Chẩn đoán vết nứt trong cần trục tháp bằng phương pháp thử nghiệm động TA

120 0 0
  • Chẩn đoán vết nứt trong cần trục tháp bằng phương pháp thử nghiệm động TA

Tài liệu hạn chế xem trước, để xem đầy đủ mời bạn chọn Tải xuống

Tài liệu liên quan

Thông tin tài liệu

Ngày đăng: 14/10/2021, 14:12

VIETNAM ACADEMY OF MINISTRY OF EDUCATION AND TRAINING SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY - LÊ TUẤN ANH STUDY ON PARAMETRIZATION OF PHOTOFISSION CROSS-SECTION OF 238 U AND OPTIMIZATION SIMULATION USING GEANT4 FOR DESIGN OF THE IGISOL FACILITY AT ELI-NP PROJECT PhD THESIS IN ATOMIC AND NUCLEAR PHYSICS Hanoi – 2021 ABSTRACT The main focus of the thesis will be the optimization simulation using Geant4 for the design of a Cryogenic Stopping Cell (CSC) for a future IGISOL (Ion guild Isotope separation On-line) facility at ELI-NP (the Extreme Light Infrastructure: Nuc-lear Physics) This proposed IGISOL facility will be dedicated to the study of exotic neutron-rich nuclei produced via photo ssion of U 238 target inside CSC A new reli- able empirical parametrization for total cross-section, mass yield, and isobaric charge distribution was developed in this study A Geant4-based code was implemented for the simulation of the photo ssion as well as the stopping of ssion fragments inside the target foils and Helium gas The simulation results have established the optimization of CSC’s parameters, as well as those of the target guration inside INTRODUCTION The Extreme Light Infrastructure (ELI), which is marked on the European Strategy Forum on Research Infrastructures (ESFRI) Roadmap as one of the prior-ity research infrastructure projects for Europe, will be the world’s rst international laser research infrastructure, pursuing unique science and research applications for international users ELI has three main research center located in three di erent coun-tries: ELI-Beamlines facility in the Czech, the ELI-ALPS facility in Hungary, and ELI-Nuclear Physics (ELI-NP) in Romania [1, 2, 3, 4] ELI-NP is expected to be the most advanced research facility in the world in the eld of photonuclear physics, and a new interdisciplinary research eld that brings together, for the rst time, high-power lasers and nuclear physics ELI-NP will o er a highly-polarized tunable mono-energetic beam in the range from 200 keV to 19.5 MeV This kind of beam will open new possibilities for high-resolution spectroscopy at higher nuclear excitation energies This will lead to a better understanding of nuclear structure at higher excitation energies with many doorway states, their damping widths and chaotic behaviour, but also new uctuating properties in the time and energy domain Besides, the ELI-NP gamma beam is also suitable for the production of the radioactive ion beam (RIB) through photo ssion of Uranium The advance in the understanding of nuclear structure far from stability using RIB is one of the top priorities de ned by the nuclear physicist community in the world To support this idea, an IGISOL (Ion guide isotope separation on-line) facility will be constructed to extract the photo ssion fragments to form RIBs at ELI-NP The heart of the IGISOL is a Cryogenic Stopping Cell (CSC), where the photo ssion process takes place At ELINP, the development of a CSC is considered [2, 5] For producing neutron-rich nuclei, designing nuclear physics experiments, as well as a target system in CSC, an accurate calculation for production cross-section of photo ssion fragments is crucial Therefore, it is necessary to develop a reliable tool for this job This tool will be useful for estimating the yield of neutron-rich nuclei from photo ssion process, designing nuclear physics experiments and many other applications not only at ELI-NP but also at other photo ssion facilities worldwide Moreover, It is important to series of prerequisite calculations and simulations to lead to the conceptual design for the particular case of the CSC at ELI-NP IGISOL facility The works in this thesis aim to ful ll two goals: i) the rst one is to develop a reliable empirical parametrization for the calculation of photo ssion cross-section over a wide energy range below 30MeV ii) The second one is to implement a Geant4-based code and carry out a series of simulations to optimize the design of CSC at ELI-NP This thesis is structured as follows In Chapter 1, the introduction of ELI and ELI-NP project is presented, as well as the photo ssion process, the methods for the production of RIB, and Geant4 toolkit Chapter is dedicated to describing the constructing process of the empirical parametrizations for total cross-section, mass yield and Isobaric charge distribution of 238 U photo ssion The works in Chapter will ful ll the rst goal Meanwhile, Chapter is dedicated to present the implementation of Geant4-based code and simulation results for optimizing the design of CSC, which will ful ll the second goal Finally, in the Conclusion part, a summary of this work is given Chapter OVERVIEW 1.1 The Extreme Light Infrastructure Nuclear Physics facility The Extreme Light Infrastructure (ELI) is a Research Infrastructure of PanEuropean interest ELI will be a multi-sited Research Infrastructure with complement-ary facilities located in the Czech Republic, Hungary, and Romania for the investigation of light-matter interactions at the highest intensities and shortest time scales [4] ELI-NP facility in Romania, which is one of the three pillars of the ELI, will develop a scienti c program using two beams of 10 PW laser and a Compton back-scattering (CBS) high-brilliance and intense low-energy gamma beam [1, 2, 3] The ELI- NP project consists of two main experimental areas: the ELI-NP HighPower Laser System (HPLS) and Gamma Beam System (GBS) Fig 1.1 expresses the sketch of ELI-NP machines and experimental areas The HPLS is designed for the following study cases [1, 2, 3]: The E1 Area host experiments of 10 PW laser with high density targets for production of extremely high uxes of protons and high-Z ions, as well as neutrons and their use in nuclear physics research and applications The E5 experimental area is dedicated for experiments of materials irradiation with simultaneous, mixed types of nuclear radiation produced by two PW/1 Hz laser beams The E6 experimental area will be dedicated to strong- eld quantum electrodynamics (QED) experiments Meanwhile, the study of photo ssion and the production of RIB are provided by the Gamma Beam System, and discussed in the following subsections Figure 1.1: Sketch of the ELI-NP machines and experimental areas HPLS High Power Laser System; OPCPA: Optical Parametric Chirped Pulse Ampli cation; XPW: Cross Polarised Wave system; LBTS: Laser Beam Transport System; GBS Gamma Beam System; DPSSL: Diode Pumped Solid State Laser; E1-E8 Experimental areas [3] 1.1.1 Gamma Beam System A highly-polarized ( 95%) tunable mono-energetic beams of spectral density of 10 photons=(s:eV ) in the range from 200 keV to 19.5 MeV with a bandwidth of 0:3% [3, 2, 5, 6] will be produced by ELI-NP GBS These beams will be produced through laser Compton backscattering (CBS) o an accelerated electron beam delivered by a linear accelerator The Compton backscattering (also called inverse Compton scattering) is considered as "photon accelerator" Fig 1.2 shows the geometry of the CBS between a laser photon E L energy, incident at angle L respect to the electron beam direction, and a relativistic electron with energy E e The energy of out-going Figure 1.2: Geometry of the inverse Compton scattering of a laser photon on a relativ-istic electron gamma scattered at an angle is given by E( )=2 e p where e = (ve=c) is the Lorentz factor for electron, ve is the electron velocity, me is the rest mass of the electron, and c is the speed of light Eq.(1.1) implies that by using a suitable collimator placed at certain angle, one can select the energy of gamma beam As shown in Fig 1.1, the ELI-NP gamma beam uses a green laser 0.4 J pulse energy with the wavelength = 515nm, corresponding to an incident photon energy EL = 2:4 eV The maximum energy, which a scattered photon can gain is achieved in head-on collisions, L = In case of ELI-NP gamma beam, with a given Ee, the maximum energy of gamma is [6]: E max (Ee) = 9:55eV (1 + Fig 1.3 presents two types of beams that will be delivered at ELI-NP The broad gamma beam displayed with blue dots has the energy range 10 18:5 MeV It was obtained by using Ee = 720M eV and collimating the beam below 0.7 mrad with a lead collimator The red dots in Fig 1.3 presents the pencil beam with the narrow energy range around 12.9 MeV The pencil beam was obtained by setting Ee = 600M eV and collimating the beam below 0.09 mrad The energy spectra of these two beam types are Figure 1.3: The simulated results for energy-angle correlation for two gamma beams: a broad beam up to 18.5 MeV collimated below 0.7 mrad (blue) and a pencil beam up to 12.9 MeV collimated below 0.09 mrad (red) The pencil beam is enclosed in a dashed red box for visibility [6] shown in Fig 1.4 The spectrum of broad gamma beam covers most of the Giant Dipole Resonance region of Uranium and Thorium [7], making it suitable for the production of exotic neutron-rich nuclei by photo ssion Meanwhile, the narrow beam-type will be suitable for experiments that demand a quasi-monochromatic gamma beam Bases on such kinds of gamma beams, ELI-NP GBS will provide the following experiments [10, 3]: NRF experiments: The Nuclear Resonance Fluorescence (NRF) technique is an outstanding tool for the investigation of low-lying dipole excitations in atomic nuclei and provides a speci c research niche for the ELI-NP facility In experiments, the pencil gamma beams scattered o bound nuclear state will provide access to targets that are available in small quantities and will open the actinide Figure 1.4: The energy spectra of the broad beam between 10{18.5 MeV (blue squares) and of the pencil beam at 12.9 MeV (red circles) from Fig 1.3 [6] region for NRF studies Photonuclear Reaction: The ELI-NP pencil beam makes it a precise tool for studies the characteristics of photonuclear reactions, such as cross-section, Iso- mer ratio, reaction yield Experiments above the Neutron Separation Threshold: The brilliant, narrowwidth, highly-polarized -ray beam will provide an opportunity to study the nuclear photo-response at and above the particle separation threshold, such as the pygmy dipole resonance (PDR) at and above the particle threshold, which is essential for nucleosynthesis in astrophysics [2, 11, 3] Nuclear Astrophysics Studies: The -induced nuclear reactions of astrophysical, such as Li( ; t) He, 16 12 O( ; ) C Photo ssion experiments and the production of RIB: Because of having an energy range that covers the whole Giant Dipole Resonant of Uranium and Thorium isotopes [1, 2, 7], the ELI-NP gamma beam is suitable for the produc-tion of the exotic neutron-rich isotopes in the Zr-Mo-Rh light fragment region and in the rare-earth heavy fragment region To support this idea, an IGISOL facility will be constructed at ELI-NP Some parts of the works in this thesis will help to form the conceptual design for this future IGISOL facility In fact, three exist three methods for the production of RIB The reason for choosing IGISOL technique is discussed below 1.2 Methods for production of RIB To address which method is suitable for producing RIB at ELI-NP, the details of each method will be discussed as following 1.2.1 The ISOL technique ISOL stands for Isotope Separation Online In the ISOL technique, the radioactive ion beams are produced via light-ion-induced spallation or ssion of a thick actinide target The ssion reactions can be induced by thermal neutrons, fast neutrons, protons or photons This method requires a high intensity of the primary beam and a thick hot target The great advantage of the thick targets is a large number of target atoms available for the production of the ions Even for such exotic nuclei with extremely low production cross-sections can still be obtained However, short-lived isotopes cannot be obtained because of the time required for di usion and e usion [12, 13, 14] Another disadvantage with ISOL production is that it is di cult to achieve high beam purity due to the many isobars of di erent elements produced simultaneously in the target Furthermore, refractory elements are in general di cult to produce due to the high temperatures required to make them volatile, see gure 1.6 [14] The general scheme of a typical ISOL facility is shown in Fig 1.5 The production of RIB by ISOL technique is summarized as follows: the primary beam hits the target to induce the nuclear reactions, the residual nuclei is di used to the 95 col_slit_rot[col_iter]->rotateZ( col_set_angle_span/col_set_slit_nb*(col_iter-1)); col_slit_pos_z[col_iter] = -col_set_mother_z/2 + col_min_dist + (col_iter-1)*col_slit_dist + (col_iter-1./2.)*col_slit_mother_z; new G4PVPlacement(col_slit_rot[col_iter], G4ThreeVector(0.,0.,col_slit_pos_z[col_iter]), col_slit_mother_log, "col_slit_mother", col_set_mother_log, false, 0, checkOverlaps);} G4RotationMatrix* col_set_rot[col_set_nb+1]; for(G4int col_iter = 1; col_iter rotateZ(col_set_phi_zero[col_iter]); new G4PVPlacement(col_set_rot[col_iter], G4ThreeVector(0.,0., ELIColl_z+(col_iter-1./2.)*col_set_mother_z+ (col_iter-1)*col_set_dist),col_set_mother_log, "col_set_mother", expHall_log, false, 0, checkOverlaps);}} // BUILDS THE ENTIRE CSC TARGET SYSTEM: void DetectorConstruction::BuildTargetSystem( G4LogicalVolume* logicCell, G4bool checkOverlaps) { G4double foilThick = runInput->GetFoilThick(); G4double backThick = runInput>GetBackThick(); // DEFINITION OF THE MATERIALS: G4NistManager* nist = G4NistManager::Instance(); // G4Material* m_targ = nist->FindOrBuildMaterial("G4_U"); G4Material* m_targ = nist->FindOrBuildMaterial("G4_URANIUM_DICARBIDE"); G4Material* m_back = nist->FindOrBuildMaterial("G4_GRAPHITE"); G4Material* m_fram = nist->FindOrBuildMaterial("G4_Al"); G4Material* m_rod = nist>FindOrBuildMaterial("G4_Fe"); // DEFINITION OF THE BASIC SHAPES: G4Box* TA_shape = new G4Box("TargetBox", 0.5*foilSize, 0.5*foilLength, 0.5*foilThick); 96 G4Box* BK_shape = new G4Box("BackingBox", 0.5*foilSize, 0.5*foilLength, 0.5*backThick); // THE 2D SHAPE OF THE FRAME FOR THE TARGET FOILS: G4double frameThick = foilThick + 2*backThick + 2*frameWidth; if(frameDepth>=frameLength) { G4cout
- Xem thêm -

Xem thêm: Chẩn đoán vết nứt trong cần trục tháp bằng phương pháp thử nghiệm động TA , Chẩn đoán vết nứt trong cần trục tháp bằng phương pháp thử nghiệm động TA