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

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.Comment: 13 pages, 4 figure

Collective dipole excitations in sodium clusters

Some properties of small and medium sodium clusters are described within the RPA approach using a projected spherical single particle basis. The oscillator strengths calculated with a Schiff-like dipole transition operator and folded with Lorentzian functions are used to calculate the photoabsorbtion cross section spectra. The results are further employed to establish the dependence of the plasmon frequency on the number of cluster components. Static electric polarizabilities of the clusters excited in a RPA dipole state are also calculated. Comparison of our results with the corresponding experimental data show an overall good agreement.Comment: 23 pages, 5 figure

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.Comment: Physical Review C, in pres

Simultaneous description of four positive and four negative parity bands

The extended coherent state model is further extended in order to describe two dipole bands of different parities. The formalism provides a consistent description of eight rotational bands. A unified description for spherical, transitional and deformed nuclei is possible. Projecting out the angular momentum and parity from a sole state, the $K^{\pi}=1^+$ band acquires a magnetic character, while the electric properties prevail for the other band. Signatures for a static octupole deformation in some states of the dipole bands are pointed out. Some properties which distinguish between the dipole band states and states of the same parity but belonging to other bands are mentioned. Interesting features concerning the decay properties of the two bands are found. Numerical applications are made for $^{158}$Gd, $^{172}$Yb, $^{228,232}$Th, $^{226}$Ra, $^{238}$U and $^{238}$Pu, and the results are compared with the available data.Comment: 36 pages, 13 figures, 12 table

Liquid-gas phase transition in nuclear multifragmentation

The equation of state of nuclear matter suggests that at suitable beam energies the disassembling hot system formed in heavy ion collisions will pass through a liquid-gas coexistence region. Searching for the signatures of the phase transition has been a very important focal point of experimental endeavours in heavy ion collisions, in the last fifteen years. Simultaneously theoretical models have been developed to provide information about the equation of state and reaction mechanisms consistent with the experimental observables. This article is a review of this endeavour.Comment: 63 pages, 27 figures, submitted to Adv. Nucl. Phys. Some typos corrected, minor text change

New type of chiral motion in even–even nuclei: the 138^{138}Nd case

International audienceThe phenomenological generalized coherent state model Hamiltonian is amended with a many body term describing a set of nucleons moving in a shell model mean-field and interacting among themselves with pairing, as well as with a particle–core interaction of spin–spin type. The model Hamiltonian is treated in a restricted space consisting of the core projected states associated to the band ground, $\beta ,\gamma ,\widetilde{\gamma },{1}^{+}$ and $\widetilde{{1}^{+}}$ and two proton aligned quasiparticles coupled to the states of the collective dipole band. The chirally transformed particle–core states are also included. The Hamiltonian contains two terms which are not invariant to the chiral transformations relating the right-handed frame $({{\bf{J}}}_{{\bf{F}}},{{\bf{J}}}_{{\bf{p}}},{{\bf{J}}}_{{\bf{n}}})$ and the left-handed ones $(-{{\bf{J}}}_{{\bf{F}}},{{\bf{J}}}_{{\bf{p}}},{{\bf{J}}}_{{\bf{n}}})$, $({{\bf{J}}}_{{\bf{F}}},-{{\bf{J}}}_{{\bf{p}}},{{\bf{J}}}_{{\bf{n}}})$, $({{\bf{J}}}_{{\bf{F}}},{{\bf{J}}}_{{\bf{p}}},-{{\bf{J}}}_{{\bf{n}}})$ where ${{\bf{J}}}_{{\bf{F}}},{{\bf{J}}}_{{\bf{p}}},{{\bf{J}}}_{{\bf{n}}}$ are the angular momenta carried by fermions, proton and neutron bosons, respectively. The energies defined with the particle–core states form four bands, two of them being degenerate in the present formalism, while the other two exhibit chiral properties reflected by energies, electromagnetic properties and the energy staggering function. A numerical application for (138)Nd shows a good agreement between results and the corresponding experimental data