w. udo schröder, 2007 nuclear experiment 1. w. udo schröder, 2007 nuclear experiment 2 probes for...
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W. Udo Schröder, 2007
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Probes for Nuclei and Nuclear ProcessesProbes for Nuclei and Nuclear Processes
To “see” an object, the wavelength of the light used must be shorter than the dimensions d of the object. (DeBroglie: p=ħk=ħ2/Rutherford’s scattering experimentsdNucleus~ few 10-15 m ~ fm
Need light of wave length 1 fm, or photon energy
2 2 2 22
2 2
4 2 2
2
2002 6 1.2
1
200 2
2 2 2 1.8
8
( ) ,
0 10 1
. . :
81
0.
,
Matter waves massive m particle e g proto
c MeV fmE pc kc GeV
fm
k ck MeV fmpE
m m mc GeV
MeV fmGeV
G fmeV
n
Photons not easily available in nature
Can be made with charged particle accelerators
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Elements of a Generic Nuclear ExperimentElements of a Generic Nuclear Experiment
A: Studying natural radioactivity (cosmic rays, terrestrial active samples)
B: Inducing nuclear reactions in accelerator experiments
Particle Accelerator produces fast projectile nucleiProjectile nuclei interact with target nucleiReaction products are
a) collected and measured off line, b) measured on line with radiation detectors
Detector signals are electronically processed
Ion Source Accelerator Target
Detectors
Vacuum ChamberVacuum Beam Transport
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Ionization ProcessIonization Process
1. e- impact (gaseous ionization)
• hot cathode arc• discharge in axial magnetic field
(duo-plasmatron)• electron oscillation discharge
(Penning ion source) (PIG)• radio-frequency electrode-less
discharge (ECR)• electron beam induced discharge
(EBIS)
2. ion impact• charge exchange• sputtering
e-/ion beam
- +q-
discharge
-+q+
Acceleration possible for charged particles ionize neutral atoms
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Electron Cyclotron Resonance (ECR) Source Electron Cyclotron Resonance (ECR) Source
“Venus”
Making an e-/ion plasma
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Principle of Electrostatic AcceleratorsPrinciple of Electrostatic Accelerators
Van de Graaff, 1929
Operating limitations: 2 MV terminal voltage in air, 18-20 MV in pressure tank with insulating gas (SF6 or gas mixture N2, CO2)
Acceleration tube has equipotential plates connected by resistor chain (R), ramping field down.
Typical for a CN:
7-8 MV terminal voltage
+
-
R
R
R
R
R
R
R
+
++
+
+
+
+
+
+
+
+
+
+
+
q+
Charger 10 -4C/m2
Corona Points 20kV
+ HV Terminal
Ion Source
Acceler-ation Tube insulating
Charging Belt/ Pelletron
-Ground Plate
Conducting Sphere
+
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““Emperor” (MP) TandemEmperor” (MP) Tandem
MP Tandem15 MV
90o Deflection/Analyzing Magnet
Vacuum Beam Line
Ion Source
@Yale, BNL, TUNL, FSU, @Yale, BNL, TUNL, FSU, Seattle,…, SUNY Seattle,…, SUNY Geneseo,…Geneseo,…many around the world.many around the world.
Munich University TandemMunich University Tandem
Quadrupole Magnet
Pumping Station
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Charged Particles in Electromagnetic FieldsCharged Particles in Electromagnetic Fields
0
0
: ( ), ( )
. ,
0 :
,
,
Lorentz Force fields electric E magnetic B
F q E v B particle el charge q velocity v
E F p q v B
p q r B orbit radius r r B
pp q r B equilibrium orbit at r
qB
p mv v r
ParticleCyqB
mclotron Frequency
B: Magnetic guiding field
vr
Charged particles in electromagnetic fields follow curvilinear trajectories used to guide particles “optically” with magnetic beam transport system
q
B
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Electrodynamic Accelerators: CyclotronElectrodynamic Accelerators: Cyclotron
0
Cyclotron Frequenc
qB same for all v
m
y
field
2
max
2
2
qB
Maximum Ener
m
gy
qK
R
A
Relativistic effects: m W = + moc2 shape B field to compensate. Defocusing corrected with sectors and fringe field.
+-E
Electrodynamic linear (LINAC) or cyclic accelerators(cyclotrons,synchrotons)
Cyclotrons at BNL, LBL Berkeley, MSU, Texas A&M, …., many around the world (Catania, GANIL)
Acceleration, if field= 0
Equilibrium orbit r: p = qBr
maximum pmax = qBR
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11Experimental Setup: Neutron Time-of-Flight Experimental Setup: Neutron Time-of-Flight
MeasurementMeasurement
Experiment at GANIL 29 A MeV 208Pb 197Au
Scatter Chamber
Beam
Line
Ele
ctro
nic
s R
ack
NeutronDetector
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Particle ID: Resolution in Z , A, E
Nuclear Radiation DetectorsNuclear Radiation Detectors
Si Telescope Massive Reaction Products SiSiCsI Telescope (Light Particles)
HeLiBe
NaNe
F
O
N
C
B
20Ne + 12C @ 20.5 MeV/u - lab = 12°
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THE CHIMERA DETECTOR
THE CHIMERA DETECTOR
Chimera mechanical structure 1m
1°
30°
REVERSE EXPERIMENTAL APPARATUS
TARGETBEAM
Experimental Method
E-E ChargeE-E E-TOF Velocity, MassPulse shape Method LCP
Basic element Si (300m) + CsI(Tl) telescope
Primary experimental observables
TOF t 1 nsKinetic energy, velocityE/E Light charged particles 2%Heavy ions 1%
Total solid angle /4
94%
Granularity 1192 modules
Angular range 1°< < 176°
Detection threshold
<0.5 MeV/A for H.I. 1 MeV/A for LCP
CHIMERA characteristic features
688 telescopes
Laboratori del Sud, Catania/Italy
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Secondary-Beam FacilitiesSecondary-Beam Facilities
2 principles:
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,….
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
Primary Accelerator
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Secondary Beam ProductionSecondary Beam Production
Bombard a Be target with 1.6-GeV 58Ni projectiles from SCC LNS Catania
Particle Identification Matrix E x E
EE
E
Particle
Target
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RIA: A New Secondary-Beam FacilityRIA: A New Secondary-Beam Facility
One of 2 draft designs : MSU/NSCL proposal
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ISOLDE Facility at CERNISOLDE Facility at CERN
Primary proton beam CERN-PS
Project started @CERN in the 1960s
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Secondary-Beam AcceleratorSecondary-Beam Accelerator
Radiochemical goal (high-T chemistry, surface physics, metallurgy): produce ion beam with isotopes of only one element
Ion Source
Low-energy LINAC
Mass Separator
X1+
High Charge
Primary target: oven at 7000C – 20000C, bombarded with beams from 2 CERN accelerators (SC, PS).
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ISOLDE Mass SeparatorsISOLDE Mass Separators
High Resolution Separator
M5000 30000
M
General Purpose Separator
calculated
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Secondary ISOLDE BeamsSecondary ISOLDE Beams
Yellow: produced by ISOLDEn-rich, n-rich
Sn: A = 108 -142 low energy
O: A = 19 -22 low energy
Source: CERN/ISOLDE
ISOLDE accepts beams from several CERN accelerators (SC, PS)
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Mass Measurement with Penning TrapMass Measurement with Penning Trap
ISOLTRAP Ion motion in superposition of B and EQ fields has 3 cyclic components with frequencies C, +, -
Electric quadrupole field
0
qB
m
Cyclotron frequency
Oscillating quadrupole field EQ can excite at = 0 determine m
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Injection and AccelerationInjection and Acceleration
Transfer to accelerator
Acceleration
Injection (axial)
Ion trajectory (cyclic)