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Ad. R. Raduta

Publications and source records attributed to Ad. R. Raduta.

48 records · Page 3Linked to original sources
arXiv2005

Fragment isospin distributions and the phase diagram of excited nuclear systems

Fragment average isospin distributions are investigated within a microcanonical multifragmentation model in different regions of the phase diagram. The results indicate that in the liquid phase $ $ versus $Z$ is monotonically increasing, in the phase coexistence region it has a rise and fall shape and in the gas phase it is constant. Deviations from this behavior may manifest at low fragment multiplicity as a consequence of mass/charge conservation. Characterization of the "free" and "bound" phases function of fragment charge reconfirms the neutron enrichment of the "free" phase with respect to the "bound" one irrespectively the localization of the multifragmentation event in the phase diagram.

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arXiv2005

Break-up fragments excitation and the freeze-out volume

We investigate, in microcanonical multifragmentation models, the influence of the amount of energy dissipated in break-up fragments excitation on freeze-out volume determination. Assuming a limiting temperature decreasing with nuclear mass, we obtain for the Xe+Sn at 32 MeV/nucleon reaction [J. D. Frankland et al., Nucl. Phys. A689, 905 (2001); A689, 940 (2001)] a freeze-out volume almost half the one deduced using a constant limiting temperature.

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arXiv2005

Kinetic energy spectra for fragments and break-up density in multifragmentation

We investigate the possibility, in nuclear fragmentation, to extract information on nuclear density at break-up from fragment kinetic energy spectra using a simultaneous scenario for fragment emission. The conclusions we derive are different from the recently published results of Viola et al. [Phys. Rev. Lett. 93, (2004), 132701] assuming a sequential fragment emission and claiming that the experimentally observed decrease of peak centroids for kinetic energy spectra of fragments with increasing bombarding energy is due to a monotonic decrease of the break-up density.

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arXiv2004

Microcanonical studies on isoscaling

The exponential scaling of isotopic yields is investigated for sources of different sizes over a broad range of excitation energies and freeze-out volumes, in both primary and asymptotic stages of the decay in the framework of a microcanonical multifragmentation model. It was found that the scaling parameters have a strong dependence on the considered pair of equilibrated sources and excitation energy and are affected by the secondary particle emission of the break-up fragments. No significant influence of the freeze-out volume on the considered isotopic ratios has been observed. Deviations of microcanonical results from grandcanonical expectations are discussed.

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arXiv2003

The influence of Coulomb on the liquid-gas phase transition and nuclear multifragmentation

The liquid-gas phase transition is analyzed from the topologic properties of the event distribution in the obervables space. A multi-canonical formalism allows to directly relate the standard phase transition with neutral particles to the case where the non saturating Coulomb interaction is present, and to interpret the effect of Coulomb as a deformation of the probability distributions and a rotation of the order parameter. This formalism is applied to a statistical multifragmentation model and consequences for the nuclear multifragmentation phase transitions are drawn.

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arXiv2003

Homogeneity and Size Effects on the Liquid-Gas Coexistence Curve

The effects of (in)homogeneity and size on the phase diagram of Lennard-Jones fluids are investigated. It is shown that standard multifragmentation scenarios (finite equilibrated systems with conserved center of mass position and momentum) are implying a strong radial inhomogeneity of the system strongly affecting the phase diagram. The homogeneity constraint is therefore necessary for finite systems in order to align to the ``meaning'' of infinite systems phase diagrams. In this respect, a method which deduces the equation of state of homogeneous finite systems from the one corresponding to bulk matter is designed. The resultant phase diagrams show a strong dependence on the system's size.

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arXiv2002

Searching for the statistically equilibrated systems formed in heavy ion collisions

Further improvements and refinements are brought to the microcanonical multifragmentation model [Al. H. Raduta and Ad. R. Raduta, Phys. Rev. C {\bf 55}, 1344 (1997); {\it ibid.} {\bf 61}, 034611 (2000)]. The new version of the model is tested on the recently published experimental data concerning the Xe+Sn at 32 MeV/u and Gd+U at 36 MeV/u reactions. A remarkable good simultaneous reproduction of fragment size observables and kinematic observables is to be noticed. It is shown that the equilibrated source can be unambiguously identified.

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arXiv2001

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.

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arXiv2000

Effects of the secondary decays on the isotopic thermometers

The sharp microcanonical multifragmentation model from [Al. H. Raduta and Ad. R. Raduta, Phys. Rev. C 55, 1344 (1997); Phys. Rev. C, in press] is employed for evaluating the nuclear caloric curve predictions of nine isotopic thermometers for three representative nuclei. Evaluations are performed for both primary decay and asymptotic stages. Effects of the secondary decays on the primary decay caloric curves are evidenced and discussed. In both cases a dispersive character of the isotopic caloric curves with increasing the source excitation energy is observed. A procedure of calibrating the isotopic thermometers on the microcanonical predictions for both primary decay and asymptotic stages is proposed. The resulting set of calibrating parameters for each thermometer is independent on the source size, on its excitation energy and, in the case of the primary decay, on the freeze-out radius assumption.

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arXiv1999

Microcanonical studies concerning the recent experimental evaluations of the nuclear caloric curve

The microcanonical multifragmentation model from [Al. H. Raduta and Ad. R. Raduta, Phys. Rev. C 55, 1344 (1997); 56, 2059 (1997); 59, 323 (1999)] is refined and improved by taking into account the experimental discrete levels for fragments with $A \le 6$ and by including the stage of sequential decay of the primary excited fragments. The caloric curve is reevaluated and the heat capacity at constant volume curve is represented as a function of excitation energy and temperature. The sequence of equilibrated sources formed in the reactions studied by the ALADIN group ($^{197}$Au+$^{197}$Au at 600, 800 and 1000 MeV/nucleon bombarding energy) is deduced by fitting simultaneously the model predicted mean multiplicity of intermediate mass fragments ($M_{IMF}$) and charge asymmetry of the two largest fragments ($a_{12}$) versus bound charge ($Z_{bound}$) on the corresponding experimental data. Calculated HeLi isotopic temperature curves as a function of the bound charge are compared with the experimentally deduced ones.

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