A Skyrme-type Lagrangian for a skyrmion imbedded in nuclear matter is proposed. The dependence of the static nucleon properties and the nucleon-nucleon tensor interaction on nuclear density is investigated.

We calculate the radiative decay widths of decuplet hyperons in a chiral constituent quark model including electromagnetic exchange currents between quarks. Exchange currents contribute significantly to the $E2\mathrm{}$ transition amplitude, while they largely cancel for the $M1\mathrm{}$ transition amplitude. Strangeness suppression of the radiative hyperon decays is found to be weakened by exchange currents. Differences and similarities between our results and other recent model predictions are discussed.

We perform an expansion of the virtual Compton scattering amplitude for low energies and low momenta and show that this expansion covers the transition from the regime to be investigated in the scheduled photon electroproduction experiments to the real Compton scattering regime. We discuss the relation of the generalized polarizabilities of virtual Compton scattering to the polarizabilities of real Compton scattering.

We calculate the chiral and thermal susceptibilities for two confining Dyson-Schwinger equation models of QCD with two light flavors, a quantitative analysis of which yields the critical exponents $\beta$ and $\delta$ that characterize the second-order chiral symmetry restoration transition. The method itself is of interest, minimizing the influence of numerical noise in the calculation of the order parameter for chiral symmetry breaking near the critical temperature. For the more realistic of the two models we estimate $T_c\approx 153\hspace{0.5em}$MeV and the non-mean-field values $\beta =0.46\mathrm{}\pm 0.04$, $\delta =4.3\mathrm{}\pm 0.3$, and $1/\left(\beta \delta \right)=0.54\mathrm{}\pm 0.05$, which we discuss in comparison with the results of other models.

We report measurements of the photon rates and energy spectra from inclusive radiative muon capture on three nickel isotopes using a photon pair spectrometer at the TRIUMF cyclotron. The values of $R_{\gamma },$ the partial branching ratios of radiative muon capture for photon energies $>57\mathrm{}$ MeV, for ${}^{58,60,62}\mathrm{Ni}$ were found to be (in units of ${10}^{-5})$ $1.48\pm 0.08,$ $1.39\pm 0.09,$ and $1.05\pm 0.06,$ assuming a Fermi-gas photon spectral shape. The results reveal a significant isotope effect in the nickel branching ratios and a simple empirical scaling of the present nickel and earlier nuclear $R_{\gamma }$ data with neutron excess. Furthermore, the observed atomic mass and neutron excess dependence of the entire nuclear $R_{\gamma }$ data set is well reproduced by a relativistic Fermi-gas calculation. The ability of the model to reproduce the variation of the $R_{\gamma }$ data using the Goldberger-Treiman formula for $g_p$ suggests there is no compelling reason to invoke a more exotic $A$-dependent renormalization of $g_p.$

Coherent pion photoproduction on the deuteron is studied in the threshold region spanning photon lab energies from threshold at 139.83 MeV to 160 MeV. Unlike previous similar calculations which used the now obsolete value for the $s$-wave $E_{0+}$ multipole, our work relies on the latest information on the elementary amplitudes which are in excellent agreement with recent precise data on the $\gamma \overrightarrow{p}{\pi }^{0}p$ reaction. We compare the exact treatment of pion propagation against various approximations often used in the literature and their impact on the very important pion rescattering contribution. We have investigated the sensitivity of the $\gamma \overrightarrow{D}{\pi }^{0}D$ cross section to various choices of the values of the elementary multipoles and in particular the neutron $s$-wave amplitude $E_{0+}^{{\pi }^{0}n}.$ The Fermi motion, corrections due to the boost from the nucleon to the deuteron frames as well as the deuteron $D$-state are all taken into account. The predicted total and differential cross sections are compared with the very recent experimental data from the Saskatchewan Accelerator Laboratory.

The existence of a low energetic intermediate state (IS) in ${}^{180}\mathrm{Ta}$ which provides a coupling of the stable isomer and the radioactive ground state was investigated by means of Coulomb excitation. Natural tantalum foils were irradiated by protons with incident energies between 3.0 and 3.7 MeV, and with $\alpha$ particles in the energy range $12-20\hspace{0.5em}\mathrm{MeV}.$ Subsequently, the foils were counted for the induced ground state activity of ${}^{180}\mathrm{Ta}.$ From the thick target yields an IS between 0.6 and 2.2 MeV excitation energy was inferred. The population of the IS in the stellar environment of the $s$ process depends critically on the prevailing temperatures. Current stellar models suggest $s$-process temperatures below $3.1\times {10}^8\hspace{0.5em}\mathrm{K}$ which lead to a negligible population of intermediate states above 1.2 MeV. Thus, the present data do not allow stringent conclusions about the destruction of ${}^{180}\mathrm{Ta}$ under these conditions, but an $s$ process origin seems still possible. Furthermore, the experiments support the existence of a new isomer in ${}^{184}\mathrm{Re}.$

Updated stellar rates for the reaction ${}^{23}\mathrm{Mg}(p,\gamma {)}^{24}\mathrm{Al}$ are calculated by using all available experimental information on ${}^{24}\mathrm{Al}$ excitation energies. Proton and $\gamma$-ray partial widths for astrophysically important resonances are derived from shell-model calculations. Correspondences of experimentally observed ${}^{24}\mathrm{Al}$ levels with shell-model states are based on application of the isobaric multiplet mass equation. Our new rates suggest that the ${}^{23}\mathrm{Mg}(p,\gamma {)}^{24}\mathrm{Al}$ reaction influences the nucleosynthesis in the mass $A>\mathrm{}20\mathrm{}$ region during thermonuclear runaways on massive white dwarfs.

Properties of dense nucleon matter and the structure of neutron stars are studied using variational chain summation methods and the new Argonne $v_{18}$ two-nucleon interaction, which provides an excellent fit to all of the nucleon-nucleon scattering data in the Nijmegen database. The neutron star gravitational mass limit obtained with this interaction is 1.67$M_{\odot }.$ Boost corrections to the two-nucleon interaction, which give the leading relativistic effect of order ${\mathrm{}(v/c)\mathrm{}}^2,$ as well as three-nucleon interactions, are also included in the nuclear Hamiltonian. Their successive addition increases the mass limit to 1.80 and 2.20 $M_{\odot }.$ Hamiltonians including a three-nucleon interaction predict a transition in neutron star matter to a phase with neutral pion condensation at a baryon number density of $\sim 0.2\hspace{0.5em}{\mathrm{fm}}^{-3}.$ Neutron stars predicted by these Hamiltonians have a layer with a thickness on the order of tens of meters, over which the density changes rapidly from that of the normal to the condensed phase. The material in this thin layer is a mixture of the two phases. We also investigate the possibility of dense nucleon matter having an admixture of quark matter, described using the bag model equation of state. Neutron stars of 1.4$M_{\odot }$ do not appear to have quark matter admixtures in their cores. However, the heaviest stars are predicted to have cores consisting of a quark and nucleon matter mixture. These admixtures reduce the maximum mass of neutron stars from 2.20 to 2.02 (1.91) $M_{\odot }$ for bag constant $B=200\mathrm{}\hspace{0.5em}\mathrm{}\left(122\right)\mathrm{}\hspace{0.5em}{\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{f}\mathrm{m}}^3.$ Stars with pure quark matter in their cores are found to be unstable. We also consider the possibility that matter is maximally incompressible above an assumed density, and show that realistic models of nuclear forces limit the maximum mass of neutron stars to be below 2.5$M_{\odot }.$ The effects of the phase transitions on the composition of neutron star matter and its adiabatic index $\Gamma$ are discussed.

Electron-γ directional correlation measurements have been done in ${}^{134}\mathrm{Ba}$ for the first time using an apparatus including cooled Si surface barrier detector for the electrons and HPGe for the γ’s. Experimental particle parameters for pure intense E2 transitions have been calculated from γγ and electron-γ results, giving $b_2\mathrm{}\left(605K\right)=1.31\mathrm{}\left(28\right)\mathrm{}$ and $b_2\mathrm{}\left(795K\right)=1.20\mathrm{}\left(23\right).$ Some mixed transitions were also analyzed. The $326K$ electron conversion ratio ${\alpha }_{326K}=14\mathrm{}\left(6\right)\mathrm{}\times {10}^{-2}$ was measured. An upper bound for the E0/E2 mixing ratio was estimated to the $2^{+\prime }\to 2^{+}(563\mathrm{}$ keV) transition by the $e\gamma$ interference E0/E2 method, giving $q_K^2\mathrm{}(E0/E2\mathrm{})\mathrm{}<~\mathrm{0.06.}$

High-spin states in ${}^{113}\mathrm{Sb}$ have been investigated by in-beam γ-ray spectroscopy with the ${}^{103}{\mathrm{R}\mathrm{h}(}^{16}\mathrm{O},\alpha 2n)$ and ${}^{88}\mathrm{Sr}{(}^{28}\mathrm{Si},p2n)$ reactions at beam energies of 80 and 120 MeV, respectively. Two $\Delta I=1\mathrm{}$ strongly coupled rotational bands were observed; one is a positive parity band that gains approximately 8ħ in spin alignments as a result of the level crossing at $ħ\omega \sim 0.4$ MeV and the other is a negative parity band that shows no evidence of a level crossing below $ħ\omega =0.48\mathrm{}$ MeV. This negative-parity band has spin alignment of $7ħ,$ and is interpreted as intruder states of a $2p-1h$ $\pi [{(g}_{7/2}{)}^2\otimes {(g}_{9/2}{)}^{-1}]$ structure coupled to the two-quasineutron $7^{-}$ state of the ${}^{112}\mathrm{Sn}$ core. The previously observed decoupled rotational band involving $2p-2h$ excitations across the shell gap has been also confirmed.

Excited states in ${}^{181}\mathrm{Ta}$ have been identified using time-correlated $\gamma$-ray spectroscopy and particle-$\gamma$ techniques following the incomplete fusion reaction ${}^{176}\mathrm{Yb}{(}^{11}\mathrm{B},\alpha {2n)}^{181}\mathrm{Ta}.$ As well as observing the rotational band based on the 11 ns isomer at 482 keV from the ${5/2}^{+}\left[402\right]$ proton configuration, which is found to be essentially identical to that associated with its ${7/2}^{+}\left[404\right]$ pseudospin partner, several multi-quasiparticle isomers are observed including a $33\hspace{0.5em}\mu \mathrm{s}$ state, of probable spin and parity ${21/2}^{-},$ at 1483 keV. Experimental states are compared with multi-quasiparticle calculations.

The dynamical effects of ground state correlations for excitation energies and transition strengths near the superfluid phase transition are studied in the soluble two level pairing model, in the context of the particle-particle self-consistent random phase approximation (SCRPA). Exact results are well reproduced across the transition region, beyond the collapse of the standard particle-particle random phase approximation. The effects of two-body correlation in the SCRPA are displayed explicitly.

We describe the mixing of the $q\overline{q}$ pseudoscalar channel with the longitudinal $q\overline{q}$ axial-vector channel, making use of a generalized Nambu–Jona-Lasino model that includes a model of confinement. In addition to the pion, we find $J^P{=0\mathrm{}}^{-}$ states at 1.18, 1.36, 1.47, 1.63, and 1.68 GeV. The first three of these states are in the region of the π(1300) excitation that is assigned a mass of $1300\pm 100\mathrm{MeV}$ and a width of 200–600 MeV in the data tables. Our work, therefore, suggests the π(1300) may not represent a single state of $q\overline{q}$ character.

The excitation energy systematics of $\pi h_{11/2}\otimes \nu h_{11/2}$ yrast bands of odd-odd isotopes ${}^{118–132}\mathrm{Cs}$ are studied, and as a result of this study we suggest that the spin values of lowest observed states of yrast bands of ${}^{118,122,124,126,128}\mathrm{Cs}$ be reassigned as 8, 9, 9, 9, and 10, respectively. These new spin assignments are also supported by the argument of alignment additivity.

The renormalized elastic ππ scattering amplitude to one loop is calculated in the chiral limit in the σ model and in a quantum hadrodynamic model (QHD-III) with vector mesons. It is argued that QHD-III reduces to the linear σ model in the limit that the vector meson masses become large. The pion decay constant is also calculated to 1-loop in the σ model, and at tree level in QHD-III; it is shown that the coefficient of the tree level term in the scattering amplitude equals $F_{\pi }^{-2}.$ The 1-loop correction of $F_{\pi }$ in QHD-III violates strong isospin current conservation. Thus, it is concluded that QHD-III can, at best, only describe the strongly interacting nuclear sector.

Lifetimes of levels in two doubly-decoupled bands of ${}^{134}\mathrm{Pr}$ involving neutron intruder orbits have been measured using Doppler-shift techniques. The deduced transition quadrupole moments are consistent with total Routhian surface predictions for the suggested configurations of both bands. The negative-parity band with one neutron in the $i_{13/2}$ orbit has a much larger quadrupole deformation than the positive-parity band with a neutron in the ${(f}_{7/2}{/h}_{9/2})$ orbit, reflecting the strong polarizing effect of the $N=6\mathrm{}$ intruder orbit on the nuclear shape.

The charge-moment technique has been used to study the fragment charge distribution for the ${}^3{\mathrm{H}\mathrm{e}\left(4.8\mathrm{}\mathrm{}\mathrm{G}\mathrm{e}\mathrm{V}\right)+}^{197}\mathrm{Au}$ reaction. A large variety of fragment charges characterized by a relative variance $\sim 2.3,$ is observed for excitation energies around 5.5 MeV/nucleon. Similar signals related to a phase transition are predicted by the percolation model and the statistical multifragmentation model. Effects of detector acceptance and contribution from fission are discussed.

Complete statistical model calculations including temperature- and spin-dependent theoretical strength functions of the giant dipole resonance (GDR) have been performed for the decay of excited ${}^{120}\mathrm{Sn}$ for the first time. Previous analyses of GDR data with theoretical models compared the centroid and full width at half maximum of the theoretical strength functions with the extracted GDR parameters. In the new approach presented, the entire shape of the strength functions is considered and the theoretical spectra obtained can be directly compared with the experiment. This analysis does not rely on the accuracy of extracting the GDR parameters and/or the nuclear temperature of one data point. The nature of the temperature dependence of the GDR in the hot ${}^{120}\mathrm{Sn}$ nucleus within the thermal fluctuation and collisional damping model is discussed in this new perspective.

An attractive, energy-dependent mean-field potential for baryons is introduced in order to generate a soft region in the nuclear equation of state, as suggested by recent lattice QCD calculations of baryon-free matter at finite temperature. Based on a hadronic transport model, we find that although this equation of state has negligible effects on the inclusive hadronic spectra, it leads to a minimum in the energy dependence of the transverse collective flow and a delayed expansion of the compressed matter. In particular, the transverse flow changes its direction as the colliding system passes through the softest region in the equation of state.