Spectroscopy of exotic nuclei

Lecture 1

Reiner Krücken

Physik Department E12Technische Universität München

Maier-Leibnitz Laboratory of TU München and LMU Münchenfor Nuclear-, Particle-, and Accelerator Physics

R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 1

Outline

• Introduction– Central questions of the Physics of Exotic Nuclei– Production of radioactive ion beams

• Selected Topics in the Physics of Exotic Nuclei

– Nuclear Shell Structure and its Modifications in Exotic nuclei

– Halos, Skins and Pygmy Resonances

– Superheavy Nuclei

– Shape coexistence

Aim of the lectures: Discussion of current physics questions in combination with an introduction to various experimental methods

R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 1

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From QCD to atomic nuclei

u ud

Quarks,

Gluons

nucleon-nucleoninteraction

(ab-initio Models)

Light nuclei

(A10)?

QCD

Protons,

Neutrons

R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 1

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Ab-initio calculations of light nuclei

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7500 CPU hours

From QCD to atomic nuclei

u ud

Quarks,

Gluons

nucleon-nucleoninteraction

(ab-initio Models)

Light nuclei

(A10)

?

?

Heavy nuclei

effectivenucleon-nucleon

interaction

(Mean-field theories)

QCD

Protons,

Neutrons

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The Nuclear Landscape

Source: NUCLEUS A Trip Into The Heart of Matter

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Lecture 1

Bethe and von Weizäcker -1935

A)δ(Z,

A

2ZAa

A

ZaAaAaB

2

A1/3

2

c2/3

sv

Volumeenergy

Surfaceenergy

Coulombenergy

Asymmetryenergy

Pairingenergy

BindingEnergy

Coefficientsav = 15.56 MeVas = 17.23 MeVac = 0.697 MeVaA = 23.285 MevaP = 12.0 MeV

Semi-empirical mass formula

R = r0A1/3

Volume

Volume + Surface

Volume + Surface + Coulomb

Volume + Surface + Coulomb + Asymmetry

25020015010050

5

10

15

B/A

(M

eV

/nu

cle

on

)

Mass number A7

R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 1

Binding energy per nucleon

Saturation of binding due toshort range of NN interaction

Maximal binding around Fe Synthesis up to Fe via fusion in stars heavy elements are produced differently (n-capture) Fission and alpha decay are possible

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Lecture 1

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Shell effects in the binding energies

Mexp –

MW

eiz

säck

er

?

?

R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 1

Shell structure in nuclei and metal clusters

Annu. Rev. Nucl. Part. Sci. 2001 , Vol. 51: 219-259. H.O. + L2 +

L•S

2

8

20

28

50

82

126

184198

138

92

58

40

20

8

2

20

8

2

112

70

40

168

S.G. Frauendorf, C. Guet

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Lecture 1

Central Questions in Nuclear Structure Physics

• Where are the limits of nuclear stability?• How does shell structure change far from stability?• What are the phases, relevant degrees of freedom, and symmetries of the nuclear many-body system?

• Are there new modes of collective excitation?

• How are the Heavy Elements produced? Unified theoretical framework

with predictive power

Diversified experimental strategy to understand the Structure and Dynamics of Exotic Nuclei:

Measure Ground State Properties Gamma-ray spectroscopy of excited

states Reaction studies

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Lecture 1

Valley of stability & the limits of stability

En

erg

y

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Lecture 1

r-process and shell structure

Nuclear shell structure- Defines r-process path- Imprinted in abundance pattern- maybe modified for exotic nuclei

- Fission may fill the holes- Depends on shell structure

r - process

G. Martinez-Pinedo et al.

Pfeiffer et al.

40 50 60 70 80 90-2

-1

0

1

element number

abun

danc

e lo

g(X

/H)-

12

CS22892-052 (Sneden et al. 2003)

solar r

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Lecture 1

Production of radioactive ion beams

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How to produce and study Exotic Nuclei

Spectroscopic Methods:g- ray and particle spectroscopy following• Decay spectroscopy• Coulomb excitation• One- and Multi-nucleon transfer• knockout-reactions• Secondary fragmentation

Production of radioactive ion beams:• in-flight production• Isotope Separation On-Line

What can be measured? • existence of nuclei• masses, radii, half-lives • Excited states: energies, quantum numbers, transition matrix

elements , lifetimes, moments, single-particle occupations ...

R. Krücken - XVth UK Postgraduate School in Nuclear Physics – Lecture 1

Production of radioactive ion beams

Isotope Separation On-Line

Diffusion from thick target- depends on

chemistry- Needs time

Fragments move with beam velocity (30-90% c)

Reaction induced by light projectile (p,d,n) in thick target

Exotic nuclei are produced in thin target as fragment of heavy beam

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In-flight separation

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Lecture 1

In-flight production of radioactive beams

Projectile fragmentation or fission at high energies (50 -1000 AMeV)

Both fragments are highly excited ad evaporate

nucleons

Fig. by T. Glasmacher (NSCL/MSU)

Br - DE - Br Separation Method

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Lecture 1

UNILAC

SIS

FRS

ESR

100 m

Fragment Identification

DE

DE

TOF

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FAIR: Facility for Antiproton and Ion Research

Primary Beams

• 1012/s; 1.5-2 GeV/u; 238U28+

• Factor 100-1000 over present in intensity

Secondary Beams

• Broad range of radioactive beams

up to 1.5 - 2 GeV/u; • up to factor 10 000 in intensity over present

• Antiprotons 3 - 30 GeV

Storage and Cooler Rings

•Radioactive beams

•e- - A and Antiproton-A collider

100 m

UNILAC SIS 18

SIS 100/300

HESR SuperFRS

NESR

CRRESR

GSI todayGSI today

Future FacilityFuture Facility

ESR

1.4 GeV

ISOLDE at CERN

from PS Booster

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REX-ISOLDE

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FRIB in the U.S. (MSU/NSCL)

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Modifications of nuclear shell structure

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Two-neutron separation energies

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Fig. by R.F. Casten

Shellclosure

The extreme single-particle model

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StrongSpin-orbitFrom individual nuclei with NN interaction

to mean field with residual interaction

Penning Trap Mass Measurements

• Ingredients:– Homogeneous vertical magnetic field

® Radial trapping® cyclotron motion: wc= B q/m

– Axial electrostatic quadrupole field ® Vertical trapping® Vertical oscillation:

wz=(qU0/(md2))1/2

222

22

zcc

222

22

zcc

modified cyclotron motion:

4d2=(2z02+r0

2)

magnetron frequency:

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Lecture 1

Penning Trap Mass Measurements

yta

Vd

dx cos

22 xt

a

Vd

dy cos

22

Coupling between modes conversion to cyclotron motion

Excite cyclotron motion via quadrupole RF

Eject ions along trap axis transform radial energy to axial energy via dB/dz gradient

Measure time of flight (TOF) -the shorter TOF, the closer is the excitation frequency to the resonance

zBωμz,ωF dd

K. Blaum, Physics Reports 425 (2006) 1 – 78

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ISOLTRAP

A. Herlert, et al., Int. J. Mass Spectrom. 251, (2006) 131

bunching

measurement

purification

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