Fragment size correlations in finite systems - application to nuclear multifragmentation

We present a new method for the calculation of fragment size correlations in a discrete finite system in which correlations explicitly due to the finite extent of the system are suppressed. To this end, we introduce a combinatorial model, which describes the fragmentation of a finite system as a sequence of independent random emissions of fragments. The sequence is accepted when the sum of the sizes is equal to the total size. The parameters of the model, which may be used to calculate all partition probabilities, are the intrinsic probabilities associated with the fragments. Any fragment size correlation function can be built by calculating the ratio between the partition probabilities in the data sample (resulting from an experiment or from a Monte Carlo simulation) and the 'independent emission' model partition probabilities. This technique is applied to charge correlations introduced by Moretto and collaborators. It is shown that the percolation and the nuclear statistical multifragmentaion model ({\sc smm}) are almost independent emission models whereas the nuclear spinodal decomposition model ({\sc bob}) shows strong correlations corresponding to the break-up of the hot dilute nucleus into nearly equal size fragments

Correlations in Nuclear Arrhenius-Type Plots

Arrhenius-type plots for multifragmentation process, defined as the transverse energy dependence of the single-fragment emission-probability, -ln(p_{b}) vs 1/sqrt(E_{t}), have been studied by examining the relationship of the parameters p_{b} and E_{t} to the intermediate-mass fragment multiplicity . The linearity of these plots reflects the correlation of the fragment multiplicity with the transverse energy. These plots may not provide thermal scaling information about fragment production as previously suggested.Comment: 12 pages, Latex, 3 Postscript figures include

The Relationship Between Cusp Region Ion Outflows and East-West Magnetic Field Fluctuations at 4,000-km Altitude

A number of interdependent conditions and processes contribute to ionospheric-origin energetic ( 10 eV to several keV) ion outflows. Due to these interdependences and the associated observational challenges, energetic ion outflows remain a poorly understood facet of atmosphere-ionosphere-magnetosphere coupling. Here we demonstrate the relationship between east-west magnetic field fluctuations ( ) and energetic outflows in the magnetosphere-ionosphere transition region. We use dayside cusp region FAST satellite observations made near apogee ( 4,180-km altitude) near fall equinox and solstices in both hemispheres to derive statistical relationships between ion upflow and spectral power as a function of spacecraft frame frequency bands between 0 and 4 Hz. Identification of ionospheric-origin energetic ion upflows is automated, and the spectral power in each frequency band is obtained via integration of power spectral density. Derived relationships are of the form for upward ion flux at 130-km altitude, with the mapped upward ion flux for a nominal spectral power nT . The highest correlation coefficients are obtained for spacecraft frame frequencies 0.1–0.5 Hz. Summer solstice and fall equinox observations yield power law indices 0.9–1.3 and correlation coefficients , while winter solstice observations yield 0.4–0.8 with . Mass spectrometer observations reveal that the oxygen/hydrogen ion composition ratio near summer solstice is much greater than the corresponding ratio near winter. These results reinforce the importance of ion composition in outflow models. If observed perturbations result from Doppler-shifted wave structures with near-zero frequencies, we show that spacecraft frame frequencies 0.1–0.5 Hz correspond to perpendicular spatial scales of several to tens of kilometers

A statistical interpretation of the correlation between intermediate mass fragment multiplicity and transverse energy

Multifragment emission following Xe+Au collisions at 30, 40, 50 and 60 AMeV has been studied with multidetector systems covering nearly 4-pi in solid angle. The correlations of both the intermediate mass fragment and light charged particle multiplicities with the transverse energy are explored. A comparison is made with results from a similar system, Xe+Bi at 28 AMeV. The experimental trends are compared to statistical model predictions.Comment: 7 pages, submitted to Phys. Rev.

Isospin relaxation time in heavy-ion collisions at intermediate energies

Using an isospin-dependent transport model, we have studied the isospin and momentum relaxation times in the heavy residues formed in heavy-ion collisions at intermediate energies. It is found that only at incident energies below the Fermi energy, chemical or thermal equilibrium can be reached before dynamical instability is developed in the heavy residues. Also, the isospin relaxation time is shorter (longer) than that for momentum at beam energies lower (higher) than the Fermi energy.Comment: 8 pages Latex + 2 ps Figs.; Phys. Rev. C in pres

Multifragmentation of non-spherical nuclei

The shape influence of decaying thermalized source on various characteristics of multifragmentation as well as its interplay with effects of angular momentum and collective expansion are first studied and the most pertinent variables are proposed. The analysis is based on the extension of the statistical microcanonical multifragmentation model.Comment: 5 pages, 4 figure

The three-dimensional Ising model: A paradigm of liquid-vapor coexistence in nuclear multifragmentation

Clusters in the three-dimensional Ising model rigorously obey reducibility and thermal scaling up to the critical temperature. The barriers extracted from Arrhenius plots depend on the cluster size as $B \propto A^{\sigma}$ where $\sigma$ is a critical exponent relating the cluster size to the cluster surface. All the Arrhenius plots collapse into a single Fisher-like scaling function indicating liquid-vapor-like phase coexistence and the univariant equilibrium between percolating clusters and finite clusters. The compelling similarity with nuclear multifragmentation is discussed.Comment: (4 pages, 4 figures

Time-Dependent Hartree-Fock simulation of the expansion of abraded nuclei

A recent interpretation of the caloric curve based on the expansion of the abraded spectator nucleus is re-analysed in the framework of the Time-Dependent Hartree-Fock (TDHF) evolution. It is shown that the TDHF dynamics is more complex than a single monopolar collective motion at moderate energy. The inclusion of other important collective degrees of freedom may lead to the dynamical creation of hollow structure. Then, low density regions could be locally reached after a long time by the creation of these exotic density profiles. In particular the systematic of the minimum density reached during the expansion (the so-called turning points) appears to be different.Comment: 30 Latex pages including 9 figure

Coulomb effects on growth of instabilities in asymmetric nuclear matter

We study the effects of the Coulomb interaction on the growth of unstable modes in asymmetric nuclear matter. In order to compare with previous calculations we use a semiclassical approach based on the linearized Vlasov equation. Moreover, a quantum calculation is performed within the R.P.A.. The Coulomb effects are a slowing down of the growth and the occurrence of a minimal wave vector for the onset of the instabilities. The quantum corrections cause a further decrease of the growth rates.Comment: 10 pages, revtex, 4 ps figures, to appear in Phys. Rev. C e-mail: [email protected], [email protected]

Critical temperature for the nuclear liquid-gas phase transition (from multifragmentation and fission)

Critical temperature Tc for the nuclear liquid-gas phase transition is stimated both from the multifragmentation and fission data. In the first case,the critical temperature is obtained by analysis of the IMF yields in p(8.1 GeV)+Au collisions within the statistical model of multifragmentation (SMM). In the second case, the experimental fission probability for excited 188Os is compared with the calculated one with Tc as a free parameter. It is concluded for both cases that the critical temperature is higher than 16 MeV.Comment: 15 pages, 8 figure