176 research outputs found
Benchmarking GEANT4 nuclear models for hadron therapy with 95 MeV/nucleon carbon ions
In carbon-therapy, the interaction of the incoming beam with human tissues
may lead to the production of a large amount of nuclear fragments and secondary
light particles. An accurate estimation of the biological dose deposited into
the tumor and the surrounding healthy tissues thus requires sophisticated
simulation tools based on nuclear reaction models. The validity of such models
requires intensive comparisons with as many sets of experimental data as
possible. Up to now, a rather limited set of double di erential carbon
fragmentation cross sections have been measured in the energy range used in
hadrontherapy (up to 400 MeV/A). However, new data have been recently obtained
at intermediate energy (95 MeV/A). The aim of this work is to compare the
reaction models embedded in the GEANT4 Monte Carlo toolkit with these new data.
The strengths and weaknesses of each tested model, i.e.
G4BinaryLightIonReaction, G4QMDReaction and INCL++, coupled to two di fferent
de-excitation models, i.e. the generalized evaporation model and the Fermi
break-up are discussed
Simulation study on light ions identification methods for carbon beams from 95 to 400 MeV/A
Monte Carlo simulations have been performed in order to evaluate the
efficiencies of several light ions identification techniques. The detection
system was composed with layers of scintillating material to measure either the
deposited energy or the time-of-flight of ions produced by nuclear reactions
between 12C projectiles and a PMMA target. Well known techniques such as
(DELTA) E--Range, (DELTA) E--E--ToF and (DELTA)E--E are presented and their
particle identification efficiencies are compared one to another regarding the
generated charge and mass of the particle to be identified. The simulations
allowed to change the beam energy matching the ones proposed in an hadron
therapy facility, namely from 95 to 400 MeV/A
Double di ffential fragmentation cross sections measurements of 95 MeV/u 12C on thin targets for hadrontherapy
During therapeutic treatment with heavy ions like carbon, the beam undergoes
nuclear fragmentation and secondary light charged particles, in particular
protons and alpha particles, are produced. To estimate the dose deposited into
the tumors and the surrounding healthy tissues, an accurate prediction on the
fluences of these secondary fragments is necessary. Nowadays, a very limited
set of double di ffential carbon fragmentation cross sections are being
measured in the energy range used in hadrontherapy (40 to 400 MeV/u).
Therefore, new measurements are performed to determine the double di ffential
cross section of carbon on di erent thin targets. This work describes the
experimental results of an experiment performed on May 2011 at GANIL. The
double di ffential cross sections and the angular distributions of secondary
fragments produced in the 12C fragmentation at 95 MeV/u on thin targets (C,
CH2, Al, Al2O3, Ti and PMMA) have been measured. The experimental setup will be
precisely described, the systematic error study will be explained and all the
experimental data will be presented.Comment: Submitted to PR
Global analysis of the COVID-19 pandemic using simple epidemiological models
Several analytical models have been developed in this work to describe the evolution of fatalities arising from coronavirus COVID-19 worldwide. The Death or âDâ model is a simplified version of the well-known SIR (susceptible-infected-recovered) compartment model, which allows for the transmission-dynamics equations to be solved analytically by assuming no recovery during the pandemic. By fitting to available data, the D-model provides a precise way to characterize the exponential and normal phases of the pandemic evolution, and it can be extended to describe additional spatial-time effects such as the release of lockdown measures. More accurate calculations using the extended SIR or ESIR model, which includes recovery, and more sophisticated Monte Carlo grid simulations â also developed in this work â predict similar trends and suggest a common pandemic evolution with universal parameters. The evolution of the COVID-19 pandemic in several countries shows the typical behavior in concord with our model trends, characterized by a rapid increase of death cases followed by a slow decline, typically asymmetric with respect to the pandemic peak. The fact that the D and ESIR models predict similar results â without and with recovery, respectively â indicates that COVID-19 is a highly contagious virus, but that most people become asymptomatic (D model) and eventually recover (ESIR model)
Zero degree measurements of 12C fragmentation at 95 MeV/nucleon on thin targets
During therapeutic treatments using ions such as carbon, nuclear interactions
between the incident ions and nuclei present in organic tissues may occur,
leading to the attenuation of the incident beam intensity and to the production
of secondary light charged particles. As the biological dose deposited in the
tumor and the surrounding healthy tissues depends on the beam composition, an
accurate knowledge of the fragmentation processes is thus essential. In
particular, the nuclear interaction models have to be validated using
experimental double differential cross sections which are still very scarce. An
experiment was realized in 2011 at GANIL to obtain these cross sections for a
95 MeV/nucleon carbon beam on different thin targets for angles raging from 4
to 43{\deg} . In order to complete these data, a new experiment was performed
on September 2013 at GANIL to measure the fragmentation cross section at zero
degree for a 95 MeV/nucleon carbon beam on thin targets. In this work, the
experimental setup will be described, the analysis method detailed and the
results presented
Comparison of two analysis methods for nuclear reaction measurements of 12C +12C interactions at 95 MeV/u for hadrontherapy
During therapeutic treatment with heavier ions like carbon, the beam
undergoes nuclear fragmentation and secondary light charged particles, in
particular protons and alpha particles, are produced. To estimate the dose
deposited into the tumors and the surrounding healthy tissues, the accuracy
must be higher than (3% and1 mm). Therefore, measurements are
performed to determine the double differential cross section for different
reactions. In this paper, the analysis of data from 12C +12C reactions at 95
MeV/u are presented. The emitted particles are detected with
\DeltaEthin-\DeltaEthick-E telescopes made of a stack of two silicon detectors
and a CsI crystal. Two different methods are used to identify the particles.
One is based on graphical cuts onto the \DeltaE-E maps, the second is based on
the so-called KaliVeda method using a functional description of \DeltaE versus
E. The results of the two methods will be presented in this paper as well as
the comparison between both
The internal brakes on violent escalation:a typology
Most groups do less violence than they are capable of. Yet while there is now an extensive literature on the escalation of or radicalisation towards violence, particularly by âextremistâ groups or actors, and while processes of de-escalation or de-radicalisation have also received significant attention, processes of non- or limited escalation have largely gone below the analytical radar. This article contributes to current efforts to address this limitation in our understanding of the dynamics of political aggression by developing a descriptive typology of the âinternal brakesâ on violent escalation: the mechanisms through which members of the groups themselves contribute to establish and maintain limits upon their own violence. We identify five underlying logics on which the internal brakes operate: strategic, moral, ego maintenance, outgroup definition, and organisational. The typology is developed and tested using three very different case studies: the transnational and UK jihadi scene from 2005 to 2016; the British extreme right during the 1990s, and the animal liberation movement in the UK from the mid-1970s until the early 2000s
- âŠ