327 research outputs found
Double Rosensweig instability in a ferrofluid sandwich structure
We consider a horizontal ferrofluid layer sandwiched between two layers of
immiscible non-magnetic fluids. In a sufficiently strong vertical magnetic
field the flat interfaces between magnetic and non-magnetic fluids become
unstable to the formation of peaks. We theoretically investigate the interplay
between these two instabilities for different combinations of the parameters of
the fluids and analyze the evolving interfacial patterns. We also estimate the
critical magnetic field strength at which thin layers disintegrate into an
ordered array of individual drops
Super-lattice, rhombus, square, and hexagonal standing waves in magnetically driven ferrofluid surface
Standing wave patterns that arise on the surface of ferrofluids by (single
frequency) parametric forcing with an ac magnetic field are investigated
experimentally. Depending on the frequency and amplitude of the forcing, the
system exhibits various patterns including a superlattice and subharmonic
rhombuses as well as conventional harmonic hexagons and subharmonic squares.
The superlattice arises in a bicritical situation where harmonic and
subharmonic modes collide. The rhombic pattern arises due to the non-monotonic
dispersion relation of a ferrofluid
Multifragmentation process for different mass asymmetry in the entrance channel around the Fermi energy
The influence of the entrance channel asymmetry upon the fragmentation
process is addressed by studying heavy-ion induced reactions around the Fermi
energy. The data have been recorded with the INDRA 4pi array. An event
selection method called the Principal Component Analysis is presented and
discussed. It is applied for the selection of central events and furthermore to
multifragmentation of single source events. The selected subsets of data are
compared to the Statistical Multifragmentation Model (SMM) to check the
equilibrium hypothesis and get the source characteristics. Experimental
comparisons show the evidence of a decoupling between thermal and compresional
(radial flow) degrees of freedom in such nuclear systems.Comment: 28 pages, 15 figures, article sumitted to Nuclear Physics
Response of CsI(Tl) scintillators over a large range in energy and atomic number of ions (Part I): recombination and delta -- electrons
A simple formalism describing the light response of CsI(Tl) to heavy ions,
which quantifies the luminescence and the quenching in terms of the competition
between radiative transitions following the carrier trapping at the Tl
activator sites and the electron-hole recombination, is proposed. The effect of
the delta rays on the scintillation efficiency is for the first time
quantitatively included in a fully consistent way. The light output expression
depends on four parameters determined by a procedure of global fit to
experimental data.Comment: 28 pages, 6 figures, submitted to Nucl. Inst. Meth.
Spallation Residues in the Reaction 56Fe + p at 0.3, 0.5, 0.75, 1.0 and 1.5 A GeV
The spallation residues produced in the bombardment of 56}Fe at 1.5, 1.0,
0.75, 0.5 and 0.3 A GeV on a liquid-hydrogen target have been measured using
the reverse kinematics technique and the Fragment Separator at GSI (Darmstadt).
This technique has permitted the full identification in charge and mass of all
isotopes produced with cross-sections larger than 10^{-2} mb down to Z=8. Their
individual production cross-sections and recoil velocities at the five energies
are presented. Production cross-sections are compared to previously existing
data and to empirical parametric formulas, often used in cosmic-ray
astrophysics. The experimental data are also extensively compared to different
combinations of intra-nuclear cascade and de-excitation models. It is shown
that the yields of the lightest isotopes cannot be accounted for by standard
evaporation models. The GEMINI model, which includes an asymmetric fission
decay mode, gives an overall good agreement with the data. These experimental
data can be directly used for the estimation of composition modifications and
damages in materials containing iron in spallation sources. They are also
useful for improving high precision cosmic-ray measurements.Comment: Submited to Phys. Rev. C (10/2006
Isospin dependent multifragmentation of relativistic projectiles
The N/Z dependence of projectile fragmentation at relativistic energies has
been studied with the ALADIN forward spectrometer at the GSI Schwerionen
Synchrotron (SIS). Stable and radioactive Sn and La beams with an incident
energy of 600 MeV per nucleon have been used in order to explore a wide range
of isotopic compositions. For the interpretation of the data, calculations with
the statistical multifragmentation model for a properly chosen ensemble of
excited sources were performed. The parameters of the ensemble, representing
the variety of excited spectator nuclei expected in a participant-spectator
scenario, are determined empirically by searching for an optimum reproduction
of the measured fragment-charge distributions and correlations. An overall very
good agreement is obtained. The possible modification of the liquid-drop
parameters of the fragment description in the hot freeze-out environment is
studied, and a significant reduction of the symmetry-term coefficient is found
necessary to reproduce the mean neutron-to-proton ratios /Z and the
isoscaling parameters of Z<=10 fragments. The calculations are, furthermore,
used to address open questions regarding the modification of the surface-term
coefficient at freeze-out, the N/Z dependence of the nuclear caloric curve, and
the isotopic evolution of the spectator system between its formation during the
initial cascade stage of the reaction and its subsequent breakup.Comment: 23 pages, 29 figures, published in Physical Review
Evidence for Spinodal Decomposition in Nuclear Multifragmentation
Multifragmentation of a ``fused system'' was observed for central collisions
between 32 MeV/nucleon 129Xe and natSn. Most of the resulting charged products
were well identified thanks to the high performances of the INDRA 4pi array.
Experimental higher-order charge correlations for fragments show a weak but non
ambiguous enhancement of events with nearly equal-sized fragments. Supported by
dynamical calculations in which spinodal decomposition is simulated, this
observed enhancement is interpreted as a ``fossil'' signal of spinodal
instabilities in finite nuclear systems.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Letter
Effect of the intermediate velocity emissions on the quasi-projectile properties for the Ar+Ni system at 95 A.MeV
The quasi-projectile (QP) properties are investigated in the Ar+Ni collisions
at 95 A.MeV taking into account the intermediate velocity emission. Indeed, in
this reaction, between 52 and 95 A.MeV bombarding energies, the number of
particles emitted in the intermediate velocity region is related to the overlap
volume between projectile and target. Mean transverse energies of these
particles are found particularly high. In this context, the mass of the QP
decreases linearly with the impact parameter from peripheral to central
collisions whereas its excitation energy increases up to 8 A.MeV. These results
are compared to previous analyses assuming a pure binary scenario
Isotopic Dependence of the Nuclear Caloric Curve
The A/Z dependence of projectile fragmentation at relativistic energies has
been studied with the ALADIN forward spectrometer at SIS. A stable beam of
124Sn and radioactive beams of 124La and 107Sn at 600 MeV per nucleon have been
used in order to explore a wide range of isotopic compositions. Chemical
freeze-out temperatures are found to be nearly invariant with respect to the
A/Z of the produced spectator sources, consistent with predictions for expanded
systems. Small Coulomb effects (\Delta T \approx 0.6 MeV) appear for residue
production near the onset of multifragmentation.Comment: 11 pages, 3 figures, accepted for publ. in Phys. Rev. Let
Tracing a phase transition with fluctuations of the largest fragment size: Statistical multifragmentation models and the ALADIN S254 data
A phase transition signature associated with cumulants of the largest
fragment size distribution has been identified in statistical
multifragmentation models and examined in analysis of the ALADIN S254 data on
fragmentation of neutron-poor and neutron-rich projectiles. Characteristics of
the transition point indicated by this signature are weakly dependent on the
A/Z ratio of the fragmenting spectator source. In particular, chemical
freeze-out temperatures are estimated within the range 5.9 to 6.5 MeV. The
experimental results are well reproduced by the SMM model.Comment: 7 pages, 3 figures, Proceedings of the International Workshop on
Multifragmentation and Related Topics (IWM2009), Catania, Italy, November
2009
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