Fusion reactions involving radioactive beams at GANIL

The ISOL type SPIRAL facility at GANIL has been commissioned recently and delivers radioactive beams (RIBs) for physics since a couple of years. Despite many difficulties arising from both the complexity to produce good beam quality and intensity as well as to setup the appropriate detection system, the first experiments with SPIRAL have demonstrated that nuclear dynamics studies (nuclear structure and low energy reaction mechanism) at the Coulomb barrier are possible with that kind of beams. RIBs like $^{76}$Kr and $^{6,8}$He have been used to produce exotic nuclei via fusion evaporation or to study reaction mechanisms at low energy. These two examples will be detailed in this talk

Quantum Calculation of Dipole Excitation in Fusion Reaction

The excitation of the giant dipole resonance by fusion is studied with N/Z asymmetry in the entrance channel. the TDHF solution exhibits a strong dipole vibration which can be associated with a giant vibration along the main axis of a fluctuating prolate shape. The consequences on the gamma-ray emission from hot compound nuclei are discussed

Quantum calculations of Coulomb reorientation for sub-barrier fusion

Classical mechanics and Time Dependent Hartree-Fock (TDHF) calculations of heavy ions collisions are performed to study the rotation of a deformed nucleus in the Coulomb field of its partner. This reorientation is shown to be independent on charges and relative energy of the partners. It only depends upon the deformations and inertias. TDHF calculations predict an increase by 30% of the induced rotation due to quantum effects while the nuclear contribution seems negligible. This reorientation modifies strongly the fusion cross-section around the barrier for light deformed nuclei on heavy collision partners. For such nuclei a hindrance of the sub-barrier fusion is predicted.Comment: accepted for publication in Physical Review Lette

Algorithms of numerical simulation of elastic waves propagating in dissipative environments

The simulation of propagating waves is of primary importance in many engineering applications, such as planning ultrasonic measurement procedures, monitoring of the structural integrity of pipelines by analyzing pressure pulses propagation, earthquake waves propagation and many other types of real-life applications. Traditionally, the computational methods of wave propagation analysis in geometrically complex structures and environments use the finite element or the finite difference approaches. However, inherent shortcomings arise due to huge dimensionalities of the models in cases when the length of the analyzed waves is much lesser than the linear dimensions of the structure. The limit situation is the infinite wave propagation environment in one or several directions, which actually is extremely difficult to simulate by traditional FEM because fictitious wave reflections form artificially introduced boundaries of the computational domain. The existing techniques within traditional FEM which enable to cope with the infinite domains are the non-reflecting boundary condition (suitable only for acoustic waves), scaled-boundary FEM techniques and perfectly matched layers. However, the latter approaches are approximate, and they also require significant computational resources, anyway. The semi-analytical approaches such as the SAFE method seem to be promising as they enable their users to avoid the discretization of the structures along the infinite direction. Even though the principles of SAFE have been well-known for several decades, the approach is still underdeveloped as perfectly as the traditional FEM – therefore, further research is still necessary. The guided waves in the waveguide (plate, bar, pipe, etc.) are described by their dispersion curves. The dispersion curves present the relationships of phase, group and energy velocities of the waves against the wave frequency. The SAFE method facilitates the calculation of dispersion curves for waveguides having uniform cross-section geometries along at least one direction. The finite element covers the discretization of the waveguide cross-section only. Along the wave propagation direction, the harmonic solutions in space and time are used. The expressions of such solutions use the exponential functions in the space of complex numbers. Similarly to the conventional FEM, the SAFEM enables to express forced time-dependent wave response analysis as a superposition of modal responses. While there are many researches addressing waveguides in vacuum, SAFE modeling of traveling waves in dissipative environments is still a challenging task. It is caused by the fact that the traditional SAFE analyses presume the amplitude decay of the traveling wave as negligible and, therefore, certain mathematical simplifications of the FE formulation are possible. In the case of higher damping, such simplifications would lead to considerable errors of the solution. In this research, the SAFE formulation is extended in order to treat the wave propagation problems in viscous environments. The energy dissipation model is presented via Rayleigh damping (i.e., energy dissipation caused by material damping) and via the leaky wave, where the waveguide immersed into the perfect fluid is considered

First observation of 55,56Zn

In an experiment at the SISSI/LISE3 facility of GANIL, the most proton-rich zinc isotopes 55,56Zn have been observed for the first time. The experiment was performed using a high-intensity 58Ni beam at 74.5 MeV/nucleon impinging on a nickel target. The identification of 55,56Zn opens the way to 54Zn, a good candidate for two-proton radioactivity according to theoretical predictions.Comment: 2 pages, 1 figure, accepted for publication in Eur. Phys. J.

Decay of proton-rich nuclei between 39Ti and 49Ni

Decay studies of very neutron-deficient nuclei ranging from 39Ti to 49Ni have been performed during a projectile fragmentation experiment at the GANIL/LISE3 separator. For all nuclei studied in this work, 39,40Ti, 42,43Cr, 46Mn, 45,46,47Fe and 49Ni, half-lives and decay spectra have been measured. In a few cases, gamma coincidence measurements helped to successfully identify the initial and final states of transitions. In these cases, partial decay scheme are proposed. For the most exotic isotopes, 39Ti, 42Cr, 45Fe and 49Ni, which are candidates for two-proton radioactivity from the ground state, no clear evidence of this process is seen in our spectra and we conclude rather on a delayed particle decay.Comment: 12 pages, 15 figures, submitted for publication in Eur. Phys. J.

Upregulation of Interleukin 8 by Oxygen-deprived Cells in Glioblastoma Suggests a Role in Leukocyte Activation, Chemotaxis, and Angiogenesis

Leukocyte infiltration and necrosis are two biological phenomena associated with the development of neovascularization during the malignant progression of human astrocytoma. Here, we demonstrate expression of interleukin (IL)-8, a cytokine with chemotactic and angiogenic properties, and of IL-8–binding receptors in astrocytoma. IL-8 expression is first observed in low grade astrocytoma in perivascular tumor areas expressing inflammatory cytokines. In glioblastoma, it further localizes to oxygen-deprived cells surrounding necrosis. Hypoxic/anoxic insults on glioblastoma cells in vitro using anaerobic chamber systems or within spheroids developing central necrosis induced an increase in IL-8 messenger RNA (mRNA) and protein expression. mRNA for IL-8–binding chemokine receptors CXCR1, CXCR2, and the Duffy antigen receptor for chemokines (DARC) were found in all astrocytoma grades by reverse transcription/PCR analysis. In situ hybridization and immunohistochemistry localized DARC expression on normal brain and tumor microvascular cells and CXCR1 and CXCR2 expression to infiltrating leukocytes. These results support a model where IL-8 expression is initiated early in astrocytoma development through induction by inflammatory stimuli and later in tumor progression increases due to reduced microenvironmental oxygen pressure. Augmented IL-8 would directly and/or indirectly promote angiogenesis by binding to DARC and by inducing leukocyte infiltration and activation by binding to CXCR1 and CXCR2

HST measures of Mass Accretion Rates in the Orion Nebula Cluster

The present observational understanding of the evolution of the mass accretion rates (Macc) in pre-main sequence stars is limited by the lack of accurate measurements of Macc over homogeneous and large statistical samples of young stars. Such observational effort is needed to properly constrain the theory of star formation and disk evolution. Based on HST/WFPC2 observations, we present a study of Macc for a sample of \sim 700 sources in the Orion Nebula Cluster, ranging from the Hydrogen-burning limit to M\ast \sim 2M\odot. We derive Macc from both the U-band excess and the H{\alpha} luminosity (LH{\alpha}), after determining empirically both the shape of the typical accretion spectrum across the Balmer jump and the relation between the accretion luminosity (Lacc) and LH{\alpha}, that is Lacc/L\odot = (1.31\pm0.03)\cdotLH{\alpha}/L\odot + (2.63\pm 0.13). Given our large statistical sample, we are able to accurately investigate relations between Macc and the parameters of the central star such as mass and age. We clearly find Macc to increase with stellar mass, and decrease over evolutionary time, but we also find strong evidence that the decay of Macc with stellar age occurs over longer timescales for more massive PMS stars. Our best fit relation between these parameters is given by: log(Macc/M\odot\cdotyr)=(-5.12 \pm 0.86) -(0.46 \pm 0.13) \cdot log(t/yr) -(5.75 \pm 1.47)\cdot log(M\ast/M\odot) + (1.17 \pm 0.23)\cdot log(t/yr) \cdot log(M\ast/M\odot). These results also suggest that the similarity solution model could be revised for sources with M\ast > 0.5M\odot. Finally, we do not find a clear trend indicating environmental effects on the accretion properties of the sources.Comment: 17 pages, 15 figures, accepted for publication in Ap