We use a boost-invariant one-dimensional (cylindrically symmetric) fluid dynamics code to calculate thermal photon production in the central rapidity region of S+Au and Pb+Pb collisions at SPS energy (√s =20 GeV/nucleon). We assume that the hot matter is in thermal equilibrium throughout the expansion, but consider deviations from chemical equilibrium in the high temperature (deconfined) phase. We use equations of state with a first-order phase transition between a massless pion gas and quark gluon plasma, with transition temperatures in the range 150≤${\mathit{T}}_{\mathit{c}}$≤200 MeV.

Pion multiplicity and energy spectrum in medium energy heavy-ion collisions are analyzed in a model with spherical expansion, resonance decay contribution, and chemical nonequilibrium effects. fitting the data for central La+La collision at ${\mathit{E}}_{\mathrm{lab}}$=1.35 GeV/nucleon we find that the physically reasonable freeze-out conditions require a strong collective motion to describe the pion spectrum and a positive value of pion chemical potential to fit the total pion multiplicity. The data do not lend to conclusive evidence on the presence of Δ resonance at the freeze-out.

Possible existence of various collective modes, such as the compressional, the polarizational, and the surface vibrational modes in a strangelet, are discussed in the framework of hydrodynamic model. The eigenenergies of these collective modes are estimated using an equation of state for the interacting quark matter based on the quark bag model and are compared with the corresponding modes in the nuclei. It is found that, within the uncertainties associated with the bag model parameters, the collective eigenenergies in a strangelet are 1.5–4 times higher than those in the nuclei of same baryon number. The collective mode behavior may distinguish a strangelet from a large nucleus and give signature of the formation of quark-gluon plasma in ultrarelativistic heavy-ion collision experiments.

The spin-orbit interaction coming from the scalar meson-exchange potential between quarks is included in a quark cluster model for the nucleon-nucleon interaction. Its influence on the triplet P-wave scattering phase shifts and on the baryon spectrum is analyzed. We require that the deuteron binding energy is simultaneously reproduced. Our results indicate that a considerable part of the nucleon-nucleon spin-orbit force can be explained by gluon and sigma exchange between quarks while improving the description of the excited baryon spectrum.

The QCD sum rule method is applied to derive a formula for the ρ, ω, and φ meson-nucleon spin-isospin–averaged scattering lengths ${\mathit{a}}_{\mathrm{\rho },\mathrm{\omega },\mathrm{\phi }}$. We found that the crucial matrix elements are 〈q¯${\gamma }_{\mathrm{\mu }}$${\mathit{D}}_{\nu }$q${\mathrm{〉}}_{\mathit{N}}$ (q=ud) (twist-2 nucleon matrix element) for ${\mathit{a}}_{\mathrm{\rho },\mathrm{\omega }}$ and ${\mathit{m}}_{\mathit{s}}$〈s¯s${\mathrm{〉}}_{\mathit{N}}$ for ${\mathit{a}}_{\mathrm{\phi }}$, and obtained ${\mathit{a}}_{\mathrm{\rho }}$=0.14±0.07 fm, ${\mathit{a}}_{\mathrm{\omega }}$=0.11±0.06 fm, and ${\mathit{a}}_{\mathrm{\phi }}$=0.035±0.020 fm. These small numbers originate from a common factor 1/(${\mathit{m}}_{\mathit{N}}$+${\mathit{m}}_{\mathrm{\rho },\mathrm{\omega },\mathrm{\phi }}$). Our result suggests a slight increase (<60 MeV for ρ and ω, and <15 MeV for φ) of the effective mass of these vector mesons in nuclear matter (in the dilute nucleon-gas approximation). The origin of the discrepancy with Hatsuda-Lee was clarified.

We studied parity mixing of the $0_2^{+}$,$0_1^{\mathrm{-}}$; I=1 doublet in ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ (${\mathit{E}}_{\mathit{x}}$∼8.6 MeV) to probe the isoscalar component of the parity nonconserving (PNC) nucleon-nucleon interaction. The weak matrix element connecting the $0^{+}$ and $0^{\mathrm{-}}$ levels was determined by measuring the longitudinal analyzing power (${\mathit{A}}_{\mathit{L}}$) over the narrow ${\mathit{J}}^{\mathrm{\pi }}$=$0^{+13\mathrm{}}$C(p→,p) resonance at ${\mathit{E}}_{\mathit{p}}$=1.16 MeV. Scattered protons were detected in two arrays of four scintillators arranged symmetrically about the beam axis at mean angles of ${\mathit{FTHET}\mathit{Ā}}_1$=35° and ${\mathit{FTHET}\mathit{Ā}}_2$=155°. The PNC signal was the difference in the longitudinal analyzing power observed at the two angles. Feedback loops were used to stabilize the position, angle, and spin direction of the beam on target. The observed signal was ${\mathit{A}}_{\mathit{L}}$(FTHETA${\mathrm{¯}}_2$)-${\mathit{A}}_{\mathit{L}}$(FTHETA${\mathrm{¯}}_1$) =0.9±0.6×${10}^{\mathrm{-}5}$ which corresponds to a weak matrix element 〈${\mathit{H}}_{\mathrm{weak}}$〉=0.38±0.28 eV.

Our measured 〈${\mathit{H}}_{\mathrm{weak}}$〉 disagrees with theoretical expectations; recent shell-model calculations by Horoi et al. using the PNC NN amplitudes of Desplanques, Donoghue, and Holstein yield 〈${\mathit{H}}_{\mathrm{weak}}$〉’s that lie in the range from -0.2 eV to -0.8 eV. We briefly discuss some theoretical uncertainities that arise because the structure of the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ doublet differs in important ways from other known parity doublets. In ancillary studies of the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(p,γ) reaction at ${\mathrm{\theta }}_{\gamma }$=90°, we found that the excitation energies and widths of the $0^{+}$ and $0^{\mathrm{-}}$ levels were (${\mathit{E}}_{\mathit{x}}$=8624±2 keV, Γ=4.0±0.3 keV, and (${\mathit{E}}_{\mathit{x}}$=8802±7 keV, Γ=440±8 keV) respectively. We also determined the following partial widths: ${\mathrm{\Gamma }}_{\gamma }$(8624→0)=(0.37±0.05) eV , ${\mathrm{\Gamma }}_{\gamma }$(8624→3948)=(1.26±0.17) eV, ${\mathrm{\Gamma }}_{\gamma }$(8624→5691)=(0.43±0.06) eV, ${\mathrm{\Gamma }}_{\gamma }$(8624→6204)=(2.03±0.28) eV, and ${\mathrm{\Gamma }}_{\gamma }$(8802→0)=(25.2±2.0) eV. We also report new parameters for the ${\mathit{E}}_{\mathit{x}}$=8062 keV, ${\mathit{E}}_{\mathit{x}}$=9174 keV, and ${\mathit{E}}_{\mathit{x}}$=9388 keV levels.

The two-nucleon parity nonconserving (PNC) interaction induced by the single-particle PNC weak potential and the two-nucleon residual strong interaction is considered. An approximate analytical formula for this induced PNC interaction (IPNCI) between proton and neutron is derived [Q(r${\mathrm{\sigma }}_{\mathit{p}}$×${\mathrm{\sigma }}_{\mathit{n}}$)δ(${\mathbf{r}}_{\mathit{p}}$-${\mathbf{r}}_{\mathit{n}}$)], and the interaction constant is estimated. As a result of coherent contributions from the nucleons to the PNC potential, IPNCI is an order of magnitude stronger (∼${\mathit{A}}^{1/3}$) than the residual weak two-nucleon interaction and has a different coordinate and isotopic structure (e.g., the strongest part of IPNCI does not contribute to the PNC mean field). IPNCI plays an important role in the formation of PNC effects, e.g., in neutron-nucleus reactions. In that case, it is a technical way to take into account the contribution of the distant (small) components of a compound state which dominates the result. The absence of such enhancement (∼${\mathit{A}}^{1/3}$) in the case of T- and P-odd interaction completes the picture.

We make a systematic examination of the role played by the restriction that the cross section in polarized coincidence electronuclear processes must be positive. The necessary formalism for unpolarized scattering structure functions is developed within two frameworks: (i) the response tensor method, and (ii) the Jacob-Wick method. Equivalence of the two methods is demonstrated for unpolarized scattering, and then the simpler Jacob-Wick method is applied to the polarized pseudoscalar electroproduction off a nucleon. We derive three known and eight new inequalities among the polarized target structure functions, as well as 11 new polarized ejectile structure function inequalitites. We also provide rules for this method to be used in the deuteron two-body electrodisintegration in conjunction with the results published in Phys. Rev. C 40, 2479 (1989).

The neutron capture cross sections of ${}_{}{}^{146,148,150}{}_{}{}^{}\mathrm{Nd}$ have been determined relative to that of gold by means of the activation method. The samples were irradiated in a quasistellar neutron spectrum for kT=25 keV using the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,n${)}^7$Be reaction near threshold. Variation of the experimental conditions in different activations and the use of different samples allowed for the reliable determination of corrections and the evaluation of systematic uncertainties. The resulting stellar cross sections can be given with uncertainties around 6%, which represents a considerable improvement compared to previous measurements. These data are complemented by a new set of calculated cross sections for the unstable isotopes ${}_{}{}^{147}{}_{}{}^{}\mathrm{Nd}$, ${}_{}{}^{147,148,149}{}_{}{}^{}\mathrm{Pm}$, and ${}_{}{}^{151}{}_{}{}^{}\mathrm{Sm}$, which act as branching points in the s-process path. Based on these results, the s-process flow in the Nd-Pm-Sm region is discussed with respect to the neutron density during stellar helium burning and to isotopic anomalies in meteorites. The updated s-abundances are also used for a discussion of r- and p-process residuals.

Measurements of the differential cross section for the pion-induced isobaric analog transition in the A=3 system are presented. This measurement, in which low energy recoiling nuclei were detected, is the first at forward pion angles and incident energies where the spin flip (ΔS=1) contribution to the differential cross section is predicted to have its strongest influence. Although the data are not sufficiently accurate to support a definitive conclusion, they agree best with a calculation that includes this contribution.

A high resoution measurement of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{24}$Mg${,}^{12}$${\mathrm{C}}^{12}$C${)}^{12}$C reaction shows that the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ breakup states have widths in the region of 100 to 250 keV. The energies, widths, and spins of these states are seen to be consistent with those of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ${+}^{12}$C quasimolecular resonances which occur in the same region of excitation in the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ nucleus.

The β decay of mass-separated ${}_{}{}^{180}{}_{}{}^{}\mathrm{Yb}$ was investigated by measuring β-delayed γ rays and conversion electrons. Evidence was found for an allowed-unhindered β transition involving the transformation of a 7/$2^{\mathrm{-}}$[514] neutron into a 9/$2^{\mathrm{-}}$[514] proton. The experimental results include a new decay scheme of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Yb}$ which gives evidence for a $5^{+}$ ground state of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Lu}$ and leads to the first identification of further low-spin configurations. These data are compared with predictions obtained from two-quasiparticle band-head energy calculations based on a zero-range residual interaction with appropriate Nilsson model wave functions.

We report on the first measurement of tensor polarization transfer coefficients for the excitation of the 12.7 MeV $1^{+}$ state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ by (d→,d→) inelastic scattering at 393 MeV. The experiment has been performed at Saturne with a tensor polarimeter. The data have allowed the determination of the spin-flip probability ${\mathit{S}}_1$, found to be in good agreement with the approximate signature ${\mathit{S}}_{\mathit{d}}^{\mathit{y}}$ determined previously with a vector polarimeter. The relationships between measured polarizations and analyzing powers are discussed.

Fission cross sections resulting from a 120 MeV/nucleon ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ beam incident upon Be, Al, Cu, Ag, and U targets have recently been measured by Justice et al. [Phys. Rev. C 49, R5 (1994)]. The electromagnetic contribution to these experimental cross sections have been compared to Weizsäcker-Williams theory which is based on first-order perturbation theory. The present work calculates the contribution to these cross sections due to higher-order excitations. Our results show that these corrections are insignificant in comparison to experimental error.

Fusion barriers and fusion cross sections are calculated using the Skyrme energy-density formalism. To study the role of different parametrizations of the Skyrme interaction, we use two typical forces, i.e., the original Skyrme force S and the widely used Skyrme force SIII. Our calculations show that, in the reactions considered here, the Skyrme force S gives higher fusion cross sections compared to that of the Skyrme force SIII. The main part of this difference can be associated with the presence of the spin-density contribution in the Skyrme force SIII.

We propose a method to study refractive scattering by looking at the quantal particle flux within the volume occupied by the nuclear potential. The method is applied to discuss the nuclear halo effects in the elastic scattering of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ at E/A∼60 MeV.

We compute the modified factorization contributions to the Λ→Nρ and Σ→Nρ couplings and demonstrate that these contributions naturally include ΔI=3/2 terms which are comparable (≃0.4 to -0.8 times) in magnitude to the corresponding ΔI=1/2 terms. As a consequence, we conclude models which treat vector meson exchange contributions to the weak conversion process ΛN→NN assuming such weak couplings to satisfy the ΔI=1/2 rule are unlikely to be reliable.

Allowing for 2ħω admixtures in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ we find that the summed magnetic dipole isovector orbital and spin strengths are equal. This indicates a symmetry which is associated with interchanging the labels of the spin with those of the orbit. Where higher admixtures are included, the orbital sum becomes larger than the spin sum, but the sums over the low energy region are still nearly the same.

We demonstrate that the final state p-n interaction in the reaction of electrodissociation of the deuteron at large ${\mathit{Q}}^2$ in a static external field leads to the apparent reacceleration of neutrons. The shift of the neutron velocity from the velocity of the deuteron beam is related to the quantum-mechanical forward-backward asymmetry of the missing momentum distribution in the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ (e,e’p)n scattering.

We study the effect of isospin projections on a two source picture of coherent pions coming from nucleon-antinucleon annihilation. We show that important Hanbury-Brown Twiss correlations among like charge pion pairs compared with unlike arise from these isospin projections.