451 research outputs found
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.
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
Engineering Semantic Self-composition of Services Through Tuple-Based Coordination
Service self-composition is a well-understood research area focusing on service-based applications providing new services by automatically combining pre-existing ones. In this paper we focus on tuple-based coordination, and propose a solution leveraging logic tuples and tuple spaces to support semantic self-composition for services. A full-stack description of the solution is provided, ranging from a theoretical formalisation to a technologically valuable design and implementation
Nucleon-induced reactions at intermediate energies: New data at 96 MeV and theoretical status
Double-differential cross sections for light charged particle production (up
to A=4) were measured in 96 MeV neutron-induced reactions, at TSL laboratory
cyclotron in Uppsala (Sweden). Measurements for three targets, Fe, Pb, and U,
were performed using two independent devices, SCANDAL and MEDLEY. The data were
recorded with low energy thresholds and for a wide angular range (20-160
degrees). The normalization procedure used to extract the cross sections is
based on the np elastic scattering reaction that we measured and for which we
present experimental results. A good control of the systematic uncertainties
affecting the results is achieved. Calculations using the exciton model are
reported. Two different theoretical approches proposed to improve its
predictive power regarding the complex particle emission are tested. The
capabilities of each approach is illustrated by comparison with the 96 MeV data
that we measured, and with other experimental results available in the
literature.Comment: 21 pages, 28 figure
Signals for a Transition from Surface to Bulk Emission in Thermal Multifragmentation
Excitation-energy-gated two-fragment correlation functions have been studied
between 2 to 9A MeV of excitation energy for equilibrium-like sources formed in
and p + Au reactions at beam momenta of 8,9.2 and 10.2 GeV/c.
Comparison of the data to an N-body Coulomb-trajectory code shows a decrease of
one order of magnitude in the fragment emission time in the excitation energy
interval 2-5A MeV, followed by a nearly constant breakup time at higher
excitation energy. The observed decrease in emission time is shown to be
strongly correlated with the increase of the fragment emission probability, and
the onset of thermally-induced radial expansion. This result is interpreted as
evidence consistent with a transition from surface-dominated to bulk emission
expected for spinodal decomposition.Comment: 11 pages including 3 postscript figures (1 color
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
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.
Multifragmentation of a very heavy nuclear system (I): Selection of single-source events
A sample of `single-source' events, compatible with the multifragmentation of
very heavy fused systems, are isolated among well-measured 155Gd+natU 36AMeV
reactions by examining the evolution of the kinematics of fragments with Z>=5
as a function of the dissipated energy and loss of memory of the entrance
channel. Single-source events are found to be the result of very central
collisions. Such central collisions may also lead to multiple fragment emission
due to the decay of excited projectile- and target-like nuclei and so-called
`neck' emission, and for this reason the isolation of single-source events is
very difficult. Event-selection criteria based on centrality of collisions, or
on the isotropy of the emitted fragments in each event, are found to be
inefficient to separate the two mechanisms, unless they take into account the
redistribution of fragments' kinetic energies into directions perpendicular to
the beam axis. The selected events are good candidates to look for bulk effects
in the multifragmentation process.Comment: 39 pages including 15 figures; submitted to Nucl. Phys.
Multifragmentation in Xe(50A MeV)+Sn Confrontation of theory and data
We compare in detail central collisions Xe(50A MeV) + Sn, recently measured
by the INDRA collaboration, with the Quantum Molecular Dynamics (QMD) model in
order to identify the reaction mechanism which leads to multifragmentation. We
find that QMD describes the data quite well, in the projectile/target region as
well as in the midrapidity zone where also statistical models can be and have
been employed. The agreement between QMD and data allows to use this dynamical
model to investigate the reaction in detail. We arrive at the following
observations: a) the in medium nucleon nucleon cross section is not
significantly different from the free cross section, b) even the most central
collisions have a binary character, c) most of the fragments are produced in
the central collisions and d) the simulations as well as the data show a strong
attractive in-plane flow resembling deep inelastic collisions e) at midrapidity
the results from QMD and those from statistical model calculations agree for
almost all observables with the exception of . This
renders it difficult to extract the reaction mechanism from midrapidity
fragments only. According to the simulations the reaction shows a very early
formation of fragments, even in central collisions, which pass through the
reaction zone without being destroyed. The final transverse momentum of the
fragments is very close to the initial one and due to the Fermi motion. A
heating up of the systems is not observed and hence a thermal origin of the
spectra cannot be confirmed.Comment: figures 1 and 2 changed (no more ps -errors
Spallation Neutron Production by 0.8, 1.2 and 1.6 GeV Protons on various Targets
Spallation neutron production in proton induced reactions on Al, Fe, Zr, W,
Pb and Th targets at 1.2 GeV and on Fe and Pb at 0.8, and 1.6 GeV measured at
the SATURNE accelerator in Saclay is reported. The experimental
double-differential cross-sections are compared with calculations performed
with different intra-nuclear cascade models implemented in high energy
transport codes. The broad angular coverage also allowed the determination of
average neutron multiplicities above 2 MeV. Deficiencies in some of the models
commonly used for applications are pointed out.Comment: 20 pages, 32 figures, revised version, accepted fpr publication in
Phys. Rev.
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