13,173 research outputs found
Measurement of fission cross-section of actinides at n_TOF for advanced nuclear reactors
No full textThe subject of this thesis is the determination of high accuracy neutron-induced fission cross-sections of various isotopes - all of which radioactive - of interest for emerging nuclear technologies. The measurements had been performed at the CERN neutron time-of-flight facility n TOF. In particular, in this work, fission cross-sections on 233U, the main fissile isotope of the Th/U fuel cycle, and on the minor actinides 241Am, 243Am and 245Cm have been analyzed. Data on these isotopes are requested for the feasibility study of innovative nuclear systems (ADS and Generation IV reactors) currently being considered for energy production and radioactive waste transmutation. The measurements have been performed with a high performance Fast Ionization Chamber (FIC), in conjunction with an innovative data acquisition system based on Flash-ADCs. The first step in the analysis has been the reconstruction of the digitized signals, in order to extract the information required for the discrimination between fission fragments and the background, as well as for the determination of the neutrons’s energy from their time-of-flight. Fission cross-sections for the various isotopes have been determined relative to the 235U(n,f) reaction, which is considered a standard of measurement in a wide energy range. In order to minimize systematic uncertainties, this reaction has been measured with the same detector and at the same time of the reactions subject of this thesis. A fundamental part of the thesis work has been the analysis of the 235U(n,f) reaction, which has allowed to study the response of the fission chamber, thanks also to the use of detailed Monte Carlo simulations performed with state-of-the-art codes for neutron transport and interaction. Moreover, the analysis of the 235U(n,f) reaction has allowed the energy calibration of the neutron beam, the determination of the incident neutron flux and an accurate estimate of the background. In the present thesis the final results for the 233U(n,f) cross-section are shown, as well as the preliminary results for the 241Am(n,f), 243Am(n,f) and 245Cm(n,f) cross-sections. The characteristics of the n TOF neutron beam have allowed to obtain results in a wide energy range, from about 30 meV to 1 MeV, in a single measurement. For the 233U(n,f) case, the final uncertainties on the cross-section are slightly larger than 3%, a value required for the development of innovative nuclear systems. In order to reach such an accuracy, corrections for sample-dependent efficiencies, as well as for reaction-related dead-time effects, have been applied. The thesis is organized as follows: Chapter 1 contains the motivations for the request of accurate fission cross-sections on actinides and on isotopes of interest for the Th/U fuel cycle. The main characteristics of the n TOF facility, in particular those relevant to fission measurements, are presented in Chapter 2. Chapter 3 contains a detailed description of the experimental apparatus used for the fission measurements. The study of the detector response, in particular in terms of detection efficiency and beam attenuation, is also presented. In Chapter 4, the analysis procedure used for data reduction, starting from the signals reconstruction procedure, is presented. The results for the 235U(n,f) and 238U(n,f) reaction, typically used as reference for fission measurements, are presented and discussed. Chapter 5 is dedicated to the determination of the 233U(n,f) cross-section. In this chapter, the detailed procedures used for background minimization, subtraction and corrections of experimental effects (detection efficiency and dead-time) are described. The extracted cross-sections, characterized by a very high accuracy (3%) in the entire energy range (from 30 meV to 1 MeV), are then compared with previous measurements and with cross-sections tabulated in evaluated data libraries. The comparison clearly shows the need to update the evaluations, in order to increase the reliability of the data required for the feasibility study and design of innovative nuclear systems based on the Th/U cycle. Chapter 6 presents the results, in some cases still preliminary, of the 241Am(n,f), 243Am(n,f) and 245Cm(n,f) reaction cross-sections. In this case, the very high background, associated with the natural radioactivity of the s amples, and the contaminations from other isotopes complicate the data analysis and result in an increased uncertainty on the extracted cross-sections. For the 243Am(n,f) reaction it has been possible to obtain accurate cross-sections only above 350 keV. In the other two cases, on the contrary, cross-sections in the entire neutron energy range from 30 meV to 1 MeV have been determined. Nevertheless, since it was not possible, in this work, to estimate with good accuracy the detection efficiency, due to the high background caused by the radioactivity, the extracted cross-sections have been normalized to the results of previous measurements or to tabulated cross-sections in conveniently chosen energy ranges. For this reason, the cross-sections obtained so far are still preliminary and affected by an uncertainty higher than that required for the development of Generation IV reactors for energy production and nuclear waste transmutation. Nonetheless, the present results are among the best currently available. It is reasonable that additional refinements in the analysis procedures and, eventually, measurements dedicated to the normalization problem will allow to improve the accuracy of the data shown in this thesis, up to the point required by the applications in the field of nuclear energy
Beam Intercepting Devices at CERN – Types, Challenges, Design, R&D and Operation
No full textBeam-intercepting systems are essential devices designed to absorb the energy and power of a particle beam. Generally, they are classified in three categories depending on their use: particle-producing devices, such as targets; systems for beam cleaning and control, such as collimators or scrapers; and those with safety functions, such as beam dumps or beam stoppers.
Beam-intercepting devices have to withstand enormous mechanical and thermally-induced stresses. In the case of the LHC beam dump, for example, upgrades of the LHC injectors will deliver a beam which at high energy will have a kinetic energy equivalent to 560 MJ during LHC Run 3, roughly corresponding to the energy required to melt 2.7 tonnes of copper. Released in a period of just 86 μs, this corresponds to a peak power of 6.3 TW or, put differently, 8.6 billion horse power.
The lectures will focus on the engineering activities regarding these devices, which consist in conceptual studies, material selection, prototyping and testing, R&D, design, manufacturing, installation and operation follow-up. Examples of recently developed devices will be shown, including fixed targets, collimators and dumps/absorbers to cope with LIU and HiLumi beams. Design work includes Monte Carlo (with code such as FLUKA) and Finite Element Analyses (FEA) to determine the behavior of the systems during beam impact, testing and prototyping activities to validate technical solutions, material characterisation and testing under beam, both single impact and long-term radiation damage.
Manufacturing, assembly and installation steps will be shown for some devices, including operation follow-up.
The challenges to be expected in the few years with the development and implementation of new machines will be also discussed.
Short bio of Marco Calviani
Marco Calviani (https://www.linkedin.com/in/marco-calviani-33265587/ ) is currently head of the Target Collimator Dumps Section at CERN, responsible for the conception, design, assembly, operation and maintenance of all the beam intercepting devices in the CERN’s accelerator complex, for current and future projects. He is also deputy head of the Sources Targets Interactions Group within the Systems Department. Marco is a nuclear and neutron physicist by education. He has led several projects in the last few years, including the design, construction and operation of the third generation n_TOF neutron spallation target as well as of the overall renovation of the antiproton production target area at CERN, which are currently operating and delivering physics. As TCD Section head he has been responsible for the delivery of several critical devices for the LHC Injector Upgrade project, including the new 300 kW SPS internal beam dump, as well as the upgrade of the LHC beam dump block in order to cope with the LHC Run3 total energy of 500 MJ/dump. The Section he is leading will be organizing the prototyping and procurement of more than 50 collimators for Long Shutdown 3 in the framework of the High-Luminosity Project as well as for new HL-LHC external dumps capable of accepting 700 MJ/dump. He is also involved in the conception of future beam intercepting devices for future CERN’s programs, including FCC, Muon Collider and Beam Dump Facility. Marco is serving in the ORNL STS Technical Advisory Committee as well as in several review panels for US, European and Japanese HEP and NP programs. Marco is author/co-authors of more than 100 papers (https://orcid.org/0000-0002-8213-8358 ).
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Beam Intercepting Devices at CERN – Types, Challenges, Design, R&D and Operation
No full textBeam-intercepting systems are essential devices designed to absorb the energy and power of a particle beam. Generally, they are classified in three categories depending on their use: particle-producing devices, such as targets; systems for beam cleaning and control, such as collimators or scrapers; and those with safety functions, such as beam dumps or beam stoppers.
Beam-intercepting devices have to withstand enormous mechanical and thermally-induced stresses. In the case of the LHC beam dump, for example, upgrades of the LHC injectors will deliver a beam which at high energy will have a kinetic energy equivalent to 560 MJ during LHC Run 3, roughly corresponding to the energy required to melt 2.7 tonnes of copper. Released in a period of just 86 μs, this corresponds to a peak power of 6.3 TW or, put differently, 8.6 billion horse power.
The lectures will focus on the engineering activities regarding these devices, which consist in conceptual studies, material selection, prototyping and testing, R&D, design, manufacturing, installation and operation follow-up. Examples of recently developed devices will be shown, including fixed targets, collimators and dumps/absorbers to cope with LIU and HiLumi beams. Design work includes Monte Carlo (with code such as FLUKA) and Finite Element Analyses (FEA) to determine the behavior of the systems during beam impact, testing and prototyping activities to validate technical solutions, material characterisation and testing under beam, both single impact and long-term radiation damage.
Manufacturing, assembly and installation steps will be shown for some devices, including operation follow-up.
The challenges to be expected in the few years with the development and implementation of new machines will be also discussed
Short bio Marco Calviani
Marco Calviani (https://www.linkedin.com/in/marco-calviani-33265587/ ) is currently head of the Target Collimator Dumps Section at CERN, responsible for the conception, design, assembly, operation and maintenance of all the beam intercepting devices in the CERN’s accelerator complex, for current and future projects. He is also deputy head of the Sources Targets Interactions Group within the Systems Department. Marco is a nuclear and neutron physicist by education. He has led several projects in the last few years, including the design, construction and operation of the third generation n_TOF neutron spallation target as well as of the overall renovation of the antiproton production target area at CERN, which are currently operating and delivering physics. As TCD Section head he has been responsible for the delivery of several critical devices for the LHC Injector Upgrade project, including the new 300 kW SPS internal beam dump, as well as the upgrade of the LHC beam dump block in order to cope with the LHC Run3 total energy of 500 MJ/dump. The Section he is leading will be organizing the prototyping and procurement of more than 50 collimators for Long Shutdown 3 in the framework of the High-Luminosity Project as well as for new HL-LHC external dumps capable of accepting 700 MJ/dump. He is also involved in the conception of future beam intercepting devices for future CERN’s programs, including FCC, Muon Collider and Beam Dump Facility. Marco is serving in the ORNL STS Technical Advisory Committee as well as in several review panels for US, European and Japanese HEP and NP programs. Marco is author/co-authors of more than 100 papers (https://orcid.org/0000-0002-8213-8358 ).</p
MABS validation through repeated execution and data mining analysis
No full textAgent Based Modelling is the most interesting and advanced approach for simulating a complex system: in a social context, the single parts and the whole are often very hard to describe in detail. Besides, there are agent based formalisms which allow to study the emergency of social behaviour with the creation and study of models, known as artificial societies. Thanks to the ever increasing computational power, it's been possible to use such models to create software, based on intelligent agents, which aggregate behaviour is complex and difficult to predict, and can be used in open and distributed systems. Data mining is born in the last decades in order to help users in finding useful knowledge from the otherwise overwhelming amount of data available nowadays from the web and the data collected every day by companies. Data Mining techniques can therefore be the keystone to reveal non-trivial knowledge expressed by the initial assumption used to build the micro-level of the model and the structure of the society of agents that emerged from the simulation
Facades of the Libreria di San Marco in Venice, The: An Interpretation of the Design Process
No full text"A new work in which I propose an interpretation of the design process Sansovino used to create the magnificent facades of the Libreria di San Marco in Venice, a masterpiece of Renaissance architecture." Sent to Marquand librarian by author Dec. 202
Art without an Author: Vasari’s Lives and Michelangelo’s Death
No full textMonografia sulla rappresentazione di Michelangelo nelle due edizioni delle Vite, sulla storia del libro e la questione della sua paternitàBook dedicated to the representation of Michelangelo in Vasari's Lives of the Artists, to the history of the book, and to the problem of its authorshi
How to prevent crimes using earthquakes
No full textIn this chapter the author describes how techniques coming from earthquakes prediction has been used to produce successful mathematical models useful in preventing crimes
Experimental results and strength model identification of pure iridium
No full textIntense and high energy proton beams are impacted with fixed materials (targets) in order to produce new
particles and secondary beams at CERN. In some of these targets, the requirement of reaching high yield
production of secondary particles points out to the use of high density materials. The interaction of the
beam with the atoms and nuclei of these materials produce extremely fast depositions of energy, highly
soliciting them from thermo-structural point of view due to subsequent rise of temperature and pressure
waves. Iridium is a good candidate material since exhibits very high density, high melting point, good
strength and stability at high temperature, and resistance to thermal shock.
The main goal of this study is the investigation of the mechanical behaviour at different temperatures and
strain-rates in tensile loading condition of pure iridium. A series of tests at room temperature at different
strain-rates (from 10-3 s-1 up to 104 s-1) was performed in order to obtain information about strain and
strain-rate sensitivity of the material. In addition, a series of tests at different temperatures in both quasistatic
and high strain-rate loading conditions was performed in order to obtain information about the
thermal softening of the material (from room temperature up to 1250 °C). The experimental data were
used to identify a strength model able to predict the material behaviour over wide ranges of variation of
the variables of interest
The Research Agenda: Marco Bassetto on the Quantitative Evaluation of Fiscal Policy Rules
No full textMarco Bassetto is a Senior Economist in the Economic Research Department at the Federal Reserve Bank of Chicago. He is interested in political-economy models of fiscal policy and in applications of game theory to the analysis of macroeconomic policy more in general. This piece reflects the personal views of the author and not necessarily those of the Federal Reserve Bank of Chicago or the Federal Reserve System.
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