Nuclear Physics at Border Lines

CONFERENCE ORGANIZATION AND COMMITTEES.

ACKNOWLEDGMENTS.

PREFACE.

CONTENTS.

The properties of neutron-rich nuclei near the drip-line are considered for two limiting cases: for the lightest elements, namely isotopes of hydrogen with A=4-5 and superheavy elements with A=288 and 292. The isotopes of ⁴H and ⁵H have been investigated using the 58 MeV triton beam in the reactions t+d and t+t with registering charged particles and neutrons. In the spectra of the excitation energies certain states have been found which determine the structural properties of these nuclei. A programme of further investigations with the use of the accelerator complex of radioactive beams DRIBs, which is being created at the moment, is discussed. Characteristics of beams of radioactive ions with light and medium masses, which are expected to be yielded using DRIBs after its commissioning, are presented.

Results on the synthesis of even-even isotopes with Z=l10-116 in reactions with ⁴⁸Ca ions are discussed. It is shown that an increase in the neutron numbers of heavy nuclei greatly enhances their stability in respect to α-decay and spontaneous fission. Radioactive properties of the new nuclides confirm theoretical predictions concerning the existence of the "islands of stability" of superheavy nuclei.

Thermal photons have been used as a clock to determine the time of IMF emission during the evolution of the nuclear reaction. The method has been applied to the reaction ⁵⁸Ni + ¹⁹⁷Au at 30 and 45 MeV/amu incident energy. The results put in evidence that the relative contribution of the two possible production mechanisms (dynamical and statistical) is quite different in the two cases. A comparison with theoretical calculations strongly supports the experimental findings.

γ-ray spectra in coincidence with charged particles for the reactions ⁴⁰Ca+ ⁴⁸Ca, ⁴⁶Ti at E_inc=25 A MeV are presented. The spectra statistical analysis shows the survival of the GDR up to excitation energy around 4 MeV/A for a system with mass of 50-60 amu. This result was obtained by improving statistical calculations by including the deuteron decay channel, the mass dependence of the GDR parameters in the decay chain, and the GDR isospin splitting.

The experimental spectroscopy of very-neutron-rich nuclei adds a new dimension to our understanding of nuclear structure. In this contribution, a description of the multi-detector for β-delayed neutron spectroscopy TONNERRE is presented. Following a brief discussion of the motivations behind the project and the design of the array, some perspectives concerning future physics directions are proposed. An example which illustrates the physics capabilities of TONNERRE, namely the neutron energy spectrum in the β-decay of ³⁴Al obtained with this array, is shown.

We study the reactions ³H(³H, 2n)⁴He and ³He(³He, 2p)⁴He within a fully microscopic cluster model coupling two- and three-cluster configurations and featuring a three-cluster exit channel. The three-cluster continuum is described by Hyperspherical Harmonics. The dynamical equations are solved by the Modified J-Matrix Method, which includes potential asymptotic information for fast convergence. The resulting astrophysical S-factor of both reactions is in good agreement with experimental data.

No abstract received.

In this short review the main experimental results which, about one year ago, were pointed out as a "compelling evidence" of the formation of a new state of matter at the SPS energies are discussed. In particular, the last SPS results about strangeness enhancement and J/ψ suppression are summarized.

Recent improvements in the intensities and optical qualities of radioactive ion beams have made possible the study of direct reactions induced by unstable nuclei. The design and performances of an innovative silicon strip detector array devoted to such studies are described. Elastic and inelastic proton scattering are used to obtain information on density and transition density distributions of exotic nuclei. The structure of the wave functions of halo nuclei can be probed through transfer and knock-out reactions. Achievements in these investigations are illustrated with recent experimental results.

Interest in the study of the fission process of superheavy nuclei interactions with heavy ions is connected first of all with the possibility of obtaining information, the most important for the problem of synthesis on the production cross section of compound nuclei at excitation energies of about 15-30 MeV. There is a need for a much more penetrating insight into the fission mechanism of superheavy nuclei. Reaction ⁵⁸Fe + ²⁴⁸Cm leads to the formation of the heaviest compound system ever studied, namely ³⁰⁶122 (N=184), i.e. to the formation of the spherical compound nucleus, which agrees well with theoretical predictions [1]. Actually, three ⁵⁸Fe ion beam induced reactions were taken into account to compare the experimental data: ⁵⁸Fe+²³²Th → ²⁹⁰116, ⁵⁸Fe+²⁴⁴Pu →³⁰²120, ⁵⁸Fe + ²⁴⁸Cm → ³⁰⁶122.

A new shape isomer in the N=Z ⁷²Kr nucleus has been observed at GANIL with a combined conversion electron and γ-ray spectroscopy. This low-lying 0⁺ state is clear evidence for shape coexistence as expected from theoretical calculations. The ground state is interpreted as a pure oblate state.

The (⁷Li,⁷Be) charge exchange reaction is performed at low bombarding energy as a probe for spectroscopy of light exotic nuclei. The high resolution experimental technique is based on the interplay of a Tandem Van de Graaf ⁷Li beam and a magnetic spectrometer. Results are discussed for ¹¹B(⁷Li,⁷Be)¹¹Be, ¹⁵N(⁷Li,⁷Be)¹⁵C and ¹⁴C (⁷Li,⁷Be)¹⁴B reactions at 57 MeV.

We discuss some properties of instabilities in asymmetric nuclear matter, underlying in particular the link between the nature of unstable fluctuations and the properties of the interaction. We show that, conversely to what happens in symmetric nuclear matter, chemical instabilities may appear as isoscalar-like unstable oscillations, similarly to mechanical instabilities, leading to the formation of a more symmetric liquid phase, surrounded by a neutron rich gas phase. Then we present numerical simulations of multifragmentation processes in asymmetric nuclear matter and in central heavy ion collisions at intermediate energies. In the same context, but in the case of semi-peripheral reactions, the dynamics of the so-called neck region is discussed.

The fragment separator FRS(GSI) was used to measure longitudinal momentum distributions and one-nucleon removal cross-sections of relativistic fragments after breakup for different secondary beams in coincidence with gamma rays from the de-excitation of those fragments. The combination of in-beam gamma spectroscopy at relativistic energies with secondary nuclear reactions has added new information that will help us to better understand the ground state properties (definite assignment of spins and parities of the ground state) of the exotic nuclei. The proton-rich isotope ⁸B is presented as a test case to show the power of the experimental technique. New experimental results on momentum distributions and one-nucleon removal cross-sections in coincidence with gamma ray detection for N, O and F isotopes will also be discussed.

The ^9,10,11Be nuclei are described in a microscopic multicluster model involving α+α+n, α+α+n+n and α+α+n+n+n configurations, respectively. The effect of α clustering is shown to decrease from ⁹Be to ¹¹Be. A discussion of the band structure is presented. In ¹¹Be, the existence of a 3/2^- band, suggested recently, is not supported by the model.

We present a survey of experimental results obtained at GANIL (Caen, France) resulting in an appearance of a new magic number, N=16, in very neutron-rich nuclei. Two neutron separation energies derived from recent mass measurements of neutron-rich nuclei together with the measurements of instability of the doubly magic nucleus ²⁸O give a very clear evidence for the existence of the new shell closure N=16. This shell appears between 2s_1/2 and 1d_3/2 neutron orbitals for neutron-rich nuclei from carbon to neon.

A dynamical model of fission fragment angular distributions is suggested. The model allows one to calculate fission fragment angular distributions, prescission light particle multyplicities, evaporation residue cross sections etc. for the cases of decay of hot and rotating heavy nuclei. The experimental data on angular anisotropies of fission fragments and prescission neutron multiplicities are analyzed for the ¹⁶O + ²⁰⁸Pb, ²³²Th, ²⁴⁸Cm and ²³⁸U reactions at the energies of the incident ¹⁶O ions ranging from 90 to 160 MeV. This analysis allows us to extract both the nuclear friction coefficient value and the relaxation time for the tilting mode. It is also demonstrated that the angular distributions are sensitive to the deformation dependence of the nuclear friction.

The reaction ⁶He+⁶⁴Zn was studied in order to investigate the effects of the halo structure on the fusion cross-section at low bombarding energy. The evaporation residues were identified by measuring off-line the X-ray emission which follows their Electron Capture decay. The reaction ⁴He+⁶⁴Zn was also measured and the results are presented.

Major new opportunities for research with beams of rare isotopes in the United States will be discussed. For the near term future, the new Coupled Cyclotron Facility (CCF) at the National Superconducting Cyclotron Laboratory (NSCL) will provide fast beams of rare isotopes with intensities higher by about 3 orders of magnitude than previously available in the U.S. The scope of the CCF construction project, the planned facility layout, and key research questions that can be addressed with fast beams of rare isotopes will be presented. On a longer time scale, large additional gains, especially for medium-mass and heavy elements, will be possible with the Rare Isotope Accelerator (RIA) now under discussion. The writing group for the new (2001) long-range plan for nuclear science in the United States has recommended construction of RIA as its highest priority for new construction. Main features of the RIA concept will be highlighted.

In quaternary fission the two fission fragments are accompanied by two light charged particles (LCP). The process has been studied for ²³³U(n,f) and ²³⁵U(n,f) induced by cold neutrons. For (α,α) and (α,τ) as LCPs true and pseudo quaternary fission are disentangled. In true quaternary fission the LCPs are born right at scission, while the pseudo process is mediated by the particle-unstable ternary isotopes ⁸Be and ⁷Li*, respectively.

A new apparatus has been designed and built to study reaction mechanisms in the energy regime of the ALPI linear accelerator of the Laboratori Nazionali di Legnaro (E/A = 5 - 20 MeV). In this paper the importance of studying these mechanisms will be underlined, no more as a problem limited to a narrow energy range or a single process, but as a continuous trend from low to high energies and from the physics of stable nuclei to that one regarding instabilities. With this remarks in mind, a first experiment has been performed studying the reaction ³²S+⁵⁸Ni at 11AMeV. Preliminary results show that important information can be derived on multi-body emission, which can contribute to renew the interest in this energy regime.

Several methods based on effective interactions or Lagrangians are available today. Although different in many respects (use of zero range or finite range interactions, relativistic or non relativistic framework, different treatments of pairing correlations), their applications to super heavy nuclei have shown converging results which still have to be incorporated in macroscopic approaches. Many efforts are also actually devoted to the improvements of the effective interactions, especially of the pairing force. I shall review the main results obtained thanks these methods in the last years.

The nuclear shell model predicts that the next doubly magic shell-closure beyond ²⁰⁸Pb is at a proton number between Z = 114 and 126 and at a neutron number Z = 184. The outstanding aim of experimental investigations is the exploration of this region of spherical 'SuperHeavy Elements' (SHEs). This article describes the experiments that were performed at the GSI SHIP. They resulted in an unambiguous identification of elements 107 to 112. They were negative so far in searching for elements 113, 116 and 118. The measured decay data are compared with theoretical predictions. Some aspects concerning the reaction mechanism are also presented.

The work presents the results of the study of neutron emission characteristics in the fission and quasi-fission of heavy nuclei, produced in the reactions with ⁴⁸Ca ions. These experiments have been performed at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) with the use of the time-of-flight spectrometer of fission fragments CORSET and neutron multidetector DEMON. ²⁰⁸Pb, ²³²Th and ²⁴⁸Cm layers 120-200 mkg/cm² in thickness were used as targets. The mass and energy distributions of the fission fragments, the multiplicities of pre- and post-fission neutrons at energies close to the Coulomb barrier have been measured. The analysis of neutron energy and angular distributions has shown that the total neutron multiplicity M_tot in the fusion-fission reactions of compound nuclei formed in the reactions with heavy ions is essentially higher than M_tot in the quasi-fission reactions. Note that M_tot monotonously increases with the growing Z of the compound nucleus.

The process of fusion-fission of superheavy nuclei with Z=102-122 formed in the reactions with ²²Ne, ²⁶Mg, ⁴⁸Ca, ⁵⁸Fe and ⁸⁶Kr ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) using a time-of-flight spectrometer of fission fragments CORSET and a neutron multi-detector DEMON. As a result of the experiments, mass and energy distributions of fission fragments, fission and quasi-fission cross sections, multiplicities of neutrons and gamma-quanta and their dependence on the mechanism of formation and decay of compound superheavy systems have been studied.

This work is devoted to the investigation of characteristics of neutron and gamma emission in the processes of fission and quasi-fission of the compound nuclei ²⁵⁶No, ²⁷⁰Sg, ²⁶⁶Hs, ²⁷¹Hs, ²⁷⁴Hs, ²⁸⁶112, ²⁹²114, ²⁹⁶116, ³⁰²120 and ³⁰⁶122, produced in reactions with ions ²⁶Mg, ⁴⁸Ca, ⁵⁸Fe at energies close to and below the Coulomb barrier (i.e. when the influence of the shell effects on the fusion and on the characteristics of the decay of the composite system is considerable). The major part of these experiments has been performed at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Dubna) and also at the SARA accelerator of the Institut des Sciences Nucleaires (Grenoble, France) using a time-of-flight spectrometer of fission fragments CORSET (CORrelation SET-up) [1] and a neutron multi-detector DEMON [2]. The analysis of energy and angular distributions of neutrons and gamma quanta has shown that the < M^FF_γ > value for the fusion-fission process is greater than the value of < M^QF_γ > for the quasi-fission process, and on the other hand, the total neutron multiplicity M_tot and total gamma-multiplicity < M_γ > monotonously increase with the atomic number Z of the compound nucleus as well as with the bombarding energy.

Laser spectroscopy measurements have been carried out on the very-neutron-rich tin isotope with the COMPLIS experimental setup. Using the 5s²5p^{2 3}P₀ → 5s²5p6s³P₁ optical transition, hyperfine spectra of ^126-132Sn and ^{125m, 127m, 129m-131m}Sn where recorded for the first time. The variation of the mean square charge radius (δ< r² >) between these nuclei and nuclear moments of the isomers and the odd isotopes were thus measured. An odd even staggering which inverts at A=130 is clearly observed. This indicates a small appearance of a plateau on the δ< r² > which should be confirmed by measuring the isotope shift beyond A=132.

The structure of nuclei far off β-stability is investigated by nuclear many-body theory. In-medium interactions for asymmetric nuclear matter are obtained by (Dirac-) Brueckner theory thus establishing the link of nuclear forces to free space interactions. HFB and RPA theory is used to describe ground and excited states of nuclei from light to heavy masses. In extreme dripline systems pairing and core polarization are found to be most important for the binding, especially of halo nuclei. The calculations show that far off stability mean-field dynamics is gradually replaced by dynamical correlations, giving rise to the dissolution of shell structures.

New developments in ion cooling and ion bunching allow the trapping of radioactive ions from a low energy beam, in a very short time-scale and with very good efficiency. In the present work, we intend to use a RFQ device to inject ⁶He⁺ ions in a transparent Paul trap in order to study the β decay spectrum. The ion beam will be delivered by the future low energy beam line of the SPIRAL facility at GANIL. The cooling of the beam before injection into the trap will be achieved by the use of a H² buffer gas in the RFQ, for which simulations give a 10% transmission. In the Paul trap, the ions will be in vacuum and nearly at rest, allowing a careful measurement of the β - recoil ion coincidence spectrum. These data will be sensitive to the angular correlation parameter "a", which depends on the coupling constants of the weak hamiltonian. It should be equal to -1/3 if the interaction is only of Axial vector type (V-A theory). Deviation from this value would imply a new Tensor-like interaction leading to new physics beyond the Standard Model.

Glass track detectors and the crystal blocking method have been used to measure time delays associated with the production of fission fragments in the reaction induced by 30 MeV α particles on a 235UO₂ crystal. Tracks have been read by an automatic, computer driven, microscope. Preliminary results indicate a possible long-lifetime component, as suggested by recent theories.

An experimental programme aiming to probe correlations in two-neutron halo nuclei is presented. Three different techniques have been applied to the three well-established systems, ⁶He, ¹¹Li and ¹⁴Be: intensity interferometry following the dissociation, radiative capture of high-energy protons, and the study of three-particle correlations in the β-n-n decay. The results of the different experiments, as well as the combination of them, provide an important step forward in the knowledge of the correlations within these Borromean systems, as for example the relative distance between neutrons in the halo.

Projectile fragmentation associated with γ-ray spectroscopy has been used to populate and study isomeric states of very neutron-rich nuclei in the transitional region with A~190-200. This experiment has proven the ability of such a technique to populate medium to high spin states and γ-ray transitions have been observed for the first time in a number of neutron-rich nuclei, including ¹⁹⁰W, ¹⁹⁵Os, ¹⁹⁷Ir, ²⁰²Pt.

Large α production cross sections were measured for the systems ^6,7Li+²⁰⁸Pb; they were identified with the total breakup cross sections. A theoretical description based on coupled channels method, also including coupling to a discretized continuum, underestimates the experimental data. These large cross sections, also found for the systems ⁶He,⁹Be+²⁰⁹Bi, originate from the low binding energies of these light nuclei. The total reaction cross sections for these systems, deduced from the elastic scattering, coincide with the fusion + breakup ones.

The leptodermous approximation is applied to nuclear systems for T > 0. The introduction of surface corrections leads to anomalous caloric curves and to negative heat capacities in the liquid-gas coexistence region. Clusterization in the vapor is described by associating surface energy to clusters according to Fisher's formula. The three-dimensional Ising model, a leptodermous system par excellence, does obey rigorously Fisher's scaling up to the critical point. The ISiS multifragmentation data follows the same scaling, thus providing the strongest evidence yet of liquid-vapor coexistence.

For actinide nuclei, as well as for superheavy nuclei, low-energy asymmetric fission results from clusterization phenomena. The role of a primordial diclusteric configuration, first suggested by the mean-mass laws of Wahl, is confirmed by a new relation describing both actinide and superheavy nuclei and independent of the mean-mass concept. New properties of the asymmetric mode of the superheavy nuclei are put into evidence.

We reanalyze the astrophysical S-factor for ¹³C(p, γ)¹⁴N capture using the R-matrix approach. The low-energy S factor is dominanted by two resonant and nonresonant captures. The normalization of the nonresonant term for the transition to a particular bound state of the final nucleus is expressed in terms of the corresponding asymptotic normalization coefficient (ANC). In the analysis we use the ANC's inferred from ¹⁴N(¹³C, ¹⁴N)¹⁴C and ¹³C(³He,d)¹⁴N reactions. The fit of the calculated S factor to the experimental one turns out to be sensitive to the ANC's values and is a test of the ANC's determined by us. The total calculated S-factor at zero energy, S(0) = 7.65 keVb, is in an excellent agreement with the value of 7.64 keVb determined earlier ¹.

The ⁶Li(⁶Li,αα)⁴He reaction has been studied in a kinematically complete experiment at E_6Li = 6 MeV, from which indirect evaluation of the ⁶Li(d,α)⁴He bare nucleus cross section was extracted by means of the Trojan Horse Method (THM). A new theoretical description, based on the DWBA approach, allows to extract information on the bare astrophysical S-factor, and therefore on the electron screening U_e. Both projectile and target break-up were analyzed and used to extract the averaged S(E)-factor. The results are compared with direct experimental data leading to a model independent value of the electron screening potential energy, U_e = 320 ± 50 eV, much higher than the adiabatic limit U_ad= 175 eV.

For the study of halo structure in neutron-rich He and Li isotopes, experiments on proton elastic scattering from ^4,6,8He and ^6,8,9,11Li nuclei were performed in inverse kinematics. The fragment separator FRS at GSI, Darmstadt provided the He and Li beams of near 0.7 GeV/u energy. The hydrogen-filled ionization chamber IKAR was used for the proton target and detector for recoil protons. Accurate data on absolute differential cross sections for proton elastic scattering at near-forward angles have been procured. Analysis of the cross section data with the aid of Glauber multiple scattering theory has allowed the nuclear matter radii of the He and Li isotopes to be determined, and the corresponding radial matter distributions to be deduced.

Details about experimental method and data analysis are given. The more recently measured elastic-scattering cross sections for the ^6,8,9,11Li isotopes are presented, and the nuclear matter radii and radial matter distributions deduced from the data at the present stage of the analysis are discussed.

The role of the entrance channel in fusion-fission reactions was studied by the theoretical analysis of the experimental evaporation residue excitation functions for reactions leading to the same compound nucleus. The evaporation residues cross sections for xn-channels were calculated in the frame of the combined dinuclear system concept (DNS) and advanced statistical model (ASM). The revealed differences between experimental data on the evaporation residues in the ⁴⁰Ar+¹⁷⁶Hf, ⁸⁶Kr + ¹³⁰Xe and ¹²⁴Sn + ⁹²Zr reactions leading to the ²¹⁶Th* compound nucleus (CN) as well as that between the ⁴⁸Ca + ¹⁷⁴Yb and ⁸⁶Kr + ¹³⁶Xe reactions leading to the ²²²Th* CN are explained by the different spin distributions of compound nuclei which are formed. It is shown that the intrinsic fusion barrier and size of potential well are different for every entrance channel.

It is shown that the known methods of the nuclear chronometry of the astrophysical processes have to be revised and corrected, taking into account distinctions between lifetimes of the ground and excited states for radioactive nuclei and also the multiple processes of γ-emissions from excited states with consequent γ-absorptions by ground in large masses of radioactive matter. In the result of this, (1) the corrected "nuclear clocks" indicate to smaller values of the durations of real decay processes, (2) the usual (non-corrected) "nuclear clocks" indicate to the upper limits of the durations of real decay processes.

The neutron separation energies (S_n) and the interaction cross-sections (σ₁) for the neutron-rich p-sd and sd shell region have been surveyed in order to search for a new magic number. Very recently, both measurements have reached up to the neutron drip-line, or close to the drip-line, for nuclei of Z • 8. The neutron-number (N) dependence of S_n shows clear breaks at N=16 near to the neutron drip-line, which shows the creation of a new magic number. A neutron number dependence of σ₁ shows a large increase of σ₁ for N=15, which supports the new magic number. The origin and influence of the new magic number are also discussed.

We propose a Constraint Molecular Dynamics model for Fermionic system. In this approach the equations of the nuclear many-body problem are solved by imposing that the one-body occupation number , evaluated for each particle, can assume only values less or equal to 1. Some comparison to data is given.

No abstract received.

Heavy ion collisions at intermediate energies offer the possibility to investigate the role of the isospin degree of freedom in determining the evolution of the reaction mechanism in an energy domain dominated by the competition between one body and two body nuclear dynamics. The REVERSE experiment has been carried on the period September 1999 – May 2000, at the Laboratory Nazionali del Sud in Catania, with the forward part of the 4π multidetector CHIMERA. This part of the device consists 688 Si-CsI (Tl) telescopes arranged in nine ring and has been used to study the inverse reactions ^112,124Sn+^58,64Ni, Al, at E_beam 35 MeV/A. Much care was devoted in calibrating the detectors in energy, charge and mass for the proper identification of light heavy nuclei and charged particles was obtained. The first physical results are presented.

The collisional relaxation times of collective vibrations are studied using both the transport approach and doorway state mechanism with hierarchy of particle-hole configurations in heated nuclei. It is shown that 1) the relaxation times of the kinetic method are rather slowly dependent on multipolarity of the Fermi surface distortion and mode of the collective motion; 2) variations of the in-medium two-body cross-sections with energy lead to non-quadratic dependence of the collisional relaxation time both on temperature and on collective motion frequency.

A series of experiments on the fission of superheavy nuclei formed in the reactions with ⁴⁸Ca ions, namely, the ⁴⁸Ca+²⁰⁸Pb, ⁴⁸Ca+²³²Th, ⁴⁸Ca+²³⁸U, ⁴⁸Ca+²⁴⁴Pu, ⁴⁸Ca+²⁴⁸Cm reactions, was carried out during the past two years at the Flerov Laboratory of Nuclear Reactions (JINR, Dubna). Experimental data were obtained on the mass and energy distributions of fission fragments of compound nuclei 102-116 in an excitation energy range of 13-44 MeV. The capture cross section σ_cap and fusion-fission cross section σ_FF were also estimated for these nuclei. As a result of the experiments it was found that the mass distribution of fission fragments for compound nuclei ²⁸⁶112, ²⁹²114, ²⁹⁶116 and ³⁰⁶122 is asymmetric. Its nature, in contrast to the asymmetric fission of actinides, is determined by the shell structure of the light fragment with the average mass 132-134. It was established that the TKE for fission and that for quasi-fission of superheavy compound nuclei are significantly different. The analysis of the σ_FF data and the σ_EV data [1] obtained in the study of the same elements testifies to the fact that at excitation energies E*~30-35 MeV the ratio σ_FF/σ_EV is changing insignificantly up to the nucleus Z=116. This fact allows one to hope for a successful synthesis of even heavier nuclei in asymmetric reactions.

The dynamics and thermodynamics of phase transition in nuclei are studied through experimental results on multifragmentation of systems with masses around 200 nucleons. Nuclear multifragmentation is indeed the phenomenon connected to the liquid-gas phase transition of nuclei. Negative heat capacities and spinodal decomposition are observed in a limited range of available energy, which sign the penetration of the systems in the coexistence zone of the phase diagram and thus a first order phase transition.

The fusion barriers experimentally investigated as well as the α and fission exit channels for superheavy elements have been determined within a Generalized Liquid Drop Model including the proximity effects, the asymmetry, an accurate nuclear radius and an adjustment to reproduce the experimental Q value. Double-hump fusion barriers appear in cold fusion reactions and, then, possible fast-fission events in the external well while warm fusion reactions lead to one peak potential barriers and to excited nuclei. The moment of emission of the excess neutrons or even an α particle is crucial to decide between complete fusion and fast fission.

The excitation functions for the evaporation residues (ER) produced in the complete fusion reactions induced by ⁸⁶Kr leading to the ¹⁹⁰Hg*, ²⁰⁹Fr*, ²¹⁶Ra*, ²¹⁶Th* and ²²²Th* compound nuclei (CN) have been analyzed in the framework of the HIVAP-code with the potential barrier passing and standard statistical model approximations and using similar data obtained in asymmetric combinations leading to the same CN. The excitation functions for ER obtained in the vicinity of the nominal fusion barrier for nearly symmetric projectile-target combinations show significant suppression of the production cross section for ER in comparison with those which can be predicted by the model. An attempt has been made to find correlations between the extracted values of the fusion probability and the values of the additional barrier, corresponding to the minima of the driving potential.

One of the most remarkable results of collision theory is the Optical Theorem, an extension to charged particles has been often used in nuclear physics to extract the reaction cross section. In the present work the Optical Theorem is used to obtain the fusion cross section for charged particles at energies below the Coulomb barrier. In fact by using experimental evidences and the Optical Theorem it is possible to obtain the fusion cross section in terms of Rutherford cross section and experimental values of differential elastic cross section.

Fission dynamics is investigated by solving the Langevin equation in a multi-dimensional deformation space. The influence of a neck degree of freedom, mass asymmetry and non-axiallity on fission times, and consequently, on prefission particle mutiplicities, is discussed. Differences of fission dynamics at low and high excitation energy, as well as deformation dependence of light particle emission width in Weisskopf and Thomas-Fermi models are pointed out.

Transfer induced fission probabilities P_f have been measured in the collisions of 340 MeV ²⁸Si on ²³²Th target as a function of the detected projectile-like fragment (PLF) charge. The measured P_f shows an increase with the net charge transfer ΔZ, in the range ΔZ =0-4. For larger ΔZ values (ΔZ =5-10), the fission probability exhibits first a saturation in the range of values P_f =0.4-0.6 and than a drop. Coincidences between PLF and light charge particles reveal that the charged particle emission is strongly damped when the fission fragments is required. An important component in the charged particle emission is localized in the direction of the recoiling target-like fragment (TLF); which is, in some cases, directly detected. Therefore results indicate a significant survival against fission of the populated TLF fragments.

A hybrid model combining deterministic dynamics with evaporation of light particles and/or dissipative fission is discussed. The model is applied in analysis of neutron multiplicities measured in fusion-fission and fast fission reactions in collisions of heavy nuclear systems. Results of simulations are compared with the correlation between the prescission and postscission multiplicities deduced with the backtracing method by the DéMoN Collaboration for a heavy composite system Z=110.

A few problems connected with the structure and properties of superheavy nuclei are considered. These are the problems of experimental confirmation of deformed shapes of nuclei situated around the nucleus ²⁷⁰Hs and the localization, in nuclear chart, of spherical superheavy nuclei with the largest (negative) shell correction to energy. Question of existence of superheavy nuclei in nature is also shortly discussed.

The reduced transition probabilities of and have been measured at GANIL by Coulomb excitation at intermediate energy in a ²⁰⁸Pb target. A remarkable change in the evolution of the B(E2) is seen while crossing the N=40 closed shell in Ni and Zn isotopic chains.

The dynamics of the fusion-fission process is being investigated over a wide range of mass, energy and angular momentum by the DEMON-CORSET collaboration. Results on the superheavy system Z=110 produced by different entrance channels at different excitation energies are presented. A new analysing procedure, the backtracing, gives access to the neutron multiplicity distributions as well as to the correlation between the pre- and post-scission emission, allowing for the first time to separate fusion-fission from fast fission.

The matter and charge distributions of lithium and beryllium isotopes were calculated in terms of interacting microscopic clusters: the valence- (one, two, three particles) and the intrinsic vacuum-clusters (collective-excitations of reference vacuum). Root-mean-square matter and charge radii have been extracted and are in good agreement with experimental results.

Peripheral transfer reactions can be used to determine asymptotic normalization coefficients (ANC). These coefficients, which provide the normalization of the tail of the overlap function, determine S factors for direct capture reactions at astro-physical energies. A variety of proton transfer reactions have been used to measure ANC's. As tests of the technique, ANC's for ¹⁰B ↔ ⁹Be + p and ¹⁷F ↔ ¹⁶O + p have been measured and their values were used to predict the S factors for ⁹Be(p,γ)¹⁰B and ¹⁶O(p,γ)¹⁷F. In both cases the predictions are in excellent agreement with measured S factors. Following the same technique, the ¹⁰B(⁷Be,⁸B)⁹Be and ¹⁴N(⁷Be,⁸B)¹³C reactions have been used to measure the ANC appropriate for determining ⁷Be(p,γ)⁸B. The results from the two transfer reactions provide an indirect determination of S₁₇(0). Recent measurements have been completed on the ¹⁴N(¹¹C,¹²N)¹³C reaction which will allow us to define the astrophysical S factor for the ¹¹C(p,γ)¹²N reaction.

The preparation of radioactive ¹⁰Be, ³⁷Ar and ³⁹Ar samples is discussed. Investigation of the ¹⁰Be(n_th,γ)¹¹Be,³⁷Ar(n_th,α)³⁴S,³⁷Ar(n_th,p)³⁷Cl and ³⁹Ar(n_th,α)³⁶S reactions is reported, and resonances in the ³⁷Ar(n,α)³⁴S reaction have been observed and analysed.

Excitation functions for fusion and/or capture reactions have been analysed in a phenomenological model assuming the Gaussian distribution of fusion barriers. Preliminary systematics of the barrier-distribution parameters show the role of nuclear structure effects, which we propose to account for by relating values of the dispersion parameter with fusion energy thresholds calculated assuming the fusion adiabatic potential.

We describe a large-acceptance (50 msr) high-resolution magnetic spectrometer "MAGNEX", which has been designed primarily for the radioactive beam facility EXCYT at INFN-LNS Catania. The configuration is a vertically-focusing quadrupole followed by a 55° bend angle dipole. The aberrations are corrected partly by shaping the entrance and exit effective field boundaries and partly by software compensation. Surface coils within the dipole pole-gap are used to compensate for the kinematic effect.

The study of ⁶He and ⁸He elastic scattering on a helium target and 2-neutron transfer reactions on protons are reported. The elastic scattering data were discussed in terms of presence of the backward angle enhancement caused by structural effects. The transfer reactions appeared to be an important source of information on neutron correlations in these nuclei.

A state of ⁴H with E_res=3.22± 0.15 MeV and Γ_obs=3.33 ± 0.25 MeV is obtained in t+d reaction. A valuable part of proton spectra observed in t+t reaction from ptn coincidence events is due to ⁵H. The ⁵H spectrum shows up a narrow maximum at about 2.5 MeV above the tnn decay threshold followed by a wide structure situated at 4-7 MeV.

No abstract received.

The crystal blocking technique has been used to measure the fission decay times in the ^natPt + ²⁸Si(140-170 MeV), ²³²Th + p(6-8 MeV), ²³²Th + ³He(20–24 MeV) and ²³²Th + α(20-31 MeV) reactions. The experimental data are analyzed in the frames of the statistical theory of nuclear reactions with allowance for the lifetimes of the excited states of the first and second potential wells of the double-humped fission barrier and taking into account the phenomenon of shell effect damping with increase of nuclear temperature.

No abstract received.

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