813 research outputs found
Comparison of fragment partitions production in peripheral and central collisions
Ensembles of single-source events, produced in peripheral and central
collisions and correponding respectively to quasi-projectile and quasi-fusion
sources, are analyzed. After selections on fragment kinematic properties,
excitation energies of the sources are derived using the calorimetric method
and the mean behaviour of fragments of the two ensembles are compared.
Differences observed in their partitions, especially the charge asymmetry, can
be related to collective energy deposited in the systems during the collisions.Comment: 7 pages, 2 figures, presented at the International Workshop on
Multifragmentation and Related Topics, Caen France, 4-7th november 2007
(IWM2007
Break-up fragments excitation and the freeze-out volume
We investigate, in microcanonical multifragmentation models, the influence of
the amount of energy dissipated in break-up fragments excitation on freeze-out
volume determination. Assuming a limiting temperature decreasing with nuclear
mass, we obtain for the Xe+Sn at 32 MeV/nucleon reaction [J. D. Frankland et
al., Nucl. Phys. A689, 905 (2001); A689, 940 (2001)] a freeze-out volume almost
half the one deduced using a constant limiting temperature.Comment: 11 pages, 6 figure
Kinetic energy spectra for fragments and break-up density in multifragmentation
We investigate the possibility, in nuclear fragmentation, to extract
information on nuclear density at break-up from fragment kinetic energy spectra
using a simultaneous scenario for fragment emission. The conclusions we derive
are different from the recently published results of Viola et al. [Phys. Rev.
Lett. 93, (2004), 132701] assuming a sequential fragment emission and claiming
that the experimentally observed decrease of peak centroids for kinetic energy
spectra of fragments with increasing bombarding energy is due to a monotonic
decrease of the break-up density.Comment: 6 pages, 3 figure
Advancement in the understanding of multifragmentation and phase transition for hot nuclei
Recent advancement on the knowledge of multifragmentation and phase
transition for hot nuclei is reported. It concerns i) the influence of radial
collective energy on fragment partitions and the derivation of general
properties of partitions in presence of such a collective energy, ii) a better
knowledge of freeze-out properties obtained by means of a simulation based on
all the available experimental information and iii) the quantitative study of
the bimodal behaviour of the heaviest fragment charge distribution for
fragmenting hot heavy quasi-projectiles which allows, for the first time, to
estimate the latent heat of the phase transition.Comment: 9 pages, Proceedings of IWM09, November 4-7, Catania (Italy
Status and performances of the FAZIA project
FAZIA is designed for detailed studies of the isospin degree of freedom,
extending to the limits the isotopic identification of charged products from
nuclear collisions when using silicon detectors and CsI(Tl) scintillators. We
show that the FAZIA telescopes give isotopic identification up to Z25
with a E-E technique. Digital Pulse Shape Analysis makes possible
elemental identification up to Z=55 and isotopic identification for Z=1-10 when
using the response of a single silicon detector. The project is now in the
phase of building a demonstrator comprising about 200 telescopes
Break-up stage restoration in multifragmentation reactions
In the case of Xe+Sn at 32 MeV/nucleon multifragmentation reaction break-up
fragments are built-up from the experimentally detected ones using evaluations
of light particle evaporation multiplicities which thus settle fragment
internal excitation. Freeze-out characteristics are extracted from experimental
kinetic energy spectra under the assumption of full decoupling between fragment
formation and energy dissipated in different degrees of freedom. Thermal
kinetic energy is determined uniquely while for freeze-out volume - collective
energy a multiple solution is obtained. Coherence between the solutions of the
break-up restoration algorithm and the predictions of a multifragmentation
model with identical definition of primary fragments is regarded as a way to
select the true value. The broad kinetic energy spectrum of He is
consistent with break-up genesis of this isotope.Comment: 17 pages, 5 figure
Alpha-particle clustering in excited expanding self-conjugate nuclei
The fragmentation of quasi-projectiles from the nuclear reaction 40Ca + 12C
at 25 MeV/nucleon was used to produce alpha-emission sources. From a careful
selection of these sources provided by a complete detection and from
comparisons with models of sequential and simultaneous decays, strong
indications in favour of -particle clustering in excited 16O, 20Ne and
24}Mg are reported.Comment: 8 pages, 4 figures, 12th International Conference on Nucleus-Nucleus
collisions (NN2015), 21-26 June 2015, Catania, Ital
Liquid-gas phase transition in hot nuclei studied with INDRA
Thanks to the high detection quality of the INDRA array, signatures related
to the dynamics (spinodal decomposition) and thermodynamics (negative
microcanonical heat capacity) of a liquid-gas phase transition have been
simultaneously studied in multifragmentation events in the Fermi energy domain.
The correlation between both types of signals strongly supports the existence
of a first order phase transition for hot nuclei.Comment: 9 pages, 2 figures, Invited talk to Nucleus-nucleus 2003 Moscow June
200
Photometric quality of Dome C for the winter 2008 from ASTEP South
ASTEP South is an Antarctic Search for Transiting Exo- Planets in the South
pole field, from the Concordia station, Dome C, Antarctica. The instrument
consists of a thermalized 10 cm refractor observing a fixed 3.88\degree x
3.88\degree field of view to perform photometry of several thousand stars at
visible wavelengths (700-900 nm). The first winter campaign in 2008 led to the
retrieval of nearly 1600 hours of data. We derive the fraction of photometric
nights by measuring the number of detectable stars in the field. The method is
sensitive to the presence of small cirrus clouds which are invisible to the
naked eye. The fraction of night-time for which at least 50% of the stars are
detected is 74% from June to September 2008. Most of the lost time (18.5% out
of 26%) is due to periods of bad weather conditions lasting for a few days
("white outs"). Extended periods of clear weather exist. For example, between
July 10 and August 10, 2008, the total fraction of time (day+night) for which
photometric observations were possible was 60%. This confirms the very high
quality of Dome C for nearly continuous photometric observations during the
Antarctic winter
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