arXiv subjects

S. Shlomo

Publications and source records attributed to S. Shlomo.

46 records · Page 3Linked to original sources

arXiv2001

Equation of state and phase transitions in asymmetric nuclear matter

The structure of the 3-dimension pressure-temperature-asymmetry surface of equilibrium of the asymmetric nuclear matter is studied within the thermal Thomas-Fermi approximation. Special attention is paid to the difference of the asymmetry parameter between the boiling sheet and that of the condensation sheet of the surface of equilibrium. We derive the condition of existence of the regime of retrograde condensation at the boiling of the asymmetric nuclear matter. We have performed calculations of the caloric curves in the case of isobaric heating. We have shown the presence of the plateau region in caloric curves at the isobaric heating of the asymmetric nuclear matter. The shape of the caloric curve depends on the pressure and is sensitive to the value of the asymmetry parameter. We point out that the experimental value of the plateau temperature T \approx 7 MeV corresponds to the pressure P = 0.01 MeV/fm^3 at the isobaric boiling.

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arXiv2001

Sound modes in hot nuclear matter

The propagation of the isoscalar and isovector sound modes in a hot nuclear matter is considered. The approach is based on the collisional kinetic theory and takes into account the temperature and memory effects. It is shown that the sound velocity and the attenuation coefficient are significantly influenced by the Fermi surface distortion (FSD). The corresponding influence is much stronger for the isoscalar mode than for the isovector one. The memory effects cause a non-monotonous behavior of the attenuation coefficient as a function of the relaxation time leading to a zero-to-first sound transition with increasing temperature. The mixing of both the isoscalar and the isovector sound modes in an asymmetric nuclear matter is evaluated. The condition for the bulk instability and the instability growth rate in the presence of the memory effects is studied. It is shown that both the FSD and the relaxation processes lead to a shift of the maximum of the instability growth rate to the longer wave length region.

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arXiv2001

Memory effects on descent from nuclear fission barrier

Non-Markovian transport equations for nuclear large amplitude motion are derived from the collisional kinetic equation. The memory effects are caused by the Fermi surface distortions and depend on the relaxation time. It is shown that the nuclear collective motion and the nuclear fission are influenced strongly by the memory effects at the relaxation time $τ\geq 5\cdot 10^{-23}{\rm s}$. In particular, the descent of the nucleus from the fission barrier is accompanied by characteristic shape oscillations. The eigenfrequency and the damping of the shape oscillations depend on the contribution of the memory integral in the equations of motion. The shape oscillations disappear at the short relaxation time regime at $τ\to 0$, which corresponds to the usual Markovian motion in the presence of friction forces. We show that the elastic forces produced by the memory integral lead to a significant delay for the descent of the nucleus from the barrier. Numerical calculations for the nucleus $^{236}$U shows that due to the memory effect the saddle-to-scission time grows by a factor of about 3 with respect to the corresponding saddle-to-scission time obtained in liquid drop model calculations with friction forces.

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arXiv2000

Isoscalar Giant Dipole Resonance and Nuclear Matter Incompressibility Coefficient

We present results of microscopic calculations of the strength function, S(E), and alpha-particle excitation cross sections sigma(E) for the isoscalar giant dipole resonance (ISGDR). An accurate and a general method to eliminate the contributions of spurious state mixing is presented and used in the calculations. Our results provide a resolution to the long standing problem that the nuclear matter incompressibility coefficient, K, deduced from sigma(E) data for the ISGDR is significantly smaller than that deduced from data for the isoscalar giant monopole resonance (ISGMR).

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arXiv1999

Collisional relaxation of collective motion in a finite Fermi liquid

Finite size effects in the equilibrium phase space density distribution function are taken into account for alculations of the relaxation of collective motion in finite nuclei. Memory effects in the collision integral and the diffusivity and the quantum oscillations of the equilibrium distribution function in momentum space are considered. It is shown that a smooth diffuse (Fermi-type) equilibrium distribution function leads to a spurious contribution to the relaxation time. The residual quantum oscillations of the equilibrium distribution function eliminates the spurious contribution. It ensures the disappearance of the gain and loss terms in the collision integral in the ground state of the system and strongly reduces the internal collisional width of the isoscalar giant quadrupole resonances.

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arXiv1998

Low density instability in a nuclear Fermi liquid drop

The instability of a Fermi-liquid drop with respect to bulk density distortions is considered. It is shown that the presence of the surface strongly reduces the growth rate of the bulk instability of the finite Fermi-liquid drop because of the anomalous dispersion term in the dispersion relation. The instability growth rate is reduced due to the Fermi surface distortions and the relaxation processes. The dependence of the bulk instability on the multipolarity of the particle density fluctuations is demonstrated for two nuclei $^{40}Ca$ and $^{208}Pb$.

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arXiv1997

Effect of Flow on Caloric Curve for Finite Nuclei

In a finite temperature Thomas-Fermi theory, we construct caloric curves for finite nuclei enclosed in a freeze-out volume few times the normal nuclear volume, with and without inclusion of flow. Without flow, the caloric curve indicates a smooth liquid-gas phase transition whereas with flow, the transition may be very sharp. We discuss these results in the context of two recent experiments, one for heavy symmetric system (Au + Au at 600A MeV) and the other for highly asymmetric system (Au + C at 1A GeV) where different behaviours in the caloric curves are seen.

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arXiv1997

Liquid-gas phase transition in finite nuclei

In a finite temperature Thomas-Fermi framework, we calculate density distributions of hot nuclei enclosed in a freeze-out volume of few times the normal nuclear volume and then construct the caloric curve, with and without inclusion of radial collective flow. In both cases, the calculated specific heats $C_v$ show a peaked structure signalling a liquid-gas phase transition. Without flow, the caloric curve indicates a continuous phase transition whereas with inclusion of flow, the transition is very sharp. In the latter case, the nucleus undergoes a shape change to a bubble from a diffuse sphere at the transition temperature.

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arXiv1997

Caloric Curve for Finite Nuclei in Thomas-Fermi Theory

In a finite temperature Thomas-Fermi theory with realistic nuclear interactions, we construct caloric curves for finite nuclei enclosed in a sphere of about $4 - 8$ times the normal nuclear volume. The specific heat capacity $C_v$ shows a peaked structure that is possibly indicative of a liquid-gas phase transition in finite nuclear systems.

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arXiv1996

Nuclear Shape Fluctuations in Fermi-Liquid Drop Model

Within the nuclear Fermi-liquid drop model, quantum and thermal fluctuations are considered by use of the Landau-Vlasov-Langevin equation. The spectral correlation function of the nuclear surface fluctuations is evaluated in a simple model of an incompressible and irrotational Fermi liquid. The dependence of the spectral correlation function on the dynamical Fermi-surface distortion is established. The temperature at which the eigenvibrations become overdamped is calculated. It is shown that, for realistic values of the relaxation time parameter and in the high temperature regime, there is a particular eigenmode of the Fermi liquid drop where the restoring force is exclusively due to the dynamical Fermi-surface distortion.

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