近代核子物理實驗

中央研究院 物理所　章文箴2008/07/11 （五）

台大物理系 111 教室

2008 年雷射電漿物理暑期學校【電漿實驗專題】

Outline

• Discovery of nuclear structure• Development of “modern” nuclear physics

Nuclear structure at extreme and excited states Hadron physics with laser-electron photon

• Laser Nuclear Physics

Discovery of nuclear structure

A Wide Range of Scale in Observation

Mendeleev and Periodic Table

Models of Atom

Thomson model of atom

Rutherford model of atom

Rutherford experiment

•From angular distribution of rescattered -particles Rutherford concluded existence of positively charged core of atom then called nucleus

•The size of the nucleus was much smaller(10-14m) than size of the atom (10-10m)

Angular distribution of scattered -particles

Development of modern nuclear physics

Stable nuclei

Stable and decaying nuclei

All observed nuclei:- stable nuclei- decaying nuclei- particle emitting nuclei

proton-rich

neutron-rich

beta + proton neutron+ light particles

beta - neutron proton+ light particles

alpha emission of 4He2 protons + 2 neutrons

fission break-up of a nucleus two light nuclei

Nuclear Stability

Stable nuclei

Proton unstable

Neutron unstable

prot

ons

neutrons

Designer Nuclei in Nuclear Designer Nuclei in Nuclear LandscapeLandscape

82

50

28

28

50

82

2082

28

20stable nuclei

known nuclei

126

superheavynuclei

terra incognita

• How do protons and neutrons make stable nuclei and rare isotopes?

• What are properties of neutron matter?

• What are the heaviest nuclei that can exist?

• What is the origin of simple patterns in complex nuclei?

45Fe62Ga

11Li

225Ra

149Tb

134Sn

283112

101Sn

78Ni68Se

Radiation Detectors

• Photographic Film To detect , and radiations

• Spark counter To detect -particles

• Ionization Chamber To detect -particles

• Cloud Chamber To detect and particles

• Geiger-Müller Tube To detect , and radiations

What is an isomer ?

Metastable (long-lived) nuclear excited state.

‘Long-lived’ could mean

~10-19 seconds, shape isomers in alpha-clusters or

~1015 years 180Ta 9-->1+ decay.

Why/when do you get isomers?

If there is (i) large change in spin (‘spin-trap’)

(ii) small energy change

(iii) dramatic change in structure (shape, K-value)

Isomer ?

Excited State of Nuclei

Superdeformed Nuclei

• A band terminates when all valence particles outside a doubly magic (spherical) core are aligned

Astrophysical Consequences of Isomers

Ta is ‘stable’ in its isomeric state, but its ground state decays in hours!

Longstanding problem as to how the isomeric state is created in nature (via eg. S-process). Possible mechanism via heavier nuclei spallation or K-mixing of higher states in 180Ta.

+++++

---

--

225Ra

Over the last decade, tremendous progress has been made in techniques to produce designer nuclei, rare atomic nuclei with characteristics adjusted to specific research needs

45Fe

18F,22Na149Tb

nuclear nuclear structurestructure

astrophysicsastrophysics

applicationsapplications

tests of tests of fundamental fundamental

laws of naturelaws of nature

Some nuclei are more important than others

Medical Imaging - 99mTc

Technetium-99m a metastable isomer that decays into 99Tc by emission with a half-life of 6h.

Then decays into ruthenium by emission, but with a half-life of 2.1 x 105 years.

N.B. As a gamma emitter, 99mTc remains the same element during its residence in the body so it doesn’t change its chemistry when it decays.

99 9943 43mTc Tc

99 99 043 44 1Tc Ru e

Highly penetrating radiation.

Long half-life = low activity.

Gamma camera CT scanner

E.g. -camera image of 131I (from NaI solution) uptake in a normal and diseased thyroid gland, showing localisation of iodine.

E.g. tomographic image of a single anatomical level of the brain using 18F-labelled glucose.

Gamma spectroscopy

• Radiation interaction in scintillator produces light (may be in visible range)

• Quantification of output requires light amplification and detection device(s)

• This is accomplished with the: Photocathode Photomultiplier tube

• Both components are placed together as one unit optically coupled to the scintillator

880.P20 Winter 2006 Richard Kass

Photoelectric Effect absorbed by material, electron ejected

Compton Scatteringe-→e- “elastic scattering”

Pair Production→e+e- creates anti-matter

Basic Physics Processes in a Sodium Iodide (NaI) Calorimeter

e- e- e- e+

hv < 0.05 MeV 0.05 < hv < 10 MeV hv > 10 MeV -ray must have E>2me

The amount of light given off by NaI is proportional to the amount energy absorbed. The light yield is ~ 1 photon per 25 eV deposited in NaI, max=415 nm, decay time ~250nsec

NaI

radiation length of NaI ~2.5 cmbut only useful for E > few MeV

NaI is often used to measure the energy low gamma rays

Attenuation of the gamma rays is energy dependent

Scintillation detector

Gamma rayScintillationevent

Reflector housingFluor crystal NaI (Tl)

Photocathode

Photoelectrons

DynodesPhotomultiplier tube

Major components of PM Tube

• Photocathode material• Dynodes

electrodes which eject additional electrons after being struck by an electron

Multiple dynodes result in 106 or more signal enhancement

• Collector accumulates all electrons produced from final dynode

• Resistor collected current passed through resistor to generate

voltage pulse

Generalized Detection System using a Scintillator

Oscilloscope

Scaler

Multi-ChannelAnalyzer

DiscriminatorAmplifierPre-Amp

HighVoltage

Detector

(Crystal &Photomultiplier)

Material Density [g/cm3]

Emission Max [nm]

Decay Constant

(1)

Refractive Index (2)

Conversion Efficiency

(3)

Hygro-scopic

NaI(Tl) 3.67 415 0.23 s 1.85 100 yes

CsI(Tl) 4.51 550 0.6/3.4 s 1.79 45 no

CsI(Na) 4.51 420 0.63 s 1.84 85 slightly

CsIundoped 4.51 315 16 ns 1.95 4 - 6 no

CaF2 (Eu) 3.18 435 0.84 s 1.47 50 no

6LiI (Eu) 4.08 470 1.4 s 1.96 35 yes

6Li - glass 2.6 390 - 430 60 ns 1.56 4 - 6 no

CsF 4.64 390 3 - 5 ns 1.48 5 - 7 yes

(1) Effective average decay time For -rays.(2) At the wavelength of the emission maximum.(3) Relative scintillation signal at room temperature for -rays when coupled to a photomultiplier tube with a Bi-Alkalai photocathode.

Commonly Used Scintillators

Material Density [g/cm3]

Emission Maximum

[nm]

Decay Constant

(1)

Refractive Index (2)

Conversion Efficiency

(3)

Hygroscopic

BaF2 4.88 315 220

0.63 s0.8 ns

1.50 1.54

16 5 no

YAP (Ce) 5.55 350 27 ns 1.94 35 - 40 no

GSO (Ce) 6.71 440 30 - 60 ns 1.85 20 - 25 no

BGO 7.13 480 0.3 s 2.15 15 - 20 no

CdWO4 7.90 470 / 540 20 / 5 s 2.3 25 - 30 no

Plastics 1.03 375 - 600 1 - 3 s 1.58 25 - 30 no

(1) Effective agerage decay time For -rays.(2) At the wavelength of the emission maximum.(3) Relative scintillation signal at room temperature for -rays when coupled to a photomultiplier tube with a Bi-Alkalai photocathode.

Commonly Used Scintillators

Coincidence helps!

Coincidence Unit

Scaler

Multi-channelAnalyzer

Detector

Timing

Timing

Amplification

Detector

Source

Amplification

Gate

After Tsoulfanidis, 1995

Inner BGO ball at G.A.S.P.

ACACSS

BGO BGO BALBALLL

Projectile Fragmentation Reactions

hotspot

Excited pre-fragment

Finalfragment

projectile

target

Energy (velocity) of beam > Fermi velocity inside nucleus ~30 MeV/uCan ‘shear off’ different combinations of protons and neutrons.Large variety of exotic nuclear species created, all at forward angleswith ~beam velocity. Some of these final fragments can get trapped in isomeric states.

Problem 1: Isotopic identification. Problem 2: Isomeric identification.

Recoil – Decay –Tagging (RDT) method

Nucleonic matter

Hadronic Properties of GeV Photon

Vector-Meson Dominance Model

Energy loss by Bremsstrahlung (charge particles)

Effect plays a role only for e± and ultra-relativistic µ (>1000 GeV)

Ec(e-) in Cu(Z=29) = 20 MeV, Ec(µ) in Cu ≈ 1 TeV.muons in multi-GeV range can traverse thick layers of dense matter.

Bremsstrahlung

Laser-Electron-PhotonS facility

LEPS Facilities Worldwide

Laser-Electron-PhotonS facility

b) Laser hutch

a) Storage Ring

c) Experimental hutch

Compton -ray

Laser light

3.3 GeV electron Recoil electron

Tagging counter

Collision

Energy spectrum of

BCS photons

Bremsstrahlung

Backward-Compton scattering

Linearly Polarized Photon

• Backward Compton scattering with UV laser light• Intensity (typ.) : 2.5 * 106 cps• Tagging region : 1.5 GeV< E < 2.4 GeV• Linear polarization : 95 % at 2.4 GeV

E (Tagger) (GeV) E (GeV)

Cou

nts

Line

ar p

olar

izat

ion

Photon Flux

Laser and electron

Laser &Wavelength

Output Power

Repetition Rate

Pulse length

Electron Current & Energy

Photon Flux & Emax

SPring-8 Paladin 355 nm

8W 80MHz 5ps 100mA8 GeV

700 KHz2.5 GeV

TPS AVAI

266 nm3W 100KHz 25ns 300mA

3.3 GeV1.2 MHz0.6 GeV

Super Photon Ring 8 GeV (SPring-8)

Harima Science Garden City

SPring-8 Beam-Lines

Synchrotron Radiation

Ar ion laser (MLUV,CW 5.5W)

Polarizationrotator

Focusing lens

Laser System

e Collision in Storage Ring

Tagging counter

Bending magnet

Straight section

e’

Lasere- (8GeV)

Experimental Hutch

LEPS Detector System

1m

TOF wall

MWDC 2

MWDC 3

MWDC 1

Dipole Magnet (0.7 T) Start counter

Silicon VertexDetector

AerogelCherenkov(n=1.03)

nKKKn

Elementary Observables

• Momentum• Time-of-Flight• Energy Loss• Particle Identification• Invariant Mass Reconstruction

Momentum Measurements

• Definition Newtonian Mechanics

Special Relativity

• But how does one measure “p”?

mvp

mvp

21

1

cv

Momentum Measurements Technique

• Use a spectrometer with a constant magnetic field B.

• Charged particles passing through this field with a velocity “v” are deflected by the Lorentz force.

• Because the Lorentz force is perpendicular to both the B field and the velocity, it acts as centripetal force “Fc”.

• One finds

BvqFM

RmvFc

2

qBRmvp

Momentum Measurements Technique

• Knowledge of B (magnetic field) and R (bending radius) needed to get “p”

• B is determined by the construction/operation of the spectrometer.

• “R” must be measured for each particle.

Bending Magnet in Spectrometer

12 sinsin

/

/ dzBce

eqp yxz

Typical parameters: L=5~8 mm, d=2mm, wire=20m.

Secondary coordinate: Crossed wire planes; Charge division (resistive wires); Segmented cathode plane.

Address of fired wire(s) give one dimensional information.

d= 2mm(x)~600m

Multi Wire Proportional Chamber (MWPC)G.Charpak 1968 ,nobel prize 1992

Electric field E

BL

T vB

E

T 0

1 2 2

Drift Chambers

Target, Upstream Spectrometer, Dipole Magnet

LH2 Target (50 mm long)

Cherenkov Detector

SSDDrift Chamber

Start Counter

Dipole Magnet and Drift Chambers

tcL

cLt

Combine TOF with p (momentum measurement)

12

22

00 L

tcpmmp

Time-of-Flight (TOF) Measurements

Fast detectors : plastic scintillator

plastic scintillator,→generation→transmission of scintillation light→detection photomultiplier tube (expensive)

Organic Scintillator (plastics or liquid solutions)

Up to 10000 photons per MeVLow Z; ρ~1gr/cm3Doped, large choice of emission wavelength;ns decay times.Tracking, TOF, trigger, veto counters,sampling calorimeters.

Example: BC-408Rise time 0.9nsDecay time 2.1 nsWavelength length of Max. Emission 408nmRatio H:C 1.104

Time-of-Flight Wall

Particle Identification by TOF

Mass(GeV)

Mom

entu

m (G

eV)

K/ separation (positive charge)

K++

Mass/Charge (GeV)

Eve

nts

Reconstructed mass

d

p

K+

K-

+-

TOFlv

pvm ,

More Complex Observables

• Invariant Mass Reconstruction• Identification of decay vertices

Invariant Mass Reconstruction

• In special relativity, the energy and momenta of particles are related as follow

• This relation holds for one or many particles. In particular for 2 particles, it can be used to determine the mass of parent particle that decayed into two daughter particles.

42222 cmcpE

Pp1p

2p

Invariant Mass Reconstruction (cont’d)

• Invariant Mass

• Invariant Mass of two particles

• After simple algebra

22242 cpEcm PPP

221

221

42 cppEEcmP

cos2 22121

422

421

42 cppEEcmcmcmP

Signal of K+K-

Finding V0sproton

pion

Primary vertex

(1115) p+- Reconstruction

Requiring decay vertex (p-) outside target

Laser Nuclear Physics

ulis2007.celia.u-bordeaux1.fr/telechargement/Wednesday_AM/ULIS07_JG.ppt

Achievable Laser Intensity

Historical background About 20 years ago (1988), Boyer et al. Discuss

ed the possibility of inducing nuclear transitions using a laser

Discussion between K. Ledingham (Glasgow Univ.) and J. Magill (ITU) on the possibility of inducing 238U(,f)

First successful experiment at VULCAN, RAL (UK) in 2000, followed by NOVA, LLNL(USA)

Lasers entering nuclear science ...

bbbbbbbbbbbbb

Nuclear Reactions Triggered by LasersJETI chamber

PW VULCAN target chamber

30 TW LOA laser

UHI10 target chamber at SLIC

targ

et

The cascade process of energy transfer from the laser pulse to the radiations

• Primary processes are due to the action of the laser EM field on a plasma

• Fast electrons initiate secondary processes

TW laserpulse plasma

plasma

fast e-

1010 K

protons

ions

gamma rays

mono energetic gamma rays

positrons (anti matter)

fast neutrons

>1018 W/cm2>1018 W/cm2

Bremsstrahlung applications

• Multi-MeV electrons are stopped in thick high Z material

• They radiate typical bremsstrahlung rays (few 10 MeV)

• production of medical isotopes through transmutation

• studies of alternative research paths to classical reactor-induced reaction for transmutation purposes

• measurement of nuclear data

• diagnostic tools for plasma physic experiments

1018 1019 1020 1021 1022 1023 1024

1

10

100

1000

Jena

Recent experiemntal data PIC simulation (Esirkepov) Zagar et al. Extrapolation curve

Vulcan

Extrapolation curve

Max

imum

Pro

ton

Ener

gy (M

eV)

Laser Intensity × Wavelength Squared (Wm2/cm2)

Laser proton production

Maximum p+ energy is a function of I2

Emax = a(I2)

For I2 > 1019 :a ~ 4 or 3 x 10-9 MeV = 0.5

Mendonca, Spencer, 2000

Average proton energy is approximately 5 to 10 times smaller.

Higher efficiency: 10 % to 20% achievable (even 50 %)

High-intensity, ultra-fast laser pulse: 1020 W/cm2, λ ≈ 1 μm

Proton Beam Applications• Fast proton radiography (ns pulses)• Proton induced fission (p,f) measurement of

new cross sections on highly radioactive actinides

• Spallation related studies (Mc Kenna et al.) • Neutron source via (p,xn) reactions (Zagar et a

l.) • ITU project of H-loaded Pd film to optimize

yield and energy distribution of emitted protons

Other laser-driven ion beams ?

High-Intensity Laser Heavy Ion Acceleration

Radioactive ion beams Stable ion beams

Applications

Limits of nuclear stability“search for super heavies”

Production of radio pharmaceutical

Transmutation Heavy Ions for Space Propulsion

Actinide Nuclear Chemistry

High-Intensity Laser Heavy Ion Acceleration

Radioactive ion beams Stable ion beams

Applications

Limits of nuclear stability“search for super heavies”

Production of radio pharmaceutical

Transmutation Heavy Ions for Space Propulsion

Actinide Nuclear Chemistry

2,0x1019 4,0x1019 6,0x1019 8,0x1019 1,0x10200,1

1

10

C2+

Pb46+

D+ (gas jet)

C6+Al

C4+

C5+

F7+C6+

O

Al13+

Ene

rgy/

nucl

eon

(MeV

)

Laser Intensity (Wcm-2m2)

proton Emax scales as (I2)1/2

McKenna PRL 91

Zepf PRL 90

Pb36+

C3+

Clark PRL 85

C4+C5+

C3+ Hegelich PRL 89

Fritzler PRL 89

• Both radioactive and stable ion beams could be studied

40 MeV 16O ions,

120 MeV 35Cl ions,

500 MeV 208Pb ions

Heavy ion acceleration & applications

laser

focusing primary target:ion production, selection

and acceleration

ions

vacuum 10-4 mbar

Be sec. target holderand window

products

sec.

targ

et

He atmosphere

laser

focusing primary target:ion production, selection

and acceleration

ions

vacuum 10-4 mbar

Be sec. target holderand window

products

sec.

targ

et

He atmosphere

Be sample holder

accelerator

ion beam ions

vacuum 10-6 mbar

Be window

N2 cooling

products

targ

et

He atmosphere

Be sample holder

accelerator

ion beam ions

vacuum 10-6 mbar

Be window

N2 cooling

products

targ

et

He atmosphere

Comparison of two experimental designs for production and detection of super-heavy elements.

Laser induced neutron sources

Big Stationary Neutron Sources Flux [neutrons/cm2s] Traditional Reactor from 107 to 1013 High Flux Research Reactor up to 1015 Accelerator Driven Spallation up to 1014 Compact and Portable Neutron Sources Typical Source Strength

[neutrons/s] Radioactive Neutron Sources 105 to 107 Spontaneous Fission Sources around 1010 Portable Neutron Generators 108 to 1010 Lasers on Solid Targets Reaction(s)

Used Measured Source Strength [neutrons/shot]

Laser Energy [J/shot]

Lancaster 7Li(p,n)7Be 2×108 sr-1 69 Yang natZn(p,xn)Ga ≈ 1010 230 Yang 7Li(p,n)7Be 5×1010 230 Zagar natPb(p,xn)Bi 2×109 400

0 5 10 15 20 25 30 35104

105

106

107

108

109

10 20 30 40

109

1010

1011

1012 measured

Boltzmann fit (kT = 5 MeV)

Pro

tons

(1/M

eV)

Energy (MeV)

235U fission spectrum

Neu

trons

(1/M

eV)

Energy (MeV)

2x109 neutrons

Laser Generated Neutron Sources

Some General Properties• Compact Table-Top Sources (!)• Fast Neutrons – Broad Spectrum• Forward Directed Beams• Pulsed Operation • Very Short Pulse Durations (!)• High Repetition Rates• Useful Source Strengths

Conclusions and perspectives• Giant pulse single shot and high repetition rate tabletop lase

r have demonstrated their abilities to produced beam of electron and ions

• This research field is developing fast with fast development of high intensity laser

• Lasers do offer a new approach to studying material behavior under neutral and charge particle irradiation without resource to reactors or accelerators

• Currently laser light can directly accelerate electrons to relativistic speeds, and can consequently accelerate protons and other ions. In near future lasers will be able to accelerate protons to relativistic speeds directly

• New table-top radiation sources will become available• We have shown possible applications of laser accelerated e

lectrons, protons, gammas, neutrons• One can expect that these systems can be put to use as str

ong, and possibly compact sources, for nuclear applications.

END