Showing papers in "Physical Review C in 1988"
TL;DR: The Argonne ${v}_{14}$ plus Urbana VII Hamiltonian produces a softening in the neutron matter equation of state localized around twice nuclear matter density which may indicate a neutral pion condensate.
Abstract: We report microscopic calculations of the equation of state for dense nuclear and neutron matter. The calculations are performed for five Hamiltonians: the Argonne ${v}_{14}$ and Urbana ${v}_{14}$ two-nucleon potentials, both alone and with the Urbana VII three-nucleon potential, and the density-dependent Urbana ${v}_{14}$ plus three-nucleon interaction model of Lagaris, Friedman, and Pandharipande. The beta-stable equation of state and neutron star structure are also calculated for three of the models. The models with the three-nucleon potential bracket the density-dependent model and are significantly stiffer than those with an unmodified two-nucleon potential only. The Argonne ${v}_{14}$ plus Urbana VII Hamiltonian produces a softening in the neutron matter equation of state localized around twice nuclear matter density which may indicate a neutral pion condensate.
767 citations
TL;DR: It is argued that the distinguishable /Lambda/particle provides one of the best examples of single-particle shell structure in nuclear physics.
Abstract: Data on the level spectra of \ensuremath{\Lambda} hypernuclei, obtained from (${\ensuremath{\pi}}^{+}$,${K}^{+}$) and (${K}^{\mathrm{\ensuremath{-}}}$,${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$) reaction studies, are analyzed to obtain a density-dependent and nonlocal \ensuremath{\Lambda}-nucleus potential. We relate our results to previous work which bears on the origin of the density dependence and nonlocality of the \ensuremath{\Lambda}-nucleus potential. We argue that the distinguishable \ensuremath{\Lambda} particle provides one of the best examples of single-particle shell structure in nuclear physics.
252 citations
TL;DR: The systematics of continuum angular distributions in nucleon- and alpha-particle-induced reactions at energies up to several hundred MeV have been studied and parametrized and it has been confirmed that at lower bombarding energies the shapes of the angular distribution are determined mainly by the kinetic energy in the exit channel.
Abstract: The systematics of continuum angular distributions in nucleon- and alpha-particle-induced reactions at energies up to several hundred MeV have been studied and parametrized. It has been confirmed that at lower bombarding energies the shapes of the angular distribution are determined mainly by the kinetic energy in the exit channel, and by the division of the cross section into its multistep direct and multistep compound parts. For incident nucleons with energies above 130 MeV there is a change in the systematics, and the ratio of the energies in the exit and entrance channels of the reaction becomes the important energy parameter. Small second order dependences are also evident for nucleon-induced reactions. The systematics are parametrized using exponentials in cos\ensuremath{\theta} and a small number of universal parameters.
215 citations
TL;DR: Using the quasiparticle random phase approximation, the nuclear matrix elements governing two-neutrino and neutrinoless double-beta decay are calculated and it is shown that a consistent treatment, including both particle-hole and particle-particle interactions, helps to resolve the longstanding discrepancy between experimental and calculated two-NEUTrino decay rates.
Abstract: Using the quasiparticle random phase approximation, we calculate the nuclear matrix elements governing two-neutrino and neutrinoless double-beta decay. We show that a consistent treatment, including both particle-hole and particle-particle interactions, helps to resolve the longstanding discrepancy between experimental and calculated two-neutrino decay rates. The particle-particle force, which allows us to bring calculated EC/β+ decay rates in semimagic nuclei into closer agreement with experiment, is in large part responsible for suppressing calculated two-neutrino decay rates that are otherwise too fast. We test the validity of our procedure by comparing quasiparticle random phase approximation results with exact solutions for a solvable model, in which the suppression of two-neutrino decay by the particle-particle interaction is confirmed. We then extend our approach to the neutrinoless decay associated with a finite Majorana neutrino mass and, conceivably, with majoron emission, and demonstrate that the nuclear matrix elements governing these processes are also suppressed. We present predicted half-lives for both two-neutrino and neutrinoless double-beta decay in several candidate nuclei, and discuss the difficulties associated with the calculation of such highly suppressed quantities.
199 citations
TL;DR: Pion correlations are calculated for a recently proposed model of ultrarelativistic heavy-ion collisions and the model predicts strong correlations between the longitudinal momentum and position of the source.
Abstract: Pion correlations are calculated for a recently proposed model of ultrarelativistic heavy-ion collisions. Ingredients of the model are evaporation of globs of quark-gluon plasma followed by pion scattering in the final state. The model predicts strong correlations between the longitudinal momentum and position of the source. The predicted transverse source size is smaller than preliminary findings from a recent experiment.
190 citations
TL;DR: In this paper, the authors measured the neutron capture cross section of gold using the Be reaction for neutron production and found that the final stellar cross section at kT=25 keV was found to be 648.10 mb.
Abstract: We have measured the neutron capture cross section of gold using the $^{7}\mathrm{Li}$(p,n${)}^{7}$Be reaction for neutron production. This reaction not only provides the integrated neutron flux via the $^{7}\mathrm{Be}$ activity of the target, but also allows for the simulation of a Maxwellian neutron energy spectrum at kT=25 keV. As this spectrum is emitted in a forward cone of 120\ifmmode^\circ\else\textdegree\fi{} opening angle, the cross section can be measured in good geometry and independent of any other standard. Systematic uncertainties were studied experimentally in a series of activations. The final stellar cross section at kT=25 keV was found to be 648\ifmmode\pm\else\textpm\fi{}10 mb, and extrapolation to the common s-process temperature kT=30 keV yields 582\ifmmode\pm\else\textpm\fi{}9 mb. This result is used for renormalization of a number of cross sections which had been measured relative to gold.
170 citations
TL;DR: A detailed microscopic quantum molecular dynamic analysis of fragment formation in the reaction Ne(1.05 GeV/nucleon) + Au, finding that the projectile causes a high density wave to travel through the target and transfers transverse momentum to the intermediate mass fragments.
Abstract: We present a detailed microscopic quantum molecular dynamic analysis of fragment formation in the reaction Ne(1.05 GeV/nucleon) + Au. The theoretical predictions of the total mass yield, the multiplicity distribution of clusters, their average momentum, and their angular distribution agree well with the available data. We find a rather localized hot participant zone, which predominantly emits protons and neutrons. The multiplicity of light clusters depends strongly on the impact parameter whereas the heavier fragments A\ensuremath{\ge}40 result from the decay of spectator residues. Their yield can provide a good measure for the impact parameter. The hypothesis of a compound system of ${A}_{P}$ and ${A}_{T}$ nucleons which is globally heated and equilibrated is not supported by our results. Light and massive fragments occupy different regions in phase space. Semiperipheral reactions do not lead to a stopping of the projectile. We observe a power law behavior of the inclusive mass yield distribution. Its form, however, is caused by averaging over different impact parameters. This rules out inclusive mass yield distributions as candidates for revealing a possible liquid gas phase transition. Light and intermediate mass fragments are formed during the early compressional stage of the reaction. We find that the projectile causes a high density wave to travel through the target. It causes the target to fragment and transfers transverse momentum to the intermediate mass fragments. Lighter fragments receive additional momentum transfer due to n-n collisions.
150 citations
TL;DR: In this article, relativistic calculations of elastic electromagnetic form factors of the deuteron are presented for momentum transfers up to 8 GeV/sup 2/ Standard nucleon-nucleon interactions are used to construct a unitary representation of the inhomogeneous Lorentz group on the two-nule Hilbert space Deuteron wave functions represent eigenstates of the four-momentum operator.
Abstract: Relativistic calculations of elastic electromagnetic form factors of the deuteron are presented for momentum transfers up to 8 GeV/sup 2/ Standard nucleon-nucleon interactions are used to construct a unitary representation of the inhomogeneous Lorentz group on the two-nucleon Hilbert space Deuteron wave functions represent eigenstates of the four-momentum operator Existing parametrizations of measured single-nucleon form factors are used to construct a conserved covariant electromagnetic current operator Deuteron form factors are computed in terms of matrix elements of the current operator and the deuteron wave functions The results are compared to experiment The size of relativistic effects, scaling behavior, sensitivity to the nucleon-nucleon interactions, and effects of the uncertainties in measured nucleon form factors are investigated
116 citations
TL;DR: Variations of the parametrization and of the data which suggest that the present fit has exhausted the limits of the mean-field approximation are discussed, and extensions which go beyond the mean field are discussed.
Abstract: We study a relativistic model of the nucleus consisting of nucleons coupled to mesonic degrees of freedom via an effective Lagrangian whose parameters are determined by a fit to selected nuclear ground-state data. We find that the model allows a very good description of nuclear ground-state properties. Because of the relativistic nature of the model, the spin properties are uniquely fixed. We discuss variations of the parametrization and of the data which suggest that the present fit has exhausted the limits of the mean-field approximation, and discuss extensions which go beyond the mean field.
107 citations
TL;DR: A model is proposed that takes full advantage of both the shell and cluster models in order to describe a system of valence nucleons weakly coupled to a core, and is applied to the neutron-rich He isotopes with reasonable success.
Abstract: A model is proposed in which we take full advantage of both the shell and cluster models in order to describe a system of valence nucleons weakly coupled to a core. This is realized by introducing radius vectors of the valence nucleons relative to the core, new coordinates of independent particle nature. The model is applied to the neutron-rich He isotopes, $^{6\mathrm{\ensuremath{-}}8}\mathrm{He}$, with reasonable success.
97 citations
TL;DR: For near central collisions of Nb on Nb at a laboratory energy of 650 MeV per projectile nucleon, inclusive cross sections are calculated as a function of the azimuthal angle where this angle is measured from the reaction plane.
Abstract: For near central collisions of Nb on Nb at a laboratory energy of 650 MeV per projectile nucleon we calculate inclusive cross sections as a function of the azimuthal angle where this angle is measured from the reaction plane. The azimuthal dependence is strongly influenced by the nuclear equation of state and is a useful quantity to measure.
TL;DR: From studying the transverse momentum distribution in heavy-ion collisions, it is concluded that the nuclear equation of state at high density is softer than that determined previously using the normal Vlasov-Uehling-Uhlenbeck model and is consistent with that from the analysis with a momentum-dependent potential.
Abstract: The previously derived relativistic Vlasov equation from the Walecka model is generalized to include both a collision term and the self-interaction of the scalar meson. From studying the transverse momentum distribution in heavy-ion collisions, we conclude that the nuclear equation of state at high density is softer than that determined previously using the normal Vlasov-Uehling-Uhlenbeck model and is consistent with that from the analysis with a momentum-dependent potential. We have also found that in relativistic model the magnitude of the transverse momentum from heavy-ion collision is more sensitive to the value of the nucleon effective mass at saturation density than the value of the compressibility at this density.
TL;DR: The low-energy spectroscopy of odd-A nuclei in the mass region Aapprox.219--229 is modeled by coupling states of a deformed shell model including octupole deformation to a reflection-asymmetric rotor core including oct upole deformed to a reflected rotor core to evaluate the model.
Abstract: The low-energy spectroscopy of odd-A nuclei in the mass region A\ensuremath{\sim}219--229 is modeled by coupling states of a deformed shell model including octupole deformation to a reflection-asymmetric rotor core. Theory and experiment are compared for the nuclei in which data are available: $^{219}$,221,223,225Rn, $^{221}$,223,225,227Fr, $^{219,221,223,225,227}\mathrm{Ra}$, $^{219,223,225,227,229}\mathrm{Ac}$ $^{221,223,225,227,229}\mathrm{Th}$, and $^{229}\mathrm{Pa}$. Overall agreement requires an octupole deformation ${\ensuremath{\beta}}_{3}$\ensuremath{\sim}0.1. The results throughout the region are synthesized to evaluate the model.
TL;DR: Within the context of the relativistic Fermi gas model, the concept of ''y scaling'' for inclusive electron scattering from nuclei is investigated and specific kinematic shifts of the single-nucleon response in the nuclear medium can be incorporated with this model.
Abstract: Within the context of the relativistic Fermi gas model, the concept of ``y scaling'' for inclusive electron scattering from nuclei is investigated. Specific kinematic shifts of the single-nucleon response in the nuclear medium can be incorporated with this model. Suggested generalizations beyond the strict Fermi gas model, including treatments of separated longitudinal and transverse responses, are also explored.
TL;DR: A multienergy phase shift analysis of all published proton-proton scattering data in the energy range ${T}_{\mathrm{lab}\mathrm{\ensuremath{\le}}30}$ MeV is presented, including the well-known long-range interaction: the improved Coulomb, the vacuum polarization, and the one-pion-exchange potential.
Abstract: A multienergy phase shift analysis of all published proton-proton (pp) scattering data in the energy range ${T}_{\mathrm{lab}\mathrm{\ensuremath{\le}}30}$ MeV is presented. In the description of all partial waves the well-known long-range interaction is included: the improved Coulomb, the vacuum polarization, and the one-pion-exchange potential. In the lower partial waves the energy-dependent analysis uses a P-matrix parametrization for the short-range interaction. Special attention is paid to the electric interaction, the definition of the phase shifts, and the selection of the data. The fit to the final data set comprising 360 scattering observables results in ${\ensuremath{\chi}}^{2}$/${N}_{\mathrm{df}=1.0}$, where ${N}_{\mathrm{df}}$ is the number of degrees of freedom. The pp${\ensuremath{\pi}}^{0}$ coupling constant is determined to be ${\mathit{g}}_{\mathrm{pp}}$${\mathrm{\ensuremath{\pi}}}_{^{2}}^{0}$/4\ensuremath{\pi}=14.5\ifmmode\pm\else\textpm\fi{}1.2, but there are several indications for a lower value. The optimum value for the P-matrix radius b\ensuremath{\approxeq}1.4 fm is satisfying. Single-energy phase shifts with second derivative matrices, and effective range parameters are given.
TL;DR: A study of the systematics of the breathing mode giant monopole resonance in the isotopic chains of Sn and Sm nuclei by means of inelastic scattering of 120 MeV alpha particles at 0\ifmmode^\circ\else\textdegree\fi{} has been performed.
Abstract: A study of the systematics of the breathing mode giant monopole resonance in the isotopic chains of Sn and Sm nuclei by means of inelastic scattering of 120 MeV alpha particles at 0\ifmmode^\circ\else\textdegree\fi{} has been performed. The obtained energy systematics for spherical Sn and Sm nuclei have been employed to fit the nuclear-compressibility parameters. The data on Sn and Sm nuclei have been used in conjunction with already existing data on $^{208}\mathrm{Pb}$ and $^{24}\mathrm{Mg}$ to constrain the various parameters contributing to the nuclear compressibility. The compressibility of nuclear matter ${K}_{\ensuremath{\infty}}$ has been deduced to be 300\ifmmode\pm\else\textpm\fi{}25 MeV, in contrast with the commonly accepted value of 210\ifmmode\pm\else\textpm\fi{}30 MeV. The neutron-asymmetry term has been determined to be -320\ifmmode\pm\else\textpm\fi{}180 MeV.
TL;DR: It is shown that the percolation model of nuclear fragmentation is able to reproduce experimental results for inclusive mass yields, while only using very simple physical assumptions, and how to extract possible signals of a phase transition and information on its specific nature.
Abstract: We use a percolation model of nuclear fragmentation to study the possibility of observing a phase transition of nuclear matter in collisions of high-energy (> 10 GeV) protons with heavy targets. It is shown that the model is able to reproduce experimental results for inclusive mass yields, while only using very simple physical assumptions. By employing event by event analysis of the moments of the mass distributions it is shown how to extract possible signals of a phase transition and information on its specific nature. Special attention is focused on the influence of the size of the fragmenting system on our ability to observe the phase transition.
TL;DR: From measurements of the spallation cross sections of carbon, oxygen, and iron in helium and hydrogen, at beam energies from 540 to 1600 MeV/nucleon, an empirical formula is derived that is found in good agreement with available isotopic cross sections data from radioactivity and radiochemical techniques.
Abstract: We present measurements of the spallation cross sections of carbon, oxygen, and iron in helium and hydrogen, at beam energies from 540 to 1600 MeV/nucleon, performed by exposing liquid helium, CH2, and C targets. Charge changing cross sections are reported for fragments down to Ne for Fe + alpha and Fe + p reactions, and down to B for O + alpha, O + p, C + alpha, and C + p reactions. Alpha- to p-induced cross section ratios (sigma(sub alpha)/sigma(sub p)) are determined at the same energy per nucleon. From these measurements an empirical formula for the (sigma(sub alpha)/sigma(sub p)) ratios is derived and is found in good agreement with available isotopic cross sections data from radioactivity and radiochemical techniques. These results are applied to the propagation of heavy charged cosmic rays in an interstellar medium with a helium to hydrogen abundance ratio of 0.10. It is shown that the Sc-Mn/Fe ratio prediction is decreased relative to the B/C ratio when compared to propagation calculations in a pure hydrogen interstellar medium.
TL;DR: ''Best-fit'' parameters in terms of the phenomenological optical model were extracted from the data including in addition differential cross section and analyzing power data from the literature.
Abstract: Differential cross sections of elastic scattering of deuterons on the target nuclei $^{27}\mathrm{Al}$, $^{89}\mathrm{Y}$, $^{120}\mathrm{Sn}$, and $^{208}\mathrm{Pb}$ were measured at ${E}_{d}$=58.7 MeV and ${E}_{d}$=85 MeV. ``Best-fit'' parameters in terms of the phenomenological optical model were extracted from the data including in addition differential cross section and analyzing power data from the literature. A set of global optical potential parameters is derived.
TL;DR: A complete derivation of a new two-variable integrodifferential equation valid for three- and many-boson systems is given here for the first time, and it is shown to be exact if all correlations higher than those of two-body type can be neglected.
Abstract: A complete derivation of a new two-variable integrodifferential equation valid for three- and many-boson systems is given here for the first time, and it is shown to be exact if all correlations higher than those of two-body type can be neglected. Its equivalence to the Faddeev equation for three bodies and its applicability to many-body systems are discussed in detail. Three-body forces are included. It is shown that the three- and four-body binding energies obtained by means of this equation are in good agreement with those obtained from the most sophisticated variational, Faddeev, and Faddeev-Yakubovsky calculations. This indicates that our new two-variable integrodifferential equation should also be useful for larger systems, in particular since unlike other methods it does not suffer from the disadvantage of rapidly increasing complexity with A. We also show that a simple adiabatic method for the solution of this equation (and hence also for the Faddeev equation) is quite sufficient, due to the closeness of the upper and lower bounds obtained in this way. Finally we apply the adiabatic method to nuclear three-body scattering and even include the effect of breakup for spin-dependent forces. It is found that asymptotic behavior is reached for a value ofmore » the hyperradius of the order of 35 fm.« less
TL;DR: Variational calculations are presented for the Argonne, Bonn r space, Reid V8, and Nijmegen nucleon-nucleon interaction models, as well as results obtained with the Urbana model 7 three-n DNA interaction.
Abstract: The structure of the alpha particle is examined through microscopic studies with a variety of interaction models. Variational calculations are presented for the Argonne, Bonn r space, Reid V8, and Nijmegen nucleon-nucleon interaction models, as well as results obtained with the Urbana model 7 three-nucleon interaction. Green's function Monte Carlo results are reported for the Reid V8 interaction and compared with variational results to illustrate the strengths and shortcomings of the variational method. In addition to ground-state energies, one- and two-body distribution functions are shown for the various models, as well as D-state probabilities. Information about the distribution can, in principle, be determined from electron scattering, while the D-state probability may be accessible through d+d..--> cap alpha..+..gamma.. experiments.
TL;DR: In this paper, the isomeric cross-section ratio for the formation of /sup 73/sup m/sup,//sup g/Se was determined in the /sup 70/Ge(..cap alpha..,n) reaction over the energy range of 13--27 MeV, in the/sup nat/Ge (/sup 3/He,xn) process over 13--24 MeV.
Abstract: The isomeric cross-section ratio sigma/sub m//(sigma/sub m/+sigma/sub g/) for the formation of /sup 73//sup m//sup ,//sup g/Se was determined in the /sup 70/Ge(..cap alpha..,n) reaction over the energy range of 13--27 MeV, in the /sup nat/Ge(/sup 3/He,xn) process over 13--24 MeV, in the /sup 75/As(p,3n) reaction over 25--45 MeV, and in the /sup 75/As(d,4n) reaction over 28--56 MeV. Measurements were done radiochemically using the ''stacked-foil'' technique. In (..cap alpha..,n) and (/sup 3/He,xn) processes the ratio is relatively high at low incident particle energies but decreases with increasing energy. In (p,3n) and (d,4n) reactions, on the other hand, it is practically constant. Statistical model calculations taking into account precompound emission were carried out on the four processes investigated in this work as well as on the /sup 74/Se(n,2n) reaction reported in the literature. The total cross section (sigma/sub m/+sigma/sub g/) is described well by the calculation. The calculated isomeric cross-section ratio depends strongly on the input level scheme of the product nucleus. In general, however, the statistical model, under a suitable set of global assumptions, can reproduce the isomeric cross-section ratio in all the five nuclear processes.
TL;DR: For deformed nuclei and the actinides, the B(E2)up-arrow values calculated in a schematic single-particle ''SU(3)'' simulation or large single-j simulation of major shells successfully reproduce not only the empirical variation of these values but also the observed saturation ofThese values when plotted againstmore » N/sub p/N/sub n/.
Abstract: We have completed a compilation of experimental results for the electric quadrupole transition probability B(E2)\ensuremath{\uparrow} between the ${0}^{+}$ ground state and the first ${2}^{+}$ state in even-even nuclei. The adopted B(E2)\ensuremath{\uparrow} values have been employed to test the various systematic, empirical, and theoretical relationships proposed by several authors (Grodzins, Bohr and Mottelson, Wang et al., Ross and Bhaduri, Patnaik et al., Hamamoto, Casten, M\"oller and Nix, and Kumar) on a global, local, or regional basis. These systematics offer methods for making reasonable predictions of unmeasured B(E2) values. For nuclei away from closed shells, the SU(3) limit of the intermediate boson approximation implies that the B(E2)\ensuremath{\uparrow} values are proportional to (${e}_{\mathrm{p}{N}_{\mathrm{p}+{e}_{\mathrm{n}{N}_{\mathrm{n}{)}^{2}}}}}$, where ${e}_{\mathrm{p}({e}_{\mathrm{n}}}$) is the proton (neutron) effective charge and ${N}_{\mathrm{p}}$ (${N}_{\mathrm{n}}$) refers to the number of valence protons (neutrons). This proportionality is consistent with the observed behavior of B(E2)\ensuremath{\uparrow} vs ${N}_{\mathrm{p}{N}_{\mathrm{n}}}$. For deformed nuclei and the actinides, the B(E2)\ensuremath{\uparrow} values calculated in a schematic single-particle ``SU(3)'' simulation or large single-j simulation of major shells successfully reproduce not only the empirical variation of the B(E2)\ensuremath{\uparrow} values but also the observed saturation of these values when plotted against ${N}_{\mathrm{p}{N}_{\mathrm{n}}}$. .AE
TL;DR: A model Hamiltonian is advanced which provides a computationally efficient means of investigating nuclear dynamics and it is shown that the binding energies per nucleon and rms radii of these ground states are close to the measured values over a wide mass range.
Abstract: A model Hamiltonian is advanced which provides a computationally efficient means of investigating nuclear dynamics. The Hamiltonian includes both Coulomb and isospin-dependent terms, and incorporates antisymmetrization effects through a momentum-dependent potential. Unlike many other classical or semiclassical models, the nuclei of this simulation have a well-defined ground state with a nonvanishing . It is shown that the binding energies per nucleon and rms radii of these ground states are close to the measured values over a wide mass range.
TL;DR: Flow effects parametrized further using the sphericity tensor are found stronger than in the cascade model and consistently weaker than predicted by hydrodynamics.
Abstract: Semicentral Ar+KCl, La+La, and Ar+Pb collisions at 800 MeV/nucleon were studied using a streamer chamber. The results are analyzed in the framework of the transverse momentum analysis and in terms of the average sphericity matrix. A critical examination of the analysis procedures, both experimental and theoretical, is given. New procedures are described to account for overall momentum conservation in the reaction, and to correct for azimuthal variations in the detection efficiency. Average transverse momenta per nucleon in the reaction plane are presented for deuterons emitted in the forward hemisphere, as these provide the most reliable information. A Vlasov-Uehling-Uhlenbeck calculation with a stiff equation of state gives a good fit to the momenta in the Ar+Pb reaction. Flow effects parametrized further using the sphericity tensor are found stronger than in the cascade model and consistently weaker than predicted by hydrodynamics. Parameters from the sphericity tensor exhibit a larger variation as a function of multiplicity than do the average momenta per nucleon.
TL;DR: It is concluded that supernova explosions have not been proven to provide a significant constraint on the nuclear equation of state and the theoretical bias used to interpret data on neutron star masses as if they belonged to a population all having the same mass is unjustified.
Abstract: Data on the nuclear equation of state from a number of different sources, from nuclei, high energy nuclear collisions, supernova, and neutron stars are analyzed. The current situation concerning supernova simulations is critically appraised. It is found that simulations that have achieved a prompt ejection do so with an equation of state that is too soft to support the measured masses of several known neutron stars. It is concluded that supernova explosions have not been proven to provide a significant constraint on the nuclear equation of state. Additionally it is concluded that the theoretical bias used to interpret data on neutron star masses as if they belonged to a population all having the same mass (of 1.4M/sub sun/) is unjustified. Evidence from the various nuclear data and neutron star masses favor a high compression modulus, Kapprox. =300 MeV. No definitive statement can be made about the equation of state at higher density, save that the neutron star equation of state must be moderately stiff to accommodate neutron stars of mass approx. =1.85M/sub sun/.
TL;DR: In this article, a semiclassical model for the calculation of energy spectra of one nucleon transfer reactions to continuum states is presented and both isolated and overlapping resonances can be discussed.
Abstract: A semiclassical model is presented for the calculation of energy spectra of one nucleon transfer reactions to continuum states. Both isolated and overlapping resonances can be discussed. The theory is applied to medium energy heavy-ion reactions and the calculated spectra show general trends in agreement with the experimental data.
TL;DR: The calculated results are in good agreement with the recent experiments which further demonstrates that the average ..lambda.. nucleus well can be simulated by an appropriate Woods-Saxon type potential over a wide mass range of hypernuclei to a good approximation.
Abstract: The (${\ensuremath{\pi}}^{+}$,${K}^{+}$) strength functions (cross sections) are systematically calculated in the distorted-wave impulse approximation for the production of light-to-heavy hypernuclei: $_{\mathrm{\ensuremath{\Lambda}}}^{12}\mathrm{C}$, $_{\mathrm{\ensuremath{\Lambda}}}^{16}\mathrm{O}$, $_{\mathrm{\ensuremath{\Lambda}}}^{28}\mathrm{Si}$, $_{\mathrm{\ensuremath{\Lambda}}}^{40}\mathrm{Ca}$, $_{\mathrm{\ensuremath{\Lambda}}}^{56}\mathrm{Fe}$, $_{\mathrm{\ensuremath{\Lambda}}}^{90}\mathrm{Zr}$ (and $_{\mathrm{\ensuremath{\Lambda}}}^{208}\mathrm{Pb}$). The quasifree continuum effects are taken into account in the frameworks of the Kapur-Peierls method and also of the continuum shell model. The characteristic feature of the (${\ensuremath{\pi}}^{+}$,${K}^{+}$) reaction is to provide well-separated series of peaks with high spin corresponding to the bound and resonant \ensuremath{\Lambda} states, yielding information on deep-lying hyperon states in heavy nuclei as well. Reasons for this effectiveness are clarified and discussed. The calculated results are in good agreement with the recent experiments which further demonstrates that the average \ensuremath{\Lambda} nucleus well can be simulated by an appropriate Woods-Saxon type potential (${V}_{0}$\ensuremath{\approxeq}-30 MeV) over a wide mass range of hypernuclei to a good approximation.
TL;DR: A first application to high-energy photon production is presented and the influence of the equation of state on the differential photon yield is studied and it is found that residual two-particle collisions might even slightly reduce the transverse momentum p/sub t/ due to an increase of stopping power obtained from the collisions.
Abstract: We present a covariant transport theory for heavy-ion collisions based on the sigma-..omega.. model. The two-body collision term is introduced in line with relativistic classical kinetic theory assuming the free nucleon-nucleon cross section in the collision integral. Within this approach, we study collisions of /sup 16/O+/sup 16/O at 600 MeV/nucleon for two different parameter sets of the underlying Lagrangian density, i.e., different equations of state. The most striking result is the strong sensitivity of the transverse momentum distribution on the momentum dependence of the mean field which is self-consistently included in the relativistic approach. We find that residual two-particle collisions might even slightly reduce the transverse momentum p/sub t/ due to an increase of stopping power obtained from the collisions. An increase of the cross section by a factor of 2 leads to a much smaller enhancement of p/sub t/ than observed in nonrelativistic calculations with a momentum independent mean field. We furthermore present a first application to high-energy photon production and study the influence of the equation of state on the differential photon yield.
TL;DR: The astrophysical reaction rate, N/sub A/ , was calculated from the measured cross sections for the combined p/sub 0/ and p/ sub 1/ transitions, and the resulting reaction rate is approximately 60--80 % of the rate currently in use.
Abstract: The total $^{7}\mathrm{Be}$(n,p${)}^{7}$Li cross section has been measured from 25 meV to 13.5 keV. These energies correspond to temperatures of T=2.9\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ to 0.16 GK. For thermal neutrons the cross sections to the ground state (${p}_{0}$) and the first excited state (${\mathit{p}}_{1}$) of $^{7}\mathrm{BLi}$ are 38 400\ifmmode\pm\else\textpm\fi{}800 b and 420\ifmmode\pm\else\textpm\fi{}120 b, respectively. This result for the total $^{7}\mathrm{Be}$(n,p${)}^{7}$Li thermal cross section is about 25% lower, and is approximately a factor of 10 more precise than previous published measurements. For energies above 100 eV, a significant departure from a 1/v shape for the total cross section is observed. The data were analyzed using a single-level approximation, and were also analyzed together with other data using multilevel-multichannel R-matrix theory. Results are presented for the properties of the ${2}^{\mathrm{\ensuremath{-}}}$ threshold state and for a possible nearby ${2}^{\mathrm{\ensuremath{-}}}$ state. The astrophysical reaction rate, ${N}_{A}$〈\ensuremath{\sigma}v〉, was calculated from the measured cross sections for the combined ${p}_{0}$ and ${p}_{1}$ transitions. The resulting reaction rate is approximately 60--80 % of the rate currently in use. This reduction in the $^{7}\mathrm{Be}$(n,p${)}^{7}$Li reaction rate could result in a calculated increase in the production of $^{7}\mathrm{Li}$ during the big bang by as much as 20%.