73,872 research outputs found
Statistical description of complex nuclear phases in supernovae and proto-neutron stars
We develop a phenomenological statistical model for dilute star matter at
finite temperature, in which free nucleons are treated within a mean-field
approximation and nuclei are considered to form a loosely interacting cluster
gas. Its domain of applicability, that is baryonic densities ranging from about
g cm to normal nuclear density, temperatures between
1 and 20 MeV and proton fractions between 0.5 and 0, make it suitable for the
description of baryonic matter produced in supernovae explosions and
proto-neutron stars. The first finding is that, contrary to the common belief,
the crust-core transition is not first order, and for all subsaturation
densities matter can be viewed as a continuous fluid mixture between free
nucleons and massive nuclei. As a consequence, the equations of state and the
associated observables do not present any discontinuity over the whole
thermodynamic range. We further investigate the nuclear matter composition over
a wide range of densities and temperatures. At high density and temperature our
model accounts for a much larger mass fraction bound in medium nuclei with
respect to traditional approaches as Lattimer-Swesty, with sizeable
consequences on the thermodynamic quantities. The equations of state agree well
with the presently used EOS only at low temperatures and in the homogeneous
matter phase, while important differences are present in the crust-core
transition region. The correlation among the composition of baryonic matter and
neutrino opacity is finally discussed, and we show that the two problems can be
effectively decoupled.Comment: 40 pages, 25 figure
Multifragmentation and the symmetry term of the nuclear equation of state
We investigate the possibility to extract the symmetry energy from
multifragmentation data. The applicability of the grandcanonical formula
earlier proposed by Ono {\it et al.} [Phys. Rev. C {\bf 68}, 051601(R)] in the
case of finite excited nuclei is tested within a microcanonical framework.
Relatively good results are obtained except for large residual nuclei,
especially when large sources are highly excited. Effects of secondary particle
emission and the extent in which relevant information may be inferred from
experimental observables are finally discussed.Comment: 13 pages, 4 figure
Unified treatment of sub-saturation stellar matter at zero and finite temperature
The standard variational derivation of stellar matter structure in the
Wigner-Seitz approximation is generalized to the finite temperature situation
where a wide distribution of different nuclear species can coexist in the same
density and proton fraction condition, possibly out of -equilibrium. The
same theoretical formalism is shown to describe on one side the single-nucleus
approximation (SNA), currently used in most core collapse supernova
simulations, and on the other side the nuclear statistical equilibrium (NSE)
approach, routinely employed in r- and p-process explosive nucleosynthesis
problems. In particular we show that in-medium effects have to be accounted for
in NSE to have a theoretical consistency between the zero and finite
temperature modeling. The bulk part of these in-medium effects is analytically
calculated and shown to be different from a van der Waals excluded volume term.
This unified formalism allows controlling quantitatively the deviations from
the SNA in the different thermodynamic conditions, as well as having a NSE
model which is reliable at any arbitrarily low value of the temperature, with
potential applications for neutron star cooling and accretion problems. We
present different illustrative results with several mass models and effective
interactions, showing the importance of accounting for the nuclear species
distribution even at temperatures lower than 1 MeV.Comment: 26 pages, 17 figures; submitted to Phys. Rev.
Exotic Hadrons with Hidden Charm and Strangeness
We investigate on exotic tetraquark hadrons of the kind [cs][cbar sbar] by
computing their spectrum and decay modes within a constituent
diquark-antidiquark model. We also compare these predictions with the present
experimental knowledge.Comment: 6 pages, 2 figures, minor changes made, references adde
Echos of the liquid-gas phase transition in multifragmentation
A general discussion is made concerning the ways in which one can get
signatures about a possible liquid-gas phase transition in nuclear matter.
Microcanonical temperature, heat capacity and second order derivative of the
entropy versus energy formulas have been deduced in a general case. These
formulas are {\em exact}, simply applicable and do not depend on any model
assumption. Therefore, they are suitable to be applied on experimental data.
The formulas are tested in various situations. It is evidenced that when the
freeze-out constraint is of fluctuating volume type the deduced (heat capacity
and second order derivative of the entropy versus energy) formulas will prompt
the spinodal region through specific signals. Finally, the same microcanonical
formulas are deduced for the case when an incomplete number of fragments per
event are available. These formulas could overcome the freeze-out backtracking
deficiencies.Comment: accepted to Nuclear Physics
Recommended from our members
Proton irradiation of EMCCDs
This paper describes the irradiation of 95 electron multiplication charge coupled devices (EMCCDs) at the Paul Scherrer Institut (PSI) in Switzerland, to investigate the effects of proton irradiation on the operational characteristics of CCDs featuring electron multiplication technology for space use. This work was carried out in support of the CCD development for the radial velocity spectrometer (RVS) instrument of the European Space Agency's cornerstone Gaia mission. Previous proton irradiations of EMCCDs, have shown the technology to be radiation hard to /spl sim/10/spl times/ the required six-year Gaia lifetime proton fluence, with no device failures or unexpected operational changes. The purpose of the study described in this paper was to further investigate the statistical probability of device failure as a result of radiation damage, the large number of devices and high proton fluence used, making the study equivalent to testing /spl sim/50 complete RVS CCD focal planes to the expected end of life proton dose. An outline of the earlier EMCCD proton irradiations is given, followed by a detailed description of the proton irradiation and characterization of the 95 devices used in this latest study
Quantum thermodynamics at critical points during melting and solidification processes
We systematically explore and show the existence of finite-temperature
continuous quantum phase transition (CTQPT) at a critical point, namely, during
solidification or melting such that the first-order thermal phase transition is
a special case within CTQPT. Infact, CTQPT is related to chemical reaction
where quantum fluctuation (due to wavefunction transformation) is caused by
thermal energy and it can occur maximally for temperatures much higher than
zero Kelvin. To extract the quantity related to CTQPT, we use the ionization
energy theory and the energy-level spacing renormalization group method to
derive the energy-level spacing entropy, renormalized Bose-Einstein
distribution and the time-dependent specific heat capacity. This work
unambiguously shows that the quantum phase transition applies for any finite
temperatures.Comment: To be published in Indian Journal of Physics (Kolkata
Thermodynamics of baryonic matter with strangeness within non-relativistic energy density functional model
We study the thermodynamical properties of compressed baryonic matter with
strangeness within non-relativistic energy density functional models with a
particular emphasis on possible phase transitions found earlier for a simple
-mixture. The aim of the paper is twofold: I) examining the
phase structure of the complete system, including the full baryonic octet and
II) testing the sensitivity of the results to the model parameters. We find
that, associated to the onset of the different hyperonic families, up to three
separate strangeness-driven phase transitions may occur. Consequently, a large
fraction of the baryonic density domain is covered by phase coexistence with
potential relevance for (proto)-neutron star evolution. It is shown that the
presence of a phase transition is compatible both with the observational
constraint on the maximal neutron star mass, and with the present experimental
information on hypernuclei. In particular we show that two solar mass neutron
stars are compatible with important hyperon content. Still, the parameter space
is too large to give a definitive conclusion of the possible occurrence of a
strangeness driven phase transition, and further constraints from
multiple-hyperon nuclei and/or hyperon diffusion data are needed.Comment: 11 pages, 7 figure
Break-up fragment topology in statistical multifragmentation models
Break-up fragmentation patterns together with kinetic and configurational
energy fluctuations are investigated in the framework of a microcanonical model
with fragment degrees of freedom over a broad excitation energy range. As far
as fragment partitioning is approximately preserved, energy fluctuations are
found to be rather insensitive to both the way in which the freeze-out volume
is constrained and the trajectory followed by the system in the excitation
energy - freeze-out volume space. Due to hard-core repulsion, the freeze-out
volume is found to be populated un-uniformly, its highly depleted core giving
the source a bubble-like structure. The most probable localization of the
largest fragments in the freeze-out volume may be inferred experimentally from
their kinematic properties, largely dictated by Coulomb repulsion
- âŠ