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We searched for a long-living component in the collision of 238U+238U between 6.09 A and 7.35 A MeV. The experiment was performed at GANIL using the spectrometer VAMOS, tuned for observing reactions with kinematics similar to quasi-fission events. Theoretical calculations indicate that reactions with strong energy dissipation and a large number of transferred nucleons are correlated to a time delay in the decay of the giant system. We detected events of such type in the focal plane of VAMOS. These events present an excitation function increasing with bombarding energy. [ABSTRACT FROM AUTHOR]

In the formation and evolution of compact stars, nuclear matter explores high thermal excursions and is the site of intense neutrino emission. Neutrino transport as well as structural properties of this matter depend on the presence of inhomogeneous phases (named “pasta” phases), which are the result of Coulomb frustration of the Liquid-Gas phase transition. We take into account charge fluctuations by employing a frustrated lattice-gas model to which we impose a neutrality constraint by the addition of an homogeneous background of charge, representing delocalised electrons. Within this schematic model we highlight a generaic feature of the phase-transition phenomenology: the temperature interval where pasta phases are formed is enhanced by Coulomb-frustration effects. This result is at variance with the behaviour of frustrated ferromagnetic systems as well as hot nuclei and mean-field approaches. Moreover, the region of phase coexistence is not found to end upon a critical point, indicating that no critical opalescence can occur in compact-star matter. [Copyright &y& Elsevier]

We have studied an effect of neutron and triton transfer reactions on the p +^6He elasticscatteringat25 MeV bymeansofcoupled - reaction - channelcalculations. Itisfoundthatwhenthetransferreactionsareexplicitlyincludedinthecalculationstheimaginarypartoftheinput$ p + $6He optical model potential has to be reduced by 52 percent while its real part enhanced by 15 percent in order to fit the elastic-scattering data. The effect of transfer channels on the real part of this potential is somewhat weaker than that of 6He breakup reported previously. However, for the imaginary part, the effect of transfer channels is dominant. It is concluded that while the breakup contribution to proton elastic scattering mainly affects the real part of the bare potential, the contribution of transfer channels affects mainly its imaginary part. [ABSTRACT FROM AUTHOR]

Energy integrated reaction cross-section measurements of around sixty neutron-rich nuclei covering the region of closed shells N = 20 and N = 28 were performed at intermediate energy (30-65 A . MeV) using direct method. In this experiment, silicon detectors were used as active targets. The reduced strong absorption radii, r02, for 19 new nuclei (27F, 27,30Ne, 33Na, 28, 34-35Mg, 36-38Al, 38-40Si, 41-42P, 42-44S and 45Cl) are deduced for the first time. An additional 60 radii, also measured in this experiment, are compared to results from literature. A new quadratic parametrization is proposed for the nuclear radius as a function of the isospin in the region of closed shells N = 8 and N = 28. According to this parametrization, the skin effect is well reproduced and anomalous behaviour on the radii are observed in 23N, 29Ne, 33Na, 35Mg, 44S, 45Cl and 45Ar nuclei. [ABSTRACT FROM AUTHOR]

Reactions induced on protons at low incident energy (3.5 MeV/n) were measured with a 8He beam accelerated by Spiral at Ganil. The particles were detected in the active target Maya, filled with C4H10 gas. The beam was stopped in the detector, so energies from incident beam energy down to detector threshold were covered. Proton elastic scattering, one neutron pick-up ( p, d) and ( p, t) reactions were observed. In the ( p, d) reaction very high cross-sections of the order of 1barn were observed, that could be reproduced using a direct reaction formalism. This is the first time that this strong increase of transfer reaction cross-sections at very low energy predicted for loosely bound systems was observed. Spectroscopic factors are in agreement with a simple shell model configuration. No evidence for a low lying excited state in 7He was found. [ABSTRACT FROM AUTHOR]

The fragmentation of 95 MeV/u 12C and 75 MeV/u 13C projectiles, interacting with natural targets of different elements (9Be, natCu and 197Au for 12C, and 9Be, natNi, and 181Ta for 13C) and of various thicknesses has been investigated at GANIL, using the doubly achromatic magnetic spectrometer LISE. The projectile-like fragments transmitted at 0° have been analysed using a silicon ΔE-E telescope and the ΔE-time-of-flight method. The results obtained with the thinnest targets are discussed in the scope of radioactive nuclear beam production. The fragment momentum distributions can be fitted by Gaussian peaks associated with exponential tails towards low momentum values. The experimental production yields are compared with the results of the simulation code LISE. It appears that this code reproduces satisfactorily the yields of nuclei close to the stability line, but strongly overestimates the production of very neutron-deficient nuclei. [ABSTRACT FROM AUTHOR]

The elastic scattering of strongly bound nuclei at energies of 10 to 70 MeV per nucleon shows the phenomenon of "rainbow scattering." A nuclear rainbow appears because of deflection to negative angles. This process involves a strong overlap of nuclear densities, with values of up to twice the saturation density of nuclear matter. The [sup 16]O + [sup 16]O system is studied with a high precision over a wide energy range from 7 to 70 MeV per nucleon in several laboratories. Primary Airy maxima and higher order Airy structures are observed. At all energies, excellent fits are obtained with deep potentials as deduced from the double-folding model involving a nucleon-nucleon interaction weakly dependent on the density. It is shown that Pauli blocking expected at low energies is strongly reduced if the local momenta are calculated self-consistently. Systematics confirms a refractive origin of large-angle scattering, at low energies inclusive. Thus, nuclear-rainbow scattering yields unique information about the properties of cold nuclear matter at higher densities. [ABSTRACT FROM AUTHOR]

A secondary radioactive ion beam produced from fragmentation of a primary beam in a target has a large emittance and momentum spread after a fragment separator. At low production rates of 1–106 ion/s the parameters of each particle can be measured individually with a rather high accuracy. We propose to use an “individual trajectory correction” in an appropriate transfer channel, and “individual injection” in a storage ring and a fast stacking procedure for the injected beam at small emittance and momentum spread. With such a scheme it is possible to obtain a storage rate of 5×102–103 ions/s at an ion flux of 103–104 ions/s. This represents 5–6 orders of magnitude increase of the injection efficiency as compared to standard multiturn injection with a continuous beam at low intensity. [Copyright &y& Elsevier]

Abstract: The break-up of 11Be was studied at 41 AMeV using a secondary beam of 11Be from the GANIL facility on a 48Ti target by measuring correlations between the 10Be core, the emitted neutrons and gamma rays. The nuclear break-up leading to the emission of a neutron at large angle in the laboratory frame is identified with the “towing mode” through its characteristic n-fragment correlation. The experimental spectra are compared with a model where the time dependent Schrödinger equation (TDSE) is solved for the neutron initially in the 11Be. A good agreement is found between experiment and theory for the shapes of neutron experimental energies and angular distributions. The spectroscopic factor of the 2s orbital is tentatively extracted to be . The neutron emission from the 1p and 1d orbitals is also studied. [Copyright &y& Elsevier]

Abstract: Mass measurements of very neutron-rich nuclei near the and 28 shell closures are presented. Seven masses have been determined for the first time and the precision of 36 masses has been significantly improved. These results are used to investigate the evolution of the odd–even staggering of binding energies with neutron number. Special attention is paid to the evolution of the shell closure as the neutron dripline is approached. Changes in shell structure are observed around for the P and S isotopes but not for Si. This may be interpreted as a persistence of the shell closure at or as the result of a very sudden onset in deformation at 42Si. [Copyright &y& Elsevier]

The structure of the light exotic nucleus 8He was investigated using direct reactions of the 8He SPIRAL beam on a proton-rich target. The (p,p'') scattering to the state, the (p,d)7He and (p,t)6He transfer reactions, were measured at the energy . The light charged particles (p,d,t) were detected in the MUST Si-strip telescope array. The excitation spectrum of 8He was extracted from the (p,p'') reaction. Above the known excited state at 3.6 MeV, a second resonance was found around 5.4 MeV. The cross sections were analyzed within the coupled-reaction channels framework, using microscopic potentials. It is inferred that the 8He ground state has a more complex neutron-skin structure than suggested by previous models assuming a pure configuration. [Copyright &y& Elsevier]

Abstract: The weakly-bound 8He nucleus exhibits a neutron halo or thick neutron skin and is generally considered to have an structure in its ground state, with the four valence neutrons each occupying states outside the α core. The 8He()6He reaction is a sensitive probe of the ground state structure of 8He, and we present a consistent analysis of new and existing data for this reaction at incident energies of 15.7 and , respectively. Our results are incompatible with the usual assumption of a pure structure and suggest that other configurations such as may be present with significant probability in the ground state wave function of 8He. [Copyright &y& Elsevier]

Abstract: The spectroscopy of 27Ne has been investigated through the one-neutron transfer reaction 26Ne()27Ne in inverse kinematics at 9.7 MeV/nucleon. The results strongly support the existence of a low-lying negative parity state in 27Ne, which is a signature of a reduced sd–fp shell gap in the neutron-rich region, at variance with stable nuclei. [Copyright &y& Elsevier]

Abstract: The and reactions were measured in inverse kinematics at and analyzed within the coupled reaction channels framework, the cross section being particularly large. We find that coupling to pickup has a profound effect on the elastic scattering, and that these strong coupling effects should be included in analyses of proton elastic and inelastic scattering. Through its modification of the elastic scattering wave functions this coupling will strongly affect the extraction of spectroscopic information such as the relationship between neutron and proton nuclear deformations, with important consequences for our understanding of the structure of exotic nuclei. [Copyright &y& Elsevier]