Download - Argonne National Laboratory is managed by The University of Chicago for the U.S. Department of Energy Birger Back Argonne National Laboratory The Radioactive.

Argonne National Laboratory is managed by The University of Chicago for the U.S. Department of Energy

Birger BackArgonne National Laboratory

The Radioactive Beam Program at Argonne

23rd Winter Workshop on Nuclear Dynamics

La Jolla, California

March 11-19, 2006

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Pioneering Science andTechnology Winter Workshop on Nuclear Dynamics, LaJolla March 11-19, 2006

B.B.Back, Argonne National Laboratory

Outline

• Physics Motivation for Radioactive Beams

• Past and Present Radioctive Beam Studies- Nuclear Astrophysics Studies (K.E.Rehm)- Light Nuclei & ab initio structure calculations

(A.H.Wuosmaa)- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)

• Future Plans- CARIBU: Accelerated 254Cf fission fragments (G. Savard)- Superconducting Solenoid Spectrometer (B.Back)- RIA ?

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Important physics questions

• modification of nuclear structure in neutron-rich systems- shell-structure quenching- single particle structure near neutron-rich magic nuclei- pairing interaction in weakly-bound systems

• collective behavior in neutron-rich systems

• r-process path- ground-state information

• mass• lifetime

- neutron capture rate- fissionability of very heavy neutron-rich isotopes

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Past and Present Radioactive Beam Studies

- Nuclear Astrophysics Studies (K.E.Rehm)

- Light Nuclei & ab initio structure calculations (A.H.Wuosmaa)

- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)

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ATLAS facility at Argonne

CARIBU

New additionbeing built Secondary beam

production target

Solenoid Spectrometer

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In-flight radioactive beams at ANL: e.g. 6He beams

7Li from ATLAS81 MeV

3 X 1011 particles/sec

D2 gas cell

7Li + 6He7Li

6He

Focusingsolenoid

Magneticseparator

Rebunchingresonator

7Li + 6He

7Li

*B. Harss, K. E. Rehm et al.,Rev. Sci. Instrum. 71, 380 (2000) 10,000 pps

Reaction: 7Li+d => 3He+6He

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Beams available“now”

Beams availableafter CARIBU upgrade

Radioactive beams at ATLAS

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RIA beams – delayed ‘til 2011 (Bodman)

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12C()16O

ANL: J. Greene, A. Hecht, D. Henderson, R. Janssens, C. L. Jiang,

E. F. Moore, M. Notani*, R. C. Pardo, K. E. Rehm, G. Savard,

J. P. Schiffer, B. Shumard, S. Sinha, X. D. Tang

Hebrew University: M. Paul

Northwestern University: L. Jisonna, R. E. Segel

Ohio University: C. Brune

University of North Carolina: A. Champagne

Western Michigan University: A. Wuosmaa *supp. by JINA

.. single most important nuclear physics uncertainty..

DoE Milestones: Reduce Uncertainties of the most crucial stellar evolution nuclear reactions (e.g. 12C()16O) by a factor of two.

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Need width of sub-threshold 1- stateto determins S-factor at Gamow window

Obtain width from interference structureon low-energy side of above-threshold 1- state

High intensity 16N beamDetector with no -sensitivity

Interference

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Twin-Ionization Chamber

Anode (Energy)

Frisch grid (angle)

Frisch grid

E()

16N(T½=7.1s)

anodeE(12C)

cathode

E ~ 1.82 MeV

No radiation damage

•Available with large areas

•Improved homogeneity

•Practically no sensitivity to ’s

•No dead layer

•Smaller pulse height defects

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Rotating wheel/cathode

4 Ionization chambers

16N beam

T ½=7.1 s

Stepping motor, encoder

Experimental setup

Rotating wheel, cathode

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16N 16O 12C+ first test results

PRELIMINARY

No background

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Example: 7He (Wuosmaa et al., PRC 72, 061301 (2005)

• 7He:- Unbound neutrons – halos – significant current interest- Theories generally agree but uncertainty in experimental results- Where is the 1st excited state? Is there one? What is it’s spin?

• Can be studied with (d,p) reactions using unstable beams

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Annular proton detectorslab ~ 3.5 srlab=109o-159o

Forward-angle EEdetectorslab=1o-7o

CD2 target540 g/cm2

Au Monitor target

Monitor EEtelescope

Beam axis

6He

proton

4,6He

Our secondary-beam intensities are ~1-5X104 particles/secEvent rate for 10 mb/sr ~ 10-50 counts/hour

Experimental setup

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Efficiency corrected data

Calibration Reaction 2H(7Li,p)8Lishowing empirical background

2H(6He,p)7He Fit with ground state,broad resonance, background

7He data with fit including state withEX=600 keV, =750 keV, Strength with expected spectroscopic factor

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- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)- L.-B. Wang,UIUC - APS/DNP Thesis prize (2006)

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Charge Radii MeasurementsCharge Radii Measurements

Methods of measuring nuclear radii (interaction radii, matter radii, charge radii)

Nuclear scattering – model dependent Electron scattering – stable isotope only Muonic atom spectroscopy – stable isotope only Atomic isotope shift

He-3 He-4 He-6 He-8

QMC Theory 1.74(1) 1.45(1) 1.89(1) 1.86(1)

-He Lamb Shift 1.474(7)

Atomic Isotope Shift 1.766(6) ? ?

p-He Scattering 1.95(10) GG 1.81(09) GO

1.68(7) GG 1.42(7) GO

RMS point proton radii (fm) from theory and experiment

G.D. Alkhazov et al., Phys. Rev. Lett. 78, 2313 (1997);D. Shiner et al., Phys. Rev. Lett. 74, 3553 (1995).

6He

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Experimental Setup - SchematicExperimental Setup - Schematic

PhotonCounter

RF dischargeKr, 4He

6He

He* Zeeman Slower MOT

TransversalCooling

389 nm 1083 nm

6HeProduced

Kr or 4HeCarrier gas

Mixingchamber

389 nm

2S-2P, 1083 nm

2S-3P, 389 nm

ATLAS12C(7Li,6He)13N

7Li3+: 100 pnA, 60 MeV

6He extracted: ~ 106 s-16He trapped: ~ 10-2 s-1

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Single AtomSingle AtomSpectroscopySpectroscopy

~ 150 6He atoms in one hour

April 6, 2004

4He

6He

-8 -6 -4 -2 0 2 4 6 80

200

400

600

800

1000

1200xc: 0.034 +/- 0.030 MHzw: 5.737 +/- 0.095 MHz

photo

n c

ounts

frequency (MHz)

-8 -6 -4 -2 0 2 4 6 850

100

150

200

250

300xc: -0.008 +/- 0.106 MHzw: 5.135 +/- 0.298 MHz

frequency (MHz)

photo

n c

ounts

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2.12.01.91.81.7

Point-Proton Radius of 6He (fm)

Tanihata et al 92

Alkhazov et al 97

Csoto 93

Funada et al 94

Varga et al 94

Wurzer et al 97

Esbensen et al 97

Pieper&Wiringa 01 (AV18 + IL2)

This work 04

Navratil et al 01

(AV18 + UIX)

(AV18)

Reaction collision

Elastic collision

Atomic isotope shift

Cluster models

No-core shell model

Quantum MC

Exp

erim

ents

The

orie

s

A Proving Ground for Nuclear Structure TheoriesA Proving Ground for Nuclear Structure TheoriesL.-B. Wang et al., Phys. Rev. Lett. 93, 142501 (2004) (Nucl-ex/0408008)

First model-independent determination

Pieper&Wiringa 05 (AV18+IL2)

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Outline




• Future Plans- CARIBU: Accelerated 254Cf fission fragments (G. Savard)- Superconducting Solenoid Spectrometer- RIA ?

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Neutron-rich ions for free – 252Cf spontaneous fission

r-process path

1 Ci 252Cf sourceabout 20% of total activity extracted as ionsworks for all specieslarge improvement over existing ISOL based facilities

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CARIBU – new building under construction

Courtesy: R. Pardo

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CARIBU:

Gas cell

RFQ cooler

ECR Charge breeder

Courtesy: R. Pardo

252Cf source

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Yields for Representative Species

Calculated maximum beam intensities for a 1 Ci 252Cf fission source using expected efficiencies.

Isotope Half-life (s)

Low-Energy BeamYield (s-1)

Accelerated BeamYield (s-1)

104Zr 1.2 6.0x105 2.1x104

143Ba 14.3 1.2x107 4.3x105

145Ba 4.0 5.5x106 2.0x105

130Sn 222. 9.8x105 3.6x104

132Sn 40. 3.7x105 1.4x104

138Xe 846. 9.8x106 7.2x105

110Mo 2.8 6.2x104 2.3x103

111Mo 0.5 3.3x103 1.2x102

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Outline




• Future Plans- CARIBU: Accelerated 254Cf fission fragments (G. Savard)- Superconducting Solenoid Spectrometer- RIA ?

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Measured quantitiesFlight time: Tflight=Tcyc

Position: zEnergy: Elab

Solenoidal spectrometer A new concept for studying light-ion reactions

Derived quantitiesPart. ID: m/qEnergy: Ecm

Angle: cm

Field: 5 Tesla

Particle Tcyc (ns)

p 13.1

d, 26.2

t 39.33He 19.7

/zqemVVmmE2

mV2zqe

2

1arccos

z2

qeVmVEE

T2

e

q

m

cm2cm

2lab

cmcm

cm2cm2

1labcm

flight

B

B

B

Β

p,d,t,3He,

Heavy-Ion

Inverse kinematics

Strong MRI magnet

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p(44Ti,p’)44Ti kinematics

Elab=50 keV z=1 mm Tflight=1 ns

Elab=50 keV =1 deg

10

8

6

4

2

0

30 40 50 60 70 80 90

p (degrees)

Ep

(Me

V)

10

8

6

4

2

0

=60o

z=25 cm

SimulationSimulation

Ep

(Me

V)

0 10 20 30 40 50

zp (cm)

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Acceptance

-acceptance: ~100%

(,Elab) acceptance depends on solenoid geometry and magnetic field strength

With the target located at the center of a 150 cm long solenoid of 50 cm bore theacceptance is shown here.

The lower energy cut-offarises from the outer diam.of the Si detector and itsproximity to the target (5cm)

Acceptance can be optimizedto specific reaction by movingtarget and Si detectors alongbeam axis

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Advantages of Solenoid Spectrometer

• Automatic particle I.D.

• Excellent center-of-mass energy resolution

• Large acceptance and solid angle

• Simple detector and electronics - few channels

• Excellent center-of-mass angle resolution

• Suppression of backgrounds

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Physics opportunities

• Single particle structure - Mapping out the single-particle strength near closed shells

• Astrophysics - Studies of the s, r, and rp-processes using (d,p) and (3He,d) reactions on

radioactive nuclei

• Pair transfer- Probing the nature of pair correlations in a new domain away from stability using (p,t), (t,p), and (3He,p) reactions

• Inelastic scattering- Study collective aspects of nuclear structure in radioactive species using p, , and other light particles

• Knockout reactions- Study of deep-lying particle orbits via (p,2p) reactions

• Surrogate reactions- Simulation of n-capture cross section on short-lived isotopes by comparison to (d,p) reactions. Needed for stockpile stewardship program

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Summary - Conclusions

• Present: Argonne has a substantial radioactive beam program- Nuclear Astrophysics- Structure of light nuclei – GFMC ab-initio theory- Laser spectroscopy – nuclear charge radii- Other

• Future:- CARIBU – weak but very neutron-rich beams- New Solenoid Spectrometer- RIA??? - National Academy of Science – Rare Isotope Science

Assessment Committee – see http://www7.nationalacademies.org/bpa/RISAC_Presentations.html

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Atomic Isotope ShiftAtomic Isotope Shift

Isotope Shift MSFS

Field shift:

due to nucleus size

FSr

Measured Calculated Measured Derived

IS(23S1 - 33P2) = 43,196.202(16) + 1.008(<r2>He4 - <r2>He6) MHz

---- G. W. F. Drake, Nucl. Phys. A737c, 25 (2004)

MS '

'

AA

AA

Mass shift:

due to nucleus recoil

Gordon Drake, High precision theory of atomic helium, Phys. Scripta T83: 83 (1999)

e-

e-

e-

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Layout

Solenoid: 50 cm bore x 150 cm long superconducting 5.0 Tesla axial field Cryo-coolers

Target: 1 mm thick cooled gas target w. Ti windowsSi-detectors: 12 pos. sensitive Si detectors 1x10 cmRecoil detectors: E-E Si array for A<20 recoils

Ionization chamber for heavier recoils

Solenoid

Si-detector array

Target wheel/cell

Vacuum chamber

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(d,p) Angular Distributions

2H(8Li,p)9Li DWBA calculations,QMC predictions, no normalization

2H(6He,p)7Heg.s. DWBA calculationsQMC calculations

Optical-model parameters from Schiffer et al, PRC 164

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sun

novae

neutron-star

supernovae

Supermassive stars

8B() 2

C(p,)8B

Na(p,)18Ne

15O()19Ne

17F(p,)14O

Ni(p,)57Cu

Ti(p)47V

Nuclear Astrophysics with Radioactive Beams:

PRL 84, 1651(2000)

PRL 80, 676(1998)

PRL 82, 3964(1999)

PRC 65, 035803(2002)

PRC 67, 065808(2003)

PRC 67, 065809(2003)

PRL 91, 252501(2003)

NPA 734, 615(2004)

C()16O

massive stars

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Energy Level FitsEnergy Level Fits+2n 6He+2n

8He+2n

S. Pieper and R. Wiringa