129 research outputs found
QCD analysis of Lambda hyperon production in DIS target-fragmentation region
We consider Lambda-hyperon production in the target-fragmentation region of
semi-inclusive deep-inelastic scattering within the framework of fracture
functions. We present a first attempt to determine the flavour and energy
dependences of these non-perturbative distributions through a simultaneous
QCD-based fit to available neutral- and charged-current semi-inclusive-DIS
cross sections. Predictions based on the resulting nucleon-to-Lambda fracture
functions are in good agreement with data and observables not included in the
regression. The successful prediction of the dependence of the Lambda
multiplicity notably represents the first validation of the perturbative
framework implied by fracture functions.Comment: Detailed comparison to quark-gluon string model added together with 3
additional plots. Three references added. Conclusions unchanged. Minor
corrections to the text. 18 pages, 18 figures, 3 table
Fission induced by nucleons at intermediate energies
Monte Carlo calculations of fission of actinides and pre-actinides induced by
protons and neutrons in the energy range from 100 MeV to 1 GeV are carried out
by means of a recent version of the Li\`ege Intranuclear Cascade Model, INCL++,
coupled with two different evaporation-fission codes, GEMINI++ and ABLA07. In
order to reproduce experimental fission cross sections, model parameters are
usually adjusted on available (p,f) cross sections and used to predict (n,f)
cross sections for the same isotopes.Comment: 36 pages, 18 figures, to appear in Nuclear Physics
Simultaneous fitting of statistical-model parameters to symmetric and asymmetric fission cross sections
peer reviewe
Influence of grains on the electromagnetic ac response of superconducting materials
2014 - 2015Type II superconducting materials are technologically interesting since they are characterized by the existence of a superconducting phase even after the penetration of the magnetic field inside them. In fact, while type I superconductors are characterized by a net transition from the perfect diamagnetic state (Meissner state) to the normal state, the magnetic field penetrates type II superconductors above a lower magnetic critical field in form of tubes of quantized magnetic flux, which are surrounded by vortices of superconducting currents, placed in a regular hexagonal lattice (mixed state or Abrikosov state). In this mixed state the superconductor can sustain the magnetic field and carry a current larger than in a type I superconductor. The superconducting phase persists below an upper magnetic critical field and a critical current density both depending on the temperature. In particular, the interaction of the superconducting vortices with the shielding currents and the external transport currents can generate dynamical phenomena which produce dissipation, and then increase the temperature and suppress the critical current density of the superconductor. On the other hand, these motion processes are hindered by the presence of defects which act as pinning centers of the vortices inside the lattice making the material able to sustain a current density below the critical value... [edited by author]XIV n.s
Unbiasedness and Optimization of Regional Weight Cancellation
The Monte Carlo method is often used to simulate systems which can be modeled
by random walks. In order to calculate observables, in many implementations the
"walkers" carry a statistical weight which is generally assumed to be positive.
Some random walk simulations, however, may require walkers to have positive or
negative weights: it has been shown that the presence of a mixture of positive
and negative weights can impede the statistical convergence, and special
weight-cancellation techniques must be adopted in order to overcome these
issues. In a recent work we demonstrated the usefulness of one such method,
exact regional weight cancellation, to solve eigenvalue problems in nuclear
reactor physics in three spatial dimensions. The method previously exhibited
had several limitations (including multi-group transport and isotropic
scattering) and needed homogeneous cuboid cancellation regions. In this paper
we lift the previous limitations, in view of applying exact regional
cancellation to more realistic continuous-energy neutron transport problems.
This extended regional cancellation framework is used to optimize the
efficiency of the weight cancellation. Our findings are illustrated on a
benchmark configuration for reactor physics.Comment: 19 pages, 5 figures, 2 appendice
Shell structure and few-nucleon removal in intranuclear cascade
It is well known that intranuclear-cascade models generally overestimate the
cross sections for one-proton removal from heavy, stable nuclei by a
high-energy proton beam, but they yield reasonable predictions for one-neutron
removal from the same nuclei and for one-nucleon removal from light targets. We
use simple shell-model calculations to investigate the reasons of this
deficiency. We find that a correct description of the neutron skin and of the
energy density in the nuclear surface is crucial for the aforementioned
observables. Neither ingredient is sufficient if taken separately.Comment: Presented at the 11th International Spring Seminar on Nuclear
Physics. To be published in Journal of Physics: Conference Serie
Extension of the Li\`ege Intranuclear-Cascade model to reactions induced by light nuclei
The purpose of this paper is twofold. First, we present the extension of the
Li\`ege Intranuclear Cascade model to reactions induced by light ions. Second,
we describe the C++ version of the code, which it is physics-wise equivalent to
the legacy version, is available in Geant4 and will serve as the basis for all
future development of the model. We describe the ideas upon which we built our
treatment of nucleus-nucleus reactions and we compare the model predictions
against a vast set of heterogeneous experimental data. In spite of the
discussed limitations of the intranuclear-cascade scheme, we find that our
model yields valid predictions for a number of observables and positions itself
as one of the most attractive alternatives available to Geant4 users for the
simulation of light-ion-induced reactions.Comment: Submitted to Phys. Rev.
Improving proton-induced one-nucleon removal in intranuclear cascade
It is a well-established fact that intranuclear-cascade models generally fail
to consistently reproduce the cross sections for one-proton and one-neutron
removal from stable nuclei by a high-energy proton beam. We use simple
shell-model calculations to investigate the reasons of this deficiency. We find
that a refined description of the neutron skin and of the energy density in the
nuclear surface is crucial for the aforementioned observables, and that neither
ingredient is sufficient if taken separately. As a by-product, the predictions
for removal of several nucleons are also improved by the refined treatment.Comment: 15 pages, 11 figures. Submitted to Phys. Rev.
Influence of nuclear de-excitation on observables relevant for space exploration
The composition of the space radiation environment inside spacecrafts is
modified by the interaction with shielding material, with equipment and even
with the astronauts' bodies. Accurate quantitative estimates of the effects of
nuclear reactions are necessary, for example, for dose estimation and
prediction of single-event-upset rates. To this end, it is necessary to
construct predictive models for nuclear reactions, which usually consist of an
intranuclear-cascade or quantum-molecular-dynamics stage, followed by a
nuclear-de-excitation stage.
While it is generally acknowledged that it is necessary to accurately
simulate the first reaction stage, transport-code users often neglect or
underestimate the importance of the choice of the de-excitation code. The
purpose of this work is to prove that the de-excitation model is in fact a
non-negligible source of uncertainty for the prediction of several observables
of crucial importance for space applications. For some particular observables,
the systematic uncertainty due to the de-excitation model actually dominates
the total uncertainty. Our point will be illustrated by making use of
nucleon-nucleus calculations performed with several
intranuclear-cascade/de-excitation models, such as the Li\`{e}ge Intranuclear
Cascade model (INCL) and Isabel (for the cascade part) and ABLA07, Dresner,
GEM, GEMINI++ and SMM (on the de-excitation side).Comment: 12 pages, 6 figures. Presented at the 38th COSPAR Scientific Assembly
(Bremen, Germany, 18-25 July 2010). Submitted to Advances in Space Researc
Experimental device-independent certified randomness generation with an instrumental causal structure
The intrinsic random nature of quantum physics offers novel tools for the
generation of random numbers, a central challenge for a plethora of fields.
Bell non-local correlations obtained by measurements on entangled states allow
for the generation of bit strings whose randomness is guaranteed in a
device-independent manner, i.e. without assumptions on the measurement and
state-generation devices. Here, we generate this strong form of certified
randomness on a new platform: the so-called instrumental scenario, which is
central to the field of causal inference. First, we theoretically show that
certified random bits, private against general quantum adversaries, can be
extracted exploiting device-independent quantum instrumental-inequality
violations. To that end, we adapt techniques previously developed for the Bell
scenario. Then, we experimentally implement the corresponding
randomness-generation protocol using entangled photons and active feed-forward
of information. Moreover, we show that, for low levels of noise, our protocol
offers an advantage over the simplest Bell-nonlocality protocol based on the
Clauser-Horn-Shimony-Holt inequality.Comment: Modified Supplementary Information: removed description of extractor
algorithm introduced by arXiv:1212.0520. Implemented security of the protocol
against general adversarial attack
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