144 research outputs found
Numerical modelling and in-situ experiment for self-sealing of the induced fracture network of drift into the Callovo-Oxfordian claystone during a hydration process
The excavation damage zone surrounding an underground tunnel/gallery, and in particular its evolution, is being studied for the performance assessment of a radioactive waste underground repository. This paper focuses on numerical analysis of the self-sealing of the damaged zone based on an in-situ CDZ experiment for exploring the self-sealing of excavation damage zone during a hydration process. A plastic damage model is employed to describe the mechanical behaviour of Callovo-Oxfordian claystone (COx), and an added deformation model coupled with the standard Biot's model to simulate the significant deformation of COx claystone during the change of water content. Crack estimation and permeability evaluation of unsaturated fractured COx claystone are carried out through a post-processing method based on the fracture energy regularization and the cubic law, respectively. The validation of the proposed model is performed by numerical simulation of: (1) COx claystone swelling and triaxial compression tests, (2) self-sealing of fractured COx claystone samples during hydration process, (3) self-sealing of the damaged zone during a hydration process. Comparisons between the numerical and experimental results demonstrate the reliability of the proposed model to accurately describe the self-sealing of the fractured COx claystone, and the global water permeability reduction in hydration illustrates the accomplishment of the self-sealing of damaged zone
Signals of Bose Einstein condensation and Fermi quenching in the decay of hot nuclear systems
We report experimental signals of Bose-Einstein condensation in the decay of
hot Ca projectile-like sources produced in mid-peripheral collisions at
sub-Fermi energies. The experimental setup, constituted by the coupling of the
INDRA 4 detector array to the forward angle VAMOS magnetic spectrometer,
allowed us to reconstruct the mass, charge and excitation energy of the
decaying hot projectile-like sources. Furthermore, by means of quantum
fluctuation analysis techniques, temperatures and mean volumes per particle "as
seen by" bosons and fermions separately are correlated to the excitation energy
of the reconstructed system. The obtained results are consistent with the
production of dilute mixed (bosons/fermions) systems, where bosons experience a
smaller volume as compared to the surrounding fermionic gas. Our findings
recall similar phenomena observed in the study of boson condensates in atomic
traps.Comment: Submitted to Phys. Rev. Lett. (december 2014
Production of -particle condensate states in heavy-ion collisions
The fragmentation of quasi-projectiles from the nuclear reaction +
at 25 MeV/nucleon was used to produce excited states candidates to
-particle condensation. The experiment was performed at LNS-Catania
using the CHIMERA multidetector. Accepting the emission simultaneity and
equality among the -particle kinetic energies as experimental criteria
for deciding in favor of the condensate nature of an excited state, we analyze
the and states of C and the state of O. A
sub-class of events corresponding to the direct 3- decay of the Hoyle
state is isolated.Comment: contribution to the 2nd Workshop on "State of the Art in Nuclear
Cluster Physics" (SOTANCP2), Universite Libre de Bruxelles (Belgium), May
25-28, 2010, to be published in the International Journal of Modern Physics
Influence of Neutron Enrichment on Disintegration Modes of Compound Nuclei
Cross sections, kinetic energy and angular distributions of fragments with
charge 6Z28 emitted in 78,82Kr+40C at 5.5 MeV/A reactions were
measured at the GANIL facility using the INDRA apparatus. This experiment aims
to investigate the influence of the neutron enrichment on the decay mechanism
of excited nuclei. Data are discussed in comparison with predictions of
transition state and Hauser-Feshbach models.Comment: 8 pages, 1 figure, paper presented at the First Workshop on "State of
the Art in Nuclear Cluster Physics" 13-16 May, 2008, at Strasbourg, France
(SOTANCP2008) and accepted for publication at International Journal of Modern
Physics E (Special Issue), Proceedings of SOTANCP2008 (to be published
Multifragmentation of a very heavy nuclear system (II): bulk properties and spinodal decomposition
The properties of fragments and light charged particles emitted in
multifragmentation of single sources formed in central 36AMeV Gd+U collisions
are reviewed. Most of the products are isotropically distributed in the
reaction c.m. Fragment kinetic energies reveal the onset of radial collective
energy. A bulk effect is experimentally evidenced from the similarity of the
charge distribution with that from the lighter 32AMeV Xe+Sn system. Spinodal
decomposition of finite nuclear matter exhibits the same property in simulated
central collisions for the two systems, and appears therefore as a possible
mechanism at the origin of multifragmentation in this incident energy domain.Comment: 28 pages including 14 figures; submitted to Nucl. Phys.
Projected Quasi-particle Perturbation theory
The BCS and/or HFB theories are extended by treating the effect of four
quasi-particle states perturbatively. The approach is tested on the pairing
hamiltonian, showing that it combines the advantage of standard perturbation
theory valid at low pairing strength and of non-perturbative approaches
breaking particle number valid at higher pairing strength. Including the
restoration of particle number, further improves the description of pairing
correlation. In the presented test, the agreement between the exact solution
and the combined perturbative + projection is almost perfect. The proposed
method scales friendly when the number of particles increases and provides a
simple alternative to other more complicated approaches
Alpha-particle condensation in excited 12C
The fragmentation of quasi-projectiles from the nuclear reaction
+ at 25 MeV/nucleon was used to produce excited states
candidates to -particle condensation. The methodology relies on high
granularity 4 detection coupled to correlation function techniques. Under
the assumption that the equality among the kinetic energies of the emitted
-particles and the emission simultaneity constitutes a reliable
fingerprint of condensation, we identify several tens of events
corresponding to the deexcitation of the Hoyle state of C which fulfill
the condition.Comment: 5 pages, 3 figure
Measurements of sideward flow around the balance energy
Sideward flow values have been determined with the INDRA multidetector for
Ar+Ni, Ni+Ni and Xe+Sn systems studied at GANIL in the 30 to 100 A.MeV incident
energy range. The balance energies found for Ar+Ni and Ni+Ni systems are in
agreement with previous experimental results and theoretical calculations.
Negative sideward flow values have been measured. The possible origins of such
negative values are discussed. They could result from a more important
contribution of evaporated particles with respect to the contribution of
promptly emitted particles at mid-rapidity. But effects induced by the methods
used to reconstruct the reaction plane cannot be totally excluded. Complete
tests of these methods are presented and the origins of the
``auto-correlation'' effect have been traced back. For heavy fragments, the
observed negative flow values seem to be mainly due to the reaction plane
reconstruction methods. For light charged particles, these negative values
could result from the dynamics of the collisions and from the reaction plane
reconstruction methods as well. These effects have to be taken into account
when comparisons with theoretical calculations are done.Comment: 27 pages, 15 figure
Study of intermediate velocity products in the Ar+Ni collisions between 52 and 95 A.MeV
Intermediate velocity products in Ar+Ni collisions from 52 to 95 A.MeV are
studied in an experiment performed at the GANIL facility with the 4
multidetector INDRA. It is shown that these emissions cannot be explained by
statistical decays of the quasi-projectile and the quasi-target in complete
equilibrium. Three methods are used to isolate and characterize intermediate
velocity products. The total mass of these products increases with the violence
of the collision and reaches a large fraction of the system mass in mid-central
collisions. This mass is found independent of the incident energy, but strongly
dependent on the geometry of the collision. Finally it is shown that the
kinematical characteristics of intermediate velocity products are weakly
dependent on the experimental impact parameter, but strongly dependent on the
incident energy. The observed trends are consistent with a
participant-spectator like scenario or with neck emissions and/or break-up.Comment: 37 pages, 13 figure
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