Nuclear Experiment W. Udo Schröder, 2008€¦ · W. Udo Schröder, 2008. Nuclear Experiment....

W. Udo Schröder, 2008

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Probes for Nuclear Processes

To “see” an object, the wavelength λ of the light used must be shorter than the dimensions d of the object. (DeBroglie: p=ħk=ħ2π/λ)Rutherford’s scattering experimentsdNucleus~ few 10-15 mNeed light of wave length λ [ 1 fm, or an energy E

( ) ( ) ( ) ( )

2

2 2 2 22

2 2

4 2 2

2

2002 6 1.21

( ) , . ., ( 1), 0.9 :

200 22 2 2 1.8

80 10 1 800

πλ

πλ

⋅= = = ≥ ⋅ =

= ≈

⋅= = = ≥ ⋅

⋅

⋅= =

p

p

c MeV fmE pc kc GeVfm

Massive m particle e g proton A m c GeV

k ck MeV fmpEm m Am c AGeV

MeV fm MeVAGeV fm A

Not easily available as light

Can be made with charged particle accelerators

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Elements of a Generic Nuclear Experiment

A: Study natural radioactivity (cosmic rays, terrestrial active samples)

B: Induce 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 Process

1. e- impact (gaseous ionization)• hot cathode arc• discharge in axial magnetic field (duo-

plasmatron)• electron oscillation discharge (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

“Venus”Making an e-/ion plasma

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Principle 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 equipotentialplates connected by resistor chain (R), ramping field down.

Typical for a CN:

7-8 MV terminal voltage

+

-

R

RR

R

RR

R

+

++

+

+

+

++

+

+

+

++

+

q+

Corona Points 20kV

+ HV Terminal

Ion Source

InsulatingAcceleration Tube/wEP plates

Charging Belt/ Pelletron

Ground Plate

Conducting Sphere

q+6


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“Emperor” (MP) Tandem

90o Deflection/Analyzing Magnet

Vacuum Beam Line

Ion Source

@Yale, BNL, TUNL, Florida, Seattle,…, Geneseo (small),…many around the world.

Munich University Tandem

Quadrupole Magnet

Pumping Station

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Charged Particles in Electromagnetic Fields

( )

( )

0

0

: ( ), ( )

. ,

0 :

,

,

ϖ

ϖ

= = = ⋅ ×

= ⋅ × ⊥

= ⋅ ⋅ =

= →

×

−

=

=

=

⋅ +

×

Lorentz Force fields electric E magnetic 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

q Bm

F

at rqB

p mv v r

Particle

q E v B

Cyclotron FrequencyB: Magnetic guiding field

vr

Charged particles in electromagnetic fields follow curvilinear trajectories used to guide particles “optically” with magnetic beam transport system

q

B

Independent of velocity or energy

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Electrodynamic Accelerators: Cyclotron

0

Cyclotron Frequencq B same for all vm

y

ϖ = −

ωfield

( ) 2max

2

2ε = = ⋅

qB

Maximum Ener

m

gy

qKR

A

Relativistic effects: m W = ε + moc2 shape B field to compensate. Defocusing corrected with sectors and fringe field.

+-E

Electrodynamic linear (LINAC) or cyclic accelerators(cyclotrons,synchrotons)

Cyclotrons at MIT, Berkeley, MSU, Texas A&M, …., many around the world (Catania, GANIL)

Acceleration, if ωfield = ω0Equilibrium orbit r: p = qBr

maximum pmax = qBR

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CERN Proton Linac10


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Experimental Setup: Neutron Time-of-Flight Measurement

Experiment at GANIL 29 A MeV 208Pb 197Au

Scatter Chamber

NeutronDetector

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Particle ID (Z , A, E) Specific energy loss, spatial ionization density, TOFNuclear Radiation Detectors

Si Telescope Massive Reaction Products SiSiCsI Telescope (Light Particles)

HeLiBe

NaNe

F

O

N

C

B

20Ne + 12C @ 20.5 MeV/u - θlab = 12°

ΔE

ΔE-E Telescope

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THE CHIMERA DETECTOR

Chimera mechanical structure 1m

1°

30°

REVERSE EXPERIMENTAL APPARATUS

TARGETBEAM

Experimental Method

ΔE-E ChargeΔE-E E-TOF Velocity, MassPulse shape Method LCP

Basic element Si (300μm) + CsI(Tl) telescope

Primary experimental observables

TOF δt ≤ 1 nsKinetic energy, velocityδE/E Light charged particles ≈2%Heavy ions ≤ 1%

Total solid angle ΔΩ/4π

94%

Granularity 1192 modules

Angular range 1°< θ < 176°

Detection threshold


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Secondary-Beam Facilities

2 principles:

A) Isotope Separator On LineDump 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 FlightInduce fragmentation/spallation reactions in thick production target, select reaction products for experimentation: reactions in 2nd target

GSI, RIKEN, MSU, Catania, (RIA)G. Raciti, 2005

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Secondary Beam Production

Bombard a Be target with 1.6-GeV 58Ni projectiles from SCC LNS Catania

Particle Identification Matrix ΔE x E

ΔEΔE

E

Particle

Target

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RIA: A New Secondary-Beam Facility

One of 2 draft designs : MSU/NSCL proposal

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ISOLDE Facility at CERN

Primary proton beam CERN-SPS

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Secondary-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 Separators

High Resolution SeparatorM

5000 30000MΔ

= →

General Purpose Separator

calculated

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Secondary 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 TrapISOLTRAP Ion motion in superposition of B and EQ fields has 3

cyclic components with frequencies ωC, ω+, ω-

Electric quadrupole field

0

qB

mϖ ϖ ω+ −= = +

Cyclotron frequency

Oscillating quadrupole field EQ can excite at ω = ω0 determine m

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Injection and Acceleration

Transfer to accelerator

Acceleration

Injection (axial)

Ion trajectory (cyclic)

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Slide Number 1Probes for Nuclear ProcessesElements of a Generic Nuclear ExperimentIonization ProcessElectron Cyclotron Resonance (ECR) Source Principle of Electrostatic Accelerators“Emperor” (MP) TandemCharged Particles in Electromagnetic FieldsElectrodynamic Accelerators: CyclotronCERN Proton LinacExperimental Setup: Neutron Time-of-Flight MeasurementNuclear Radiation DetectorsSlide Number 13Secondary-Beam FacilitiesSecondary Beam ProductionRIA: A New Secondary-Beam FacilityISOLDE Facility at CERNSecondary-Beam AcceleratorISOLDE Mass SeparatorsSecondary ISOLDE BeamsMass Measurement with Penning TrapInjection and Acceleration

Nuclear Experiment W. Udo Schröder, 2008€¦ · W. Udo Schröder, 2008. Nuclear Experiment....

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Transcript of Nuclear Experiment W. Udo Schröder, 2008€¦ · W. Udo Schröder, 2008. Nuclear Experiment....