.

Correlated hyperspherical harmonics wave functions with Δ-isobar admixtures obtained from realistic interactions are used to study the thermal neutron radiative capture on deuterium, and the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(p→,γ${)}^3$He and p(d→,γ${)}^3$He reactions in the center of mass energy range 0–100 keV. The nuclear electromagnetic current includes one- and two-body components. Results for the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(n→,γ${)}^3$H cross section and photon polarization parameter, as well as for the energy dependence of the astrophysical factor and angular distributions of the differential cross section, vector and tensor analyzing powers, and photon linear polarization coefficient of the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(p→,γ${)}^3$He and p(d→,γ${)}^3$He reactions are reported. Large effects due to two-body currents, in particular the long-range ones associated with the tensor component of the nucleon-nucleon interaction, are observed in the photon polarization parameter and vector analyzing power. Good, quantitative agreement between theory and experiment is found for all observables, with the exception of the vector analyzing power for which the calculated values underestimate the data by about 30%. © 1996 The American Physical Society.

The magnetic hyperfine splitting frequencies of (i) ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$ in Fe ${(}^{57}$NiFe), (ii) ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$ in Ni ${(}^{57}$NiNi), and (iii) ${}_{}{}^{59}{}_{}{}^{}\mathrm{Fe}$ in Fe ${(}^{59}$FeFe) were measured with the technique of nuclear magnetic resonance on oriented nuclei (NMR-ON) at low temperatures. The NMR-ON spectra were observed by detecting the β-ray asymmetries. The resonance frequencies at zero external magnetic field were deduced from the extrapolation of the external field dependence of the resonance frequencies: ν${(}^{57}$NiFe)=94.23(2) MHz, ν${(}^{57}$NiNi)=30.02(4) MHz, and ν${(}^{59}$FeFe)=57.719(11) MHz. With the known hyperfine fields of ${\mathit{B}}_{\mathrm{HF}}$(NiNi)=-7.406(8) T and ${\mathit{B}}_{\mathrm{HF}}$(FeFe)=-33.82(3) T, the magnetic moments of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Fe}$ were determined to be μ${(}^{57}$Ni)=-0.7975(14)${\mathrm{\mu }}_{\mathit{N}}$ and μ${(}^{59}$Fe)=-0.3358(4)${\mathrm{\mu }}_{\mathit{N}}$. The precise value of the hyperfine field of ${\mathit{B}}_{\mathrm{HF}}$${(}^{57}$NiFe) was also deduced as -23.25(5) T. The measured values of the magnetic moment are compared with those based on the shell model. © 1996 The American Physical Society.

Superdeformed (SD) states of ${}_{}{}^{190}{}_{}{}^{}\mathrm{Hg}$ have been studied with the Eurogam Phase 2 γ-ray spectrometer using the ${}_{}{}^{160}{}_{}{}^{}\mathrm{Gd}$${(}^{34}$S,4n) reaction. Two new excited SD bands have been found and identified as belonging to this nucleus, bringing the total number of SD bands in ${}_{}{}^{190}{}_{}{}^{}\mathrm{Hg}$ to 4. One of the new bands has a dynamic moment of inertia that is very similar to that of the yrast SD band of ${}_{}{}^{190}{}_{}{}^{}\mathrm{Hg}$ and most other SD bands in the A∼190 region. In contrast, the other band has a dynamic moment of inertia which is mainly constant as a function of rotational frequency and exhibits a dramatic increase at the lowest frequencies. The observed dynamic moments of inertia are compared with the results of random phase approximation calculations based on the cranked shell model. Finally, the known excited SD band has been extended towards lower frequencies and new transitions have been found linking this band to the yrast SD band. The extracted B(E1) values of the new linking transitions give further support for the possible octupole vibrational character of this band. © 1996 The American Physical Society.

The γ transitions in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Ba}$, ${}_{}{}^{149}{}_{}{}^{}\mathrm{Ce}$, and ${}_{}{}^{151,153}{}_{}{}^{}\mathrm{Nd}$ have been identified from γ-γ-γ, γ-γ, x-γ, and x-γ-γ coincidence studies of spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$. The yrast positive parity band in ${}_{}{}^{149}{}_{}{}^{}\mathrm{Ce}$ is assigned to an ${\mathit{i}}_{13/2}$, neutron favored signature. The yrast negative parity band in ${}_{}{}^{149}{}_{}{}^{}\mathrm{Ce}$ is assigned a ${\mathit{h}}_{9/2}$ proton favored signature. The positive parity band in ${}_{}{}^{151}{}_{}{}^{}\mathrm{Nd}$ corresponds to the positive parity band in ${}_{}{}^{149}{}_{}{}^{}\mathrm{Ce}$. The negative parity band in ${}_{}{}^{153}{}_{}{}^{}\mathrm{Nd}$ corresponds to the negative parity bands of ${}_{}{}^{149}{}_{}{}^{}\mathrm{Ce}$ and ${}_{}{}^{161}{}_{}{}^{}\mathrm{Er}$. The band observed in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Ba}$ is built on the ${\mathit{h}}_{9/2}$ orbital. The plots for ${\mathit{J}}_1$ in these isotopes are remarkably similar, supporting our assignments. © 1996 The American Physical Society.

In an experiment at the LISE3 facility of GANIL, we produced the proton-rich isotope ${}_{}{}^{22}{}_{}{}^{}\mathrm{Si}$ by the fragmentation of a ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ primary beam at 95 MeV/nucleon. After implantation in a detector telescope, we studied the decay of ${}_{}{}^{22}{}_{}{}^{}\mathrm{Si}$ via a measurement of charged particles emitted during the decay. The most important β-delayed proton activity is observed at an energy of ${\mathit{E}}_{\mathit{p}}$ = (1.99±0.05) MeV with a branching ratio of (20±2)%. The spectra allow us also to determine the half-life of ${}_{}{}^{22}{}_{}{}^{}\mathrm{Si}$ to be ${\mathit{T}}_{1/2}$ = (29±2) ms. These results are compared with theoretical estimates and model predictions. © 1996 The American Physical Society.

The nuclear structure of ${}_{}{}^{97}{}_{}{}^{}\mathrm{Tc}$ was studied using the ${}_{}{}^{96}{}_{}{}^{}\mathrm{Mo}$${(}^3$He,pnγ) reaction, which has populated most states in the nucleus below 2 MeV excitation energy. The proton exit channel was isolated from competing reaction channels by operating γ-ray detectors in coincidence with a large-solid-angle proton detector. The experiments included γ-ray excitation functions, γ-ray angular distributions, and γ-γ coincidences. The results were interpreted using a particle-rotor model. © 1996 The American Physical Society.

High-lying excitations were studied by means of the ${}_{}{}^{207}{}_{}{}^{}\to _{}^{208}{}_{}{}^{}$Pb, ${}_{}{}^{209}{}_{}{}^{}\to _{}^{210}{}_{}{}^{}$Bi, and ${}_{}{}^{59}{}_{}{}^{}\to _{}^{60}{}_{}{}^{}$Ni stripping reactions and ${}_{}{}^{209}{}_{}{}^{}\to _{}^{208}{}_{}{}^{}$Pb and ${}_{}{}^{63}{}_{}{}^{}\to _{}^{62}{}_{}{}^{}$Ni pickup reactions induced by ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ projectiles at 48 and 42 MeV/nucleon, respectively. In the stripping spectra, structures a few MeV wide are observed at excitation energies of 10–15 MeV, embedded in a large continuum. The corresponding Q values suggest that these structures are predominantly due to single-particle excitations rather than to the excitation of collective states such as giant resonances. This interpretation is in agreement with a microscopic calculation showing that in the one-nucleon transfer reactions only a small part of the cross section is due to the collective excitations. The overall shape of the neutron stripping spectra is well reproduced by the semiclassical reaction model of Bonaccorso and Brink, which treats on the same footing both the breakup of the projectile and the transfer to single-particle resonances. © 1996 The American Physical Society.

Gamow-Teller ($1^{+}$) strength was studied in ${}_{}{}^{38}{}_{}{}^{}\mathrm{K}$ with the analog reactions ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ar}$(p,n${)}^{38}$K and ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ca}$(${\mathrm{\beta }}^{+}$${)}^{38}$K. The (p,n) reaction was performed at 135 MeV using the beam swinger facility at the Indiana University Cyclotron Facility. Excitation-energy spectra were measured at 15 angles between 0° and 63°. Neutron energies were measured by the time-of-flight method using a large-volume plastic scintillator array at a flight path of 131.0 m. The overall energy resolution was 280 keV. Gamow-Teller (GT) strength was extracted from the measured angular distributions to discrete $1^{+}$ final states. The β-decay experiment was performed with the ISOLDE on-line mass separator facility at CERN. The β-decay branching ratios were determined by observing the delayed γ decays of ${}_{}{}^{38}{}_{}{}^{}\mathrm{K}$. These decay measurements provide an increased sensitivity over earlier measurements and are able to extract transitions down to ∼ ${10}^{\mathrm{-}4}$ of the strongest branches. The B(GT) values obtained from the two experiments are generally in good agreement, except for the transition to the first $1^{+}$ state at 0.46 MeV, which is observed to be much weaker in the (p,n) measurements. The β-decay measurements provide good resolution and high sensitivity while the (p,n) measurements extend the β-decay measurements to higher excitation energies. The summed B(GT) strength is ∼50% of the simple Ikeda sum rule. The distribution of GT strength is in reasonable agreement with that predicted from a shell-model calculation using ‘‘effective’’ GT operators. © 1996 The American Physical Society.

An experiment performed on the early implementation of the GAMMASPHERE array to populate the high-spin states in ${}_{}{}^{133}{}_{}{}^{}\mathrm{Ce}$ has revealed the presence of several rotational structures with energy spacings of Δ${\mathit{E}}_{\gamma }$∼100 keV. Some of these bands exhibit a backbend at ħω∼0.6 MeV and are observed to high rotational frequencies—ħω∼0.85 MeV. These characteristics are very different from those observed for any other rotational bands in this mass region. The properties of these new structures will be discussed within the framework of cranked Strutinsky-Woods-Saxon calculations. Currently, these bands are thought to be based on triaxial nuclear shapes. © 1996 The American Physical Society.

In bombardments of ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}$ with ${}_{}{}^{34}{}_{}{}^{}\mathrm{S}$ we discovered the α-decaying nuclide ${}_{}{}^{273}{}_{}{}^{}110$. We conducted an extensive off-line search of the raw data for event sequences which fit the expected pattern of implantation in a position-sensitive detector and subsequent decay of ${}_{}{}^{273}{}_{}{}^{}110$ and its descendants. We observed one three-member sequence of genetically linked α decays, resulting in ${\mathit{E}}_{\mathrm{\alpha }}$=11.35 MeV, a half-life of 0.$3_{\mathrm{-}0.2}^{+1.3\mathrm{}}$ ms, and a production cross section of about 0.4 pb for ${}_{}{}^{273}{}_{}{}^{}110$. Other possible ${}_{}{}^{273}{}_{}{}^{}110$ event chains were also observed. The measured α-particle energy for the N=163 nuclide ${}_{}{}^{273}{}_{}{}^{}110$ provides direct evidence for a neutron shell closure at N=162. © 1996 The American Physical Society.

High-spin states in ${}_{}{}^{78}{}_{}{}^{}\mathrm{Br}$ have been studied up to an excitation energy of approximately 6 MeV and a spin of 17ħ using the ${}_{}{}^{70}{}_{}{}^{}\mathrm{Zn}$${(}^{11}$B,3n${)}^{78}$Br reaction at a beam energy of 45 MeV. The properties of the observed rotational bands, including moments of inertia, signature splitting, and signature inversion, are discussed within the context of the cranked shell model. It is shown that cranked-shell-model calculations are able to reproduce the experimentally observed signature inversion in the positive-parity yrast bands in the odd-odd isotopes ${}_{}{}^{74,76,78}{}_{}{}^{}\mathrm{Br}$, which permits the assignments of quasiparticle configurations to these bands. © 1996 The American Physical Society.

In two previous papers, the Kerman-Klein-Dönau-Frauendorf model was used to study rotational bands of odd deformed nuclei. Here we describe backbending for odd nuclei using the same model. The backbending in the neighboring even nuclei is described by a phenomenological two-band model, and this core is then coupled to a large single-particle space, as in our previous work. The results obtained for energies and M1 transition rates are compared with experimental data for ${}_{}{}^{165}{}_{}{}^{}\mathrm{Lu}$ and for energies alone to the experimental data for ${}_{}{}^{179}{}_{}{}^{}\mathrm{W}$. For the case of ${}_{}{}^{165}{}_{}{}^{}\mathrm{Lu}$ comparison is also made with previous theoretical work. © 1996 The American Physical Society.