Showing papers on "Nuclear matter published in 1978"

Pion Fields in Nuclear Matter

Abstract: A comprehensive review is presented dealing with pion excitations and condensation in nucleon matter A discussion of the behavior of bosons in scalar electric and nuclear fields is given along with a consideration of the possible existence of superdense and supercharged nuclei The applications to nuclei and neutron stars are given

Current state of nuclear matter calculations

Abstract: The current state of nuclear matter calculations is described with special reference to the present disagreement between the variational and Brueckner--Bethe methods. The system is assumed to consist of point nucleons with a nonrelativistic Hamiltonian containing the kinetic energy and two-body potentials. The physical ideas of the variational method, especially of its hypernetted-chain version, and of the Brueckner: Bethe method are outlined. Practical ways of testing the validity of these mehtods are discussed and are illustrated by numerical results taken from the literature. It is found for central forces that the hypernetted-chain variational method, if properly used, gives reliable upper bounds to the ground-state energy. Lowest-order Brueckner--Bethe results lie well above these upper bounds, and it is both important and feasible to check whether higher-order corrections will bring the Brueckner--Bethe results into agreement with the variational ones. For realistic nuclear potentials, which have tensor forces, spin--orbit forces, etc., the situation is much less clear. An adequate calculation has not yet been done by either the variational or Brueckner--Bethe method. For the Reid potential, with the presently available numerical results, the variational calculation predicts a much higher saturation density than the Brueckner--Bethe calculation. Feasible calculations that will help to resolve thismore » discrepancy are discussed.« less

Hot Dense Matter and Stellar Collapse

Abstract: We calculate the equation of state for hot dense matter and discuss implications for stellar collapse.

Explosive nucleosynthesis, equilibrium thermodynamics, and relativistic heavy-ion collisions

Abstract: A description of the formation of composite nuclei observed in relativistic heavy-ion collisions is developed. The description is analogous to that used in accounting for the formation of nuclei under explosive conditions, as encountered in the expansion of an isotropic and homogeneous universe and in imploding-exploding supermassive stars. The model studied is one in which composite nuclei are formed in the space-time evolution of a rapidly expanding system of nucleons. Within the framework of this model, it is shown that reaction rates may initially be fast compared to expansion time scales, that detailed balance can then be met, and a quasi-equilibrium established for a short period of time and limited volume of space in this space-time evolution. An idealized equilibrium model is then proposed which contains a sharp cutoff from equilibrium to free expansion. In such a model the observed properties of the composite particles reflect a ''frozen in'' equilibrium state. A simple discussion is then presented showing that the volume at which the transition occurs is related to the finite size of the correlated structures in the system. A key result in the approach developed is that properties of the composite particle cross sections can be used to obtainmore » information on the size of the emitting region without resorting to a Hambury-Brown--Twiss correlation measurement. Another important result is that cross sections for composite nuclei are characterized by Maxwell-Boltzmann distributions is some rest system and recent data will be discussed from this viewpoint. The thermodynamic properties of the system, such as the equation of state and the energy-temperature relationship are investigated. The effect of continuum correlations from resonances and echoes will also be discussed.« less

The collision integral in nuclear matter at zero temperature

Abstract: The collision rate in an infinite Fermi system having a deformed Fermi surface is computed in the limit of small deformation. For a given amount of internal energy, the damping rate is nearly independent of temperature. The calculation is applied to thermalization in heavy ion collisions. We find that the collisional damping time is comparable to the duration of the collision for medium-weight nuclei. Thus the predictions of mean field theory, such as the presence of a fusion window at small impact parameters, will only have validity for lighter ions.

Dependence of particle production in high energy heavy ion collisions on the nuclear equation of state

Abstract: The total pion production cross section in central high energy heavy ion collisions depends strongly on the nuclear equation of state. This fact can be used to detect phase transitions from normal nuclear matter into abnormal superdense states (density isomers).

Neutron star matter at high temperatures and densities. I. Bulk properties of nuclear matter

Abstract: We perform calculations of the thermodynamic properties of uniform dense matter at finite temperature using the Skyrme nuclear interaction. The calculations are valid for arbitrary proton concentrations and temperatures. The equation of state is compared with earlier investigations done for a few restricted cases. In order to understand the conditions under which one might expect to find nuclei immersed in a sea of nucleons, we explore the coexistence of two fluid phases with different proton concentrations. At zero temperature, nuclei with proton fractions in the range 0.044-0.335 may coexist with a pure neutron fluid, but at lower proton fractions protons ''drip'' as well. At finite temperatures, nuclear droplets with proton fractions up to 0.5 may coexist with fluid also containing up to 50% protons. A phase diagram for nuclear matter is presented. The critical temperature, as a function of proton concentration, above which no coexistence is possible and nuclei evaporate, is established. Its maximum value is k/sub B/T=20MeV, which occurs in the cse of symmetric nuclear matter.

Quark stars with ‘realistic’ equations of state

Abstract: THE possibility of a phase transition between nuclear matter and quark matter has been discussed in recent work1–13. Free quarks would presumably appear above a critical density pq, which is greater than the typical density ρn ≃ 2.5 × 1014g cm−3 within ordinary atomic nuclei. Such a transition might allow stable collapsed stars to exist wherein much of the matter is in the form of quark matter (quark stars). The maximum masses of collapsed stars have been investigated for the extreme case of ρq ≃ ρn and hard equations of state for quark matter5. However, it has been argued6,8,9 that some equations of state for quark matter require ρq >> ρn and are therefore unlikely to permit the existence of stable quark stars. We investigate here the properties of collapsed stars in the context of another class of quark-matter models that has recently been proposed11–13. These models12, which are consistent with all experimental nuclear and high-energy physics data, are based on a quantum chromodynamic treatment of quarks that are assumed to be of low mass (≲100 MeV for the lightest quarks). We find that stable quark stars are possible (compare with refs 6, 8, 9). However, we also conclude (compare with refs 5, 14) that such stars need not have significantly different macroscopic properties from those of neutron-star models15–17 based on conventional nuclear-matter equations of state.

Modified one-body nuclear dissipation

Abstract: We study a modification of the one-body dissipation mechanism for the conversion of energy of collective nuclear motion into internal single-particle excitation energy. One-body nuclear dissipation is a consequence of the long mean free path of nucleons inside a nucleus, and arises from nucleons colliding with the moving boundary of the nucleus rather than with other individual nucleons. In our modification, which attempts to incorporate self-consistency, the dissipation rate is proportional to an integral over the nuclear surface of the square of the normal component of the normal derivative of the velocity. The resulting properties of this dissipation are qualitatively similar to those of ordinary two-body viscosity rather than to those of the original one-body dissipation. In particular, for small oscillations about a sphere the dissipation rate increases with increasing multipole degree, and in fission this dissipation leads to more elongated scission shapes and to decreased fission-fragment kinetic energies. By adjusting the parameter that specifies the magnitude of this dissipation, we are able to reproduce adequately the experimental most probable fission-fragment kinetic energies for the fission of nuclei throughout the Periodic Table.

Heavy ion collisions at intermediate energy

Abstract: Two types of measurement are proposed for the analysis of heavy ion collisions in the range of energy of 20-200 MeV/A. First, measurement of the longitudinal component of the kinetic energy of the collision products characterizes the impact parameter of the collision. The distribution in this quantity allows the dissipation in the theoretical models to be determined. A second kind of measurement is that of the coefficients of a spherical harmonic expansion of the angular distribution of the products. Besides giving independent information on the impact parameter and reaction dynamics, measurement of these coefficients offers the possibility of measuring the stiffness of the equation of state of nuclear matter. These ideas are explored in the context of a hydrodynamic model for the collision. In the purely hydrodynamic model there is a large measurable asymmetry in the angular distribution, but the dependence on the equation of state is small.

A constrained variational calculation for beta-stable matter

Abstract: A method of lowest-order constrained variation previously applied by the authors to asymmetric nuclear matter is extended to include electrons and muons making the nucleon fluid electrically neutral and stable against beta decay. The equilibrium composition of a nucleon fluid is calculated as a function of baryon number density and an equation of state for beta-stable matter is deduced for the Reid soft-core interaction.

Constrained variational results for the new Bethe homework problem

Abstract: Bethe (1973) has proposed two model N-N interactions, one containing a central plus sigma 1. sigma 2 spin dependence and the other containing in addition a tensor force to study the convergence of various many-body techniques for calculating the bulk properties of many fermion fluids. Following the success of the authors' constrained variational calculations in describing the behaviour of the original Bethe homework problem involving a purely central interaction, they now present their results in neutron matter and nuclear matter for the new spin-dependent potentials.

Propagation of a deuteron in nuclear matter and the spin dependence of the deuteron optical potential

Abstract: The propagation of a deuteron through nuclear matter is examined in terms of a simple nonlocal but separable potential for the n-p interaction. It is found that the binding energy of the deuteron in nuclear matter depends strongly on the relative orientation of the deuteron spin and center-of-mass momentum, when both the Pauli exclusion principle and the tensor force component in the neutron-proton interaction are included in the calculation. A thorough discussion of the physical mechanism involved is presented. It is shown that this effect is associated with the presence of a new type of spin dependent interaction of the T/sub p/ type, in the deuteron-nucleus optical potential. The nuclear matter calculations are applied to the realistic case of a deuteron scattered by a heavy nucleus through a simple model which is valid for deuteron incident energies in excess of 100 MeV. The T/sub p/ force thus produced is found to have a non-negligible strength over a wide range of high incident deuteron energies and to be very sensitive to high momentum components of the nucleon-nucleon interaction. The mechanism examined here is also expected to generate a T/sub p/ force and a modified T/sub R/ force at low energies. opticalmore » potential. The nuclear matter calculations are applied to the realistic case of a deuteron scattered by a heavy nucleus through a simple model which is valid for deuteron incident energies in excess« less

On pion condensation in finite nuclei

Abstract: The critical pionic state leading to pion condensation is investigated for finite nuclear systems. The threshold density for light nuclei, including4He, is found to be close to that of nuclear matter. For16O and40Ca, the angular momenta of the most critical states areL=0 andL=2.

Theory of hadron plasma

Abstract: The characteristics are calculated of a new state of matter corresponding to densities n and temperatures T such that hcn/sup 1/3/, T> or approx. =1 GeV. This is the hadron plasma in which quarks that are the components of hadrons under ordinary conditions are collectivized. The calculations are performed within the framework of the so-called quantum chromodynamics, i.e., the theory of strong interactions. The results obtain for cold plasma with high density of baryon charge are applied to the collapse of neutron stars and to the problem of the repulsive core of nucleons. Results on the properties of hot neutral plasmas are applied to cosmology and to hadron collisions at high energies.