Structure Studies of Unstable Nuclei by Electron Scattering

1. Electron scattering and nuclear structure2. a novel RI trap for electron scattering experiment

SCRIT (Self-Confining RI Target)3. R&D studies4. Summary

Toshimi SudaRIKEN, JAPAN

SCRIT collaboration:RIKEN : T. Emoto, S. Ito, T. Koseki, S. Nakamura,

T. Ohnishi, H. Takeda, M. Wakasugi and Y. YanoRikkyo Univ. : K. Kurita, H. Morikawa

Size and Shape of short-lived nucleiFundamental quantities such as m, τ

Nuclear (rms) radius : interaction cross sectionCharge (rms) radius : isotope shift

Nucleon distribution : hadron (proton) scattering Charge distribution : electron scattering

0

0.0005

0.001

0.0015

0.002

0 2 4 6 8 10

r(fm)

<r2>1/2 = 4.66 fm

ρ(r)

2.5

2.55

2.6

2.65

2.7

2.75

2.8

100 105 110 115 120 125 130 135

surf

ace

diffu

sene

ss (f

m)

Mass Number

132 Sn

Electron Scattering from unstable nuclei

• Most precise probe for structure studies• No electron scattering experiments from short-lived

nuclei, due to lack of their target.

elastic scattering => charge form factor

10-4

10-3

10-2

10-1

100

0 100 200 300 4000 100 200 300 400

Momentum transfer (MeV/c)

|F(q

)|2

a

r0

±5% ±10%

0 2 4 6 8 10

r0

ρ

4.4a0.9 ρ

0.1 ρ

0.5 ρ

Fermi distribution

r (fm)

Toy model

Form factor and required luminosity

Diffraction radius and surface diffuseness

L ~ 1027 ~ 1028 /cm2/s

At least the measurement must cover the first maximum of the form factor

100

101

102

103

104

105

106

100 200 300 400

Yie

ld (/

wee

k)

q (MeV/c)

Ee = 500 MeV

L=1028 /cm2/sΔΩ = 100 mSr

132Sn

high resolution spectrometerΔΩ~30 mSr

How to realize eRI scattering ?

(reltivistic)RI beam Recoiled

electronElectrontarget

3. RI-beam on “fixed” electron target

e-beam Trapped RI

Scattered electron

2. Electron + RI collider(GSI project)

Ee ~ a few 100 MeV

e RI

1.e-beam on “fixed” RI target

Ee ~ a few 100 MeV

γRI ~ a few 100

A novel method for eRI scattering SCRIT (Self-Confining RI Target)

Ion trapping : a well-known phenomena at e-storage ring.shorter beam life time, instability

Ion trapping + mirror potential for longitudinal trappingSpatially confined RI target

Numerical simulation

132Sn ions

expected luminosity

108 109 1010 1011107106

Injection rate (/s)

Ie = 500 mA

eRI facility based on the SCRIT concept

Electron storage ringSlow RI beam generator

1. In-flight facility + gas catcher 2. ISOL (γ+U fission) : A~100,130 n-rich nuclei

RI Ion generatorISOL and/or Gas catcher

Electron storage ring

SCRIT

Scattered electron

SCRIT Prototype

drift chamberplastic scintillatorsCaloriemeter

deflector

Ion source

Compensator

einzel lenz

slit

steerer

einzel lenz

SCRIT electrodes

Electron beam

Beam position monitor

0 50 100 cm

Ion Source(Cs1+)

SCRIT Electrodes

Scattered electron

e-beam

SCRIT Prototype

SCRIT : ~ a few π mm mradSurface ionizing Cs : < 10 π mm mrad

SCRIT electrodes for longitudinal trapping

42 electrodes toform various potential shape

Cs ion : 10 kVTrapping potential : 10 kV - δ

injection

trappiing

10000 2000

Feasibility study of the SCRIT schemeat KSR, Kyoto University

KSR, Kyoto Univ.

Ee = 100 MeVIe = 100 mAL ≥1026 /cm2 for N =107 /s

From e-linac

2m

γ-det

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Detector SetupLuminosity Monitoring

Bremsstrahlung : a set of BaF2 detector ~100bCharacteristic X-ray (30keV) : a Ge detector ~30bUltra-forward elastic scattering ~1000b

drift chamberplastic scintillatorcalorimeter

Electron detector

10-4

10-3

10-2

10-1

100

0 100 200 300

| Fc(q

)|2

Momentum Transfer (MeV/c)

Ee = 100 MeVθe ≥ 30 deg.Elastic scattering dominates.

First resultIon trapping by electron beam

Injec t ionDet ect ion

Gat e switching

Longitud ina l trap po tent ia l

-10

0

10

20

30

40

50

60

70

0 0.5 1 1.5

Ext

ract

ed io

ns si

gnal

(mV

)

Time (s)

0.3ms 1ms

10ms

100ms 1000ms

105

106

107

108

10-1 100 101 102 103 104

Num

ber

of d

etec

ted

ions

Trapping time (ms)

Detected charge

Number of detected ions

Summary

• Electron scattering will be a really unique tool to study the internal structure of unstable nuclei.

• SCRIT will be one of ways to realize eRI scattering experiment at next generation RIB facilities.

• SCRIT R&D is now underway. The trapping of externally injected ions has been confirmed.

• Next step is the accurate determination of luminosity. The detection of elastically scattered electrons from Cs will be also carried out..

BaF2 (bremss.)

Ion clearersGe-det.

Trapped Ion Analyzer

Ion clearers

R&D studies at KSREe = 100 MeVθe ≥ 30 deg.Elastic scattering dominates.Expected luminosity at KSR 1026/cm2/s for Nion=107

10-5

10-4

10-3

10-2

10-1

100

101

102

0 20 40 60 80 100

Cou

nts/

deg/

sec

Scattering Angle (deg.)

Ee = 100 MeV

L = 1025 /cm2/s

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e-beam

Electron - RI colliderPlanned in the GSI project

From H. Simon

SCRIT at RIBF (conceptual)Slow RI beam generator

1. Fragment separator + gas catcher2. ISOL (γ + U)

300MeV e-beam

50MeV e-beam 3550 6180

NIJI-II (modified) E=150～300MeV I=200mA L=～21m

SCRIT

ISOL

Pulse IS

50 kW132Sn 1011 /sec

UC2

DREPHA results

Distorted wave calculation

Momentum transfer (MeV/c)

dσ/dΩ

(cm

2 /Sr) Sn

Ee=300 MeVSnEe=300 MeV

0 100 200 300 4000 100 200 300 40010-31

10-30

10-29

10-28

10-27

10-26

10-25

10-24

ar0

4.5

4.55

4.6

4.65

4.7

4.75

4.8

100 105 110 115 120 125 130 135

RM

S ra

dius

(fm

)

Mass Number

Sn isotopes

132 Sn

J.R.Ficenec et al., Phys.Lett.42B('72)213.

2.5

2.55

2.6

2.65

2.7

2.75

2.8

100 105 110 115 120 125 130 135

surf

ace

diffu

sene

ss (f

m)

Mass Number

132 Sn