572 research outputs found
Deformation mechanisms and damage of oxide dispersion strengthened steels at high temperature
International audienceA ferritic oxide dispersion strengthened steel is under study for fuel cladding applications in future nuclear systems. Tensile tests and creep tests are carried out at various temperatures to determine its mechanical properties along the extrusion direction. For these two types of loading, the material exhibits a high mechanical resistance. Its ductility appears to be strongly influenced by the strain rate and the temperature. Deformation mechanisms linked to diffusion phenomena are suspected and intergranular damage is observed on fractured specimens
Energy and angular momentum sharing in dissipative collisions
Primary and secondary masses of heavy reaction products have been deduced
from kinematics and E-ToF measurements, respectively, for the direct and
reverse collisions of 93Nb and 116Sn at 25 AMeV. Light charged particles have
also been measured in coincidence with the heavy fragments.
Direct experimental evidence of the correlation of energy-sharing with net
mass transfer has been found using the information from both the heavy
fragments and the light charged particles.
The ratio of Hydrogen and Helium multiplicities points to a further
correlation of angular momentum sharing with net mass transfer.Comment: 21 pages, 20 figures. Submitted to European Physics Journal
Multifragmentation threshold in ^{93}Nb+{nat}Mg collisions at 30 MeV/nucleon
We analyzed the on reaction at 30 MeV/nucleon in the aim
of disentangling binary sequential decay and multifragmentation decay close to
the energy threshold, i.e. MeV/nucleon. Using the backtracing
technique applied to the statistical models GEMINI and SMM we reconstruct
simulated charge, mass and excitation energy distributions and compare them to
the experimental ones. We show that data are better described by SMM than by
GEMINI in agreement with the fact that multifragmentation is responsible for
fragment production at excitation energies around 3 MeV/nucleon.Comment: 16 pages, 12 figures, 5 tables Soumis \`a Nuclear Physics
Limitation of energy deposition in classical N body dynamics
Energy transfers in collisions between classical clusters are studied with
Classical N Body Dynamics calculations for different entrance channels. It is
shown that the energy per particle transferred to thermalised classical
clusters does not exceed the energy of the least bound particle in the cluster
in its ``ground state''. This limitation is observed during the whole time of
the collision, except for the heaviest system.Comment: 13 pages, 15 figures, 1 tabl
Measuring the Temperature of Hot Nuclear Fragments
A new thermometer based on fragment momentum fluctuations is presented. This
thermometer exhibited residual contamination from the collective motion of the
fragments along the beam axis. For this reason, the transverse direction has
been explored. Additionally, a mass dependence was observed for this
thermometer. This mass dependence may be the result of the Fermi momentum of
nucleons or the different properties of the fragments (binding energy, spin
etc..) which might be more sensitive to different densities and temperatures of
the exploding fragments. We expect some of these aspects to be smaller for
protons (and/or neutrons); consequently, the proton transverse momentum
fluctuations were used to investigate the temperature dependence of the source
Monitoring Of 14 Mev Neutrons
Long-lived fission products and minor actinides produced in nuclear power plants are the most radiotoxic nuclear wastes. They can be transmuted into stable nuclei or into nuclei with shorter lifetime thanks to the so-called Accelerator Driven Systems (ADS), consisting of the coupling of an intense high energy proton beam, a spallation target and a sub-critical reactor core. For safety reasons, an on-line and robust measurement of the reactivity during loading and power operation is mandatory. The investigation of the relationship between the current of the accelerator and the power level (or neutron flux) of the reactor appears to be powerful, any change in reactivity being accessible through the measurement of the current and the flux. Such a relationship will be studied in an experiment to be performed at the YALINA facility (JIPNR Sosny - Belarus) in the framework of the EUROTRANS IP (6 FP). At this installation, 14 MeV neutrons are produced in T(d,n)He reactions by a deuteron beam impinging on a TiT target. Due to the tritium consumption over time, the intensity of the deuteron beam cannot be used for the monitoring of the neutron beam. The source neutron yield itself has to be accessed. This contribution describes the performance of a three-element silicon telescope dedicate
Statistical Multifragmentation of Non-Spherical Expanding Sources in Central Heavy-Ion Collisions
We study the anisotropy effects measured with INDRA at GSI in central
collisions of Xe+Sn at 50 A.MeV and Au+Au at 60, 80, 100 A.MeV incident energy.
The microcanonical multifragmentation model with non-spherical sources is used
to simulate an incomplete shape relaxation of the multifragmenting system. This
model is employed to interpret observed anisotropic distributions in the
fragment size and mean kinetic energy. The data can be well reproduced if an
expanding prolate source aligned along the beam direction is assumed. An either
non-Hubblean or non-isotropic radial expansion is required to describe the
fragment kinetic energies and their anisotropy. The qualitative similarity of
the results for the studied reactions suggests that the concept of a
longitudinally elongated freeze-out configuration is generally applicable for
central collisions of heavy systems. The deformation decreases slightly with
increasing beam energy.Comment: 35 pages, 19 figures, submitted to Nuclear Physics
Dynamical effects in multifragmentation at intermediate energies
The fragmentation of the quasi-projectile is studied with the INDRA
multidetector for different colliding systems and incident energies in the
Fermi energy range. Different experimental observations show that a large part
of the fragmentation is not compatible with the statistical fragmentation of a
fully equilibrated nucleus. The study of internal correlations is a powerful
tool, especially to evidence entrance channel effects. These effects have to be
included in the theoretical descriptions of nuclear multifragmentation.Comment: 13 pages, 26 figures, submitted to Physical Review
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