Transcript Slide 1
1 Nuclear Experiment W. Udo Schröder, 2007 Probes for Nuclear Processes 2 To “see” an object, the wavelength l of the light used must be shorter than the dimensions d of the object. (DeBroglie: p=ħk=ħ2p/l) Rutherford’s scattering experiments dNucleus~ few 10-15 m Need light of wave length l 1 fm, or an energy 200 MeV fm E pc kc 2p 6 1.2GeV l 1 fm c Not easily available Nuclear Experiment Massive (m) particle, e.g ., proton : k) ck ) 200 MeV fm ) 2p ) p E 2 2 2m 2m 2mc 1.8GeV l Can be made with 80 104 MeV 2 fm 2 1 800 MeV charged particle 2 GeV fm accelerators 2 W. Udo Schröder, 2007 2 2 2 2 Elements of a Generic Nuclear Experiment Nuclear Experiment 3 A: Studying natural radioactivity (cosmic rays, terrestrial active samples) B: Inducing nuclear reactions in accelerator experiments Particle Accelerator produces fast projectile nuclei Projectile nuclei interact with target nuclei Reaction products are a) collected and measured off line, b) measured on line with radiation detectors Detector signals are electronically processed Ion Source Vacuum Beam Transport Vacuum Chamber Accelerator Target Detectors W. Udo Schröder, 2007 Ionization Process Acceleration possible for charged particles ionize neutral atoms + 4 q+ discharge Nuclear Experiment + q- 1. e- impact (gaseous ionization) • hot cathode arc • discharge in axial magnetic field (duoplasmatron) • electron oscillation discharge (PIG) • radio-frequency electrode-less discharge (ECR) • electron beam induced discharge (EBIS) 2. ion impact • charge exchange • sputtering e-/ion beam W. Udo Schröder, 2007 Electron Cyclotron Resonance (ECR) Source Nuclear Experiment 5 “Venus” W. Udo Schröder, 2007 Making an e-/ion plasma Principle of Electrostatic Accelerators Conducting Sphere + + Ion 6 Source + + + Van de Graaff, 1929 + + + + + HV Terminal + Operating limitations: 2 MV terminal voltage in air, 18-20 MV in pressure tank with insulating gas (SF6 or gas mixture N2, CO2) + Charging Belt/ + Pelletron + Corona Points Nuclear Experiment + Acceleration Tube insulating Ground Plate q+ W. Udo Schröder, 2007 + 20kV - Acceleration tube has equipotential R plates connected R by resistor chain (R), ramping field R down. R Typical for a CN: R 7-8 MV terminal R voltage R “Emperor” (MP) Tandem Munich University Tandem Ion Source @Yale, BNL, TUNL, Florida, Seattle,…, SUNY Geneseo,… many around the world. 7 Pumping Station Quadrupole Magnet Nuclear Experiment Vacuum Beam Line W. Udo Schröder, 2007 90o Deflection/ Analyzing Magnet Charged Particles in Electromagnetic Fields Charged particles in electromagnetic fields follow curvilinear trajectories used to guide particles “optically” with magnetic beam transport system 8 Lorentz Force : fields electric ( E ), magnetic ( B ) B F q E v B r Nuclear Experiment q B: Magnetic guiding field W. Udo Schröder, 2007 v E 0: ) particle el. charge q, velocity v F p qv B p q r B orbit radius r , r B ) p p q r B , equilibrium orbit at r qB p mv v 0 r 0 q B Particle Cyclotron Frequency m Electrodynamic Accelerators: Cyclotron Electrodynamic linear (LINAC) Cyclotrons at MIT, Berkeley, MSU, Texas A&M, …., many around the world (Catania, or cyclic accelerators GANIL) (cyclotrons, synchrotons) Cyclotron Frequency 9 0 - + E Nuclear Experiment wfield q B m same for all v Acceleration, if wfield = w0 Equilibrium orbit r: p = qBr maximum pmax = qBR Maximum Energy max qBR ) 2m 2 q2 K A Relativistic effects: m W = + moc2 shape B field to compensate. Defocusing corrected with sectors and fringe field. W. Udo Schröder, 2007 Nuclear Experiment 10 CERN Proton Linac W. Udo Schröder, 2007 Experimental Setup: Neutron Time-of-Flight Measurement Experiment at GANIL 29 A MeV 208Pb 197Au Nuclear Experiment 11 Scatter Chamber W. Udo Schröder, 2007 Neutron Detector Nuclear Radiation Detectors SiSiCsI Telescope (Light Particles) 12 Particle ID: Resolution in Z , A, E Si Telescope Massive Reaction Products 20Ne + 12C @ 20.5 MeV/u - qlab = 12° Na Ne Nuclear Experiment F W. Udo Schröder, 2007 O N C B Be Li He THE CHIMERA DETECTOR Laboratori del Sud, Catania/Italy 13 CHIMERA characteristic features REVERSE EXPERIMENTAL APPARATUS 688 telescopes TARGET 30° Nuclear Experiment 1° Chimera mechanical structure 1m W. Udo Schröder, 2007 Experimental Method E-E Charge E-E E-TOF Velocity, Mass Pulse shape Method LCP Basic element Si (300m) + CsI(Tl) telescope Primary experimental observables TOF t 1 ns Kinetic energy, velocity E/E Light charged particles 2% Heavy ions 1% Total solid angle /4p 94% Granularity 1192 modules Angular range 1°< q < 176° Detection threshold <0.5 MeV/A for H.I. 1 MeV/A for LCP BEAM Secondary-Beam Facilities 2 principles: 14 A) Isotope Separator On Line Dump intense beam into very thick production target, extract volatile reaction products, study radiochemistry or reaccelerate to induce reactions in 2nd target (requires long life times: ms) GANIL-SPIRAL, EURISOL, RIA, TAMU,…. Nuclear Experiment B) Fragmentation in Flight Induce fragmentation/spallation reactions in thick production target, select reaction products for experimentation: reactions in 2nd target GSI, RIKEN, MSU, Catania, (RIA) G. Raciti, 2005 W. Udo Schröder, 2007 Secondary Beam Production Particle Particle Identification Matrix E x E Target 15 E E E Nuclear Experiment Bombard a Be target with 1.6-GeV 58Ni projectiles from SCC LNS Catania W. Udo Schröder, 2007 RIA: A New Secondary-Beam Facility Nuclear Experiment 16 One of 2 draft designs : MSU/NSCL proposal W. Udo Schröder, 2007 ISOLDE Facility at CERN Nuclear Experiment 17 Primary proton beam CERN-SPS W. Udo Schröder, 2007 Secondary-Beam Accelerator Radiochemical goal (high-T chemistry, surface physics, metallurgy): produce ion beam with isotopes of only one element 18 Primary target: oven at 7000C – 20000C, bombarded with beams from 2 CERN accelerators (SC, PS). Ion Source High Charge Nuclear Experiment X1+ W. Udo Schröder, 2007 Mass Separator Low-energy LINAC ISOLDE Mass Separators General Purpose Separator High Resolution Separator Nuclear Experiment 19 M 5000 30000 M W. Udo Schröder, 2007 calculated Secondary ISOLDE Beams Yellow: produced by ISOLDE Sn: A = 108 -142 low energy 20 n-rich, n-rich O: A = 19 -22 low energy Nuclear Experiment ISOLDE accepts beams from several CERN accelerators (SC, PS) Source: CERN/ISOLDE W. Udo Schröder, 2007 Mass Measurement with Penning Trap Ion motion in superposition of B and EQ fields has 3 cyclic components with frequencies wC, w+, w- 21 ISOLTRAP Nuclear Experiment Electric quadrupole field Cyclotron frequency 0 q B w m Oscillating quadrupole field EQ can excite at w = w0 determine m W. Udo Schröder, 2007 Injection and Acceleration 22 Ion trajectory (cyclic) Acceleration Nuclear Experiment Injection (axial) W. Udo Schröder, 2007 Transfer to accelerator 23 Nuclear Experiment W. Udo Schröder, 2007