149 research outputs found
Geant4 simulations of soft proton scattering in X-ray optics. A tentative validation using laboratory measurements
Low energy protons (< 300 keV) can enter the field of view of X-ray space
telescopes, scatter at small incident angles, and deposit energy on the
detector, causing intense background flares at the focal plane or in the most
extreme cases, damaging the X-ray detector. A correct modelization of the
physics process responsible for the grazing angle scattering processes is
mandatory to evaluate the impact of such events on the performance of future
X-ray telescopes as the ESA ATHENA mission. For the first time the Remizovich
model, in the approximation of no energy losses, is implemented top of the
Geant4 release 10.2. Both the new scattering physics and the built-in Coulomb
scattering are used to reproduce the latest experimental results on grazing
angle proton scattering. At 250 keV multiple scattering delivers large proton
angles and it is not consistent with the observation. Among the tested models,
the single scattering seems to better reproduce the scattering efficiency at
the three energies but energy loss obtained at small scattering angles is
significantly lower than the experimental values. In general, the energy losses
obtained in the experiment are higher than what obtained by the simulation. The
experimental data are not completely representative of the soft proton
scattering experienced by current X-ray telescopes because of the lack of
measurements at low energies (< 200 keV) and small reflection angles, so we are
not able to address any of the tested models as the one that can certainly
reproduce the scattering behavior of low energy protons expected for the ATHENA
mission. We can, however, discard multiple scattering as the model able to
reproduce soft proton funneling, and affirm that Coulomb single scattering can
represent, until further measurements, the best approximation of the proton
scattered angular distribution at the exit of X-ray optics.Comment: submitted to Experimental Astronom
Microdosimetry of electrons in liquid water using the low-energy models of Geant4
The biological effects of ionizing radiation at the cellular level are frequently studied using the well-known formalism of microdosimetry, which provides a quantitative description of the stochastic aspects of energy deposition in irradiated media. Energy deposition can be simulated using Monte Carlo codes, some adopting a computationally efficient condensed-history approach, while others follow a more detailed track-structure approach. In this work, we present the simulation of microdosimetry spectra and related quantities (frequency-mean and dose-mean lineal energies) for incident monoenergetic electrons (50 eV-10 keV) in spheres of liquid water with dimensions comparable to the size of biological targets: base pairs (2 nm diameter), nucleosomes (10 nm), chromatin fibres (30 nm) and chromosomes (300 nm). Simulations are performed using the condensed-history low-energy physics models ( Livermore and Penelope ) and the track-structure Geant4-DNA physics models, available in the Geant4 Monte Carlo simulation toolkit. The spectra are compared and the influence of simulation parameters and different physics models, with emphasis on recent developments, is discussed, underlining the suitability of Geant4-DNA models for microdosimetry simulations. It is further shown that with an appropriate choice of simulation parameters, condensed-history transport may yield reasonable results for sphere sizes as small as a few tens of a nanometer
Geant4 simulation model of electromagnetic processes in oriented crystals for the accelerator physics
Electromagnetic processes of charged particles interaction with oriented
crystals provide a wide variety of innovative applications such as beam
steering, crystal-based extraction/collimation of leptons and hadrons in an
accelerator, a fixed-target experiment on magnetic and electric dipole moment
measurement, X-ray and gamma radiation source for radiotherapy and nuclear
physics and a positron source for lepton and muon colliders, a compact
crystalline calorimeter as well as plasma acceleration in the crystal media.
One of the main challenges is to develop an up-to-date, universal and fast
simulation tool to simulate these applications.
We present a new simulation model of electromagnetic processes in oriented
crystals implemented into Geant4, which is a toolkit for the simulation of the
passage of particles through matter. We validate the model with the
experimental data as well as discuss the advantages and perspectives of this
model for the applications of oriented crystals mentioned above.Comment: 18 pages, 9 figure
Electrocaloric Response of the Dense Ferroelectric Nanocomposites
Using the Landau-Ginzburg-Devonshire approach and effective media models, we
calculated the spontaneous polarization, dielectric, pyroelectric, and
electrocaloric properties of BaTiO core-shell nanoparticles. We predict
that the synergy of size effects and Vegard stresses can significantly improve
the electrocaloric cooling (2- 7 times) of the BaTiO nanoparticles with
diameters (10-100) nm stretched by (1-3)% in comparison with a bulk BaTiO.
To compare with the proposed and other known models, we measured the
capacitance-voltage and current-voltage characteristics of the dense
nanocomposites consisting of (28 -35) vol.% of the BaTiO nanoparticles
incorporated in the poly-vinyl-butyral and ethyl-cellulose polymers covered by
Ag electrodes. We determined experimentally the effective dielectric
permittivity and losses of the dense composites at room temperature. According
to our analysis, to reach the maximal electrocaloric response of the core-shell
ferroelectric nanoparticles incorporated in different polymers, the dense
composites should be prepared with the nanoparticles volume ratio of more than
25 % and fillers with low heat mass and conductance, such as Ag nanoparticles,
which facilitate the heat transfer from the ferroelectric nanoparticles to the
polymer matrix. In general, the core-shell ferroelectric nanoparticles
spontaneously stressed by elastic defects, such as oxygen vacancies or any
other elastic dipoles, which create a strong chemical pressure, are relevant
fillers for electrocaloric nanocomposites suitable for advanced applications as
nano-coolers.Comment: 38 pages, including 10 figures and 2 appendixe
Crisis Management and Communication Strategies: RUSALâs Case
No company is immune to crisis situations, an affirmation which, despite its triviality, is undeniably true. However, from the early 2014, such statement may have become even more true to Russian corporations, as the annexation of the Crimean Peninsula gave start to rounds of economic sanctions that are still perpetrated today. Such measures, which were initiated in response to the Kremlinâs political maneuvers, have hit a number of Russian companies, and increased the degree of uncertainty in which they have to operate, as they see economic restrictionâs impact not only on the business activity tangible factorsâi.e., economic rewards, service, and performanceâbut also on intangible factorsâi.e., image and reputationâas well. Crises are integral parts of all world systems, unfortunately. While they are a theoretically well-understood issue, in practice, crises are perceived as a very painful phenomenon. A crisis can be compared to riding a roller coaster. First, as we gain speed and climb up the tracks we are filled with a sense of joy and delight. These feelings are quickly replaced with anticipation, panic, and fear as the roller coaster plunges into the âabyss.
A Roadmap for HEP Software and Computing R&D for the 2020s
Particle physics has an ambitious and broad experimental programme for the coming decades. This programme requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment in the R&D of software to acquire, manage, process, and analyse the shear amounts of data to be recorded. In planning for the HL-LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that the efforts complement each other. In this spirit, this white paper describes the R&D activities required to prepare for this software upgrade.Peer reviewe
Development and validation of HERWIG 7 tunes from CMS underlying-event measurements
This paper presents new sets of parameters (âtunesâ) for the underlying-event model of the HERWIG7 event generator. These parameters control the description of multiple-parton interactions (MPI) and colour reconnection in HERWIG7, and are obtained from a fit to minimum-bias data collected by the CMS experiment at s=0.9, 7, and 13Te. The tunes are based on the NNPDF 3.1 next-to-next-to-leading-order parton distribution function (PDF) set for the parton shower, and either a leading-order or next-to-next-to-leading-order PDF set for the simulation of MPI and the beam remnants. Predictions utilizing the tunes are produced for event shape observables in electron-positron collisions, and for minimum-bias, inclusive jet, top quark pair, and Z and W boson events in proton-proton collisions, and are compared with data. Each of the new tunes describes the data at a reasonable level, and the tunes using a leading-order PDF for the simulation of MPI provide the best description of the dat
Validation of Physics Models of Geant4 Versions 10.4.p03, 10.6.p02 and 10.7.p01 using Data from the CMS Experiment
CMS tuned its simulation program and chose a specific physics model of Geant4 by comparing the simulation results with dedicated test beam experiments. Test beam data provide measurements of energy response of the calorimeter as well as resolution for well identified charged hadrons over a large energy region. CMS continues to validate the physics models using the test beam data as well as collision data from the Large Hadron Collider. Isolated charged particles are measured simultaneously in the tracker as well as in the calorimeters. These events are selected using dedicated triggers and are used to measure the response in the calorimeter. Different versions of Geant4 (10.2.p02, 10.4.p03, 10.6.p02) have been used by CMS for its Monte Carlo production and a new version (10.7.p01) is now chosen for future productions. A suitable physics list (collection of physics models) is chosen by optimizing performance against accuracy. A detailed comparison between data and Geant4 predictions is presented in this paper
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