1. The Radioactive Beam Program at Argonne
23rd Winter Workshop on Nuclear Dynamics
La Jolla, California
March 11-19, 2006
The Radioactive Beam Program at Argonne
Birger Back
Argonne National Laboratory
Test

2. 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 ?
Test

3. 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
Test

4. 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.)
Test

5. ATLAS facility at Argonne
Solenoid
Spectrometer
New addition
being built
Secondary beam
production target
CARIBU
Test

6. In-flight radioactive beams at ANL: e.g. 6He beams
Reaction: 7Li+d => 3He+6He
Rebunching
resonator
Focusing
solenoid
Magnetic
separator
D2 gas cell
7Li
7Li + 6He
7Li from ATLAS
81 MeV
3 X 1011 particles/sec
7Li + 6He
7Li
6He
*B. Harss, K. E. Rehm et al.,
Rev. Sci. Instrum. 71, 380 (2000)
10,000 pps
Test

7. Radioactive beams at ATLAS
Beams available
after CARIBU upgrade
Beams available
“now”
Test

8. RIA beams – delayed ‘til 2011 (Bodman)
- Huge range of nuclear structure to study with solenoid coupled to RIA
Test

9. 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.)
Test

10. 12C(a,g)16O .. single most important nuclear physics uncertainty..
DoE Milestones: Reduce Uncertainties of the most crucial stellar evolution nuclear reactions (e.g. 12C(a,g)16O) by a factor of two.
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
Test

11. Need width of sub-threshold 1- state
Interference
Need width of sub-threshold 1- state
to determins S-factor at Gamow window
Obtain width from interference structure
on low-energy side of above-threshold
1- state
High intensity 16N beam
Detector with no b-sensitivity
Test

12. Twin-Ionization Chamber
E(a)
Anode (Energy)
16N(T½=7.1s)
Frisch grid (angle)
Ea ~ 1.82 MeV
No radiation damage
Available with large areas
Improved homogeneity
Practically no sensitivity to b’s
No dead layer
Smaller pulse height defects
cathode
Frisch grid
anode
E(12C)
Test

13. Experimental setup 4 Ionization chambers Stepping motor, encoder
Rotating wheel/cathode
16N beam
T ½=7.1 s
Rotating wheel, cathode
Test

14. 16N 16O  12C+ a first test resultsb-
PRELIMINARY
No b background a
Test

15. 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.)

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

17. Experimental setup
Monitor EDE
telescope
Au Monitor target
proton
CD2 target
540 mg/cm2
Beam axis
6He
4,6He
Forward-angle EDE
detectors
qlab=1o-7o
Annular proton detectors
Wlab ~ 3.5 sr
qlab=109o-159o
Our secondary-beam intensities are ~1-5X104 particles/sec
Event rate for 10 mb/sr ~ counts/hour
Test

18. Efficiency corrected data
Calibration Reaction 2H(7Li,p)8Li
showing empirical background
2H(6He,p)7He Fit with ground state,
broad resonance, background
7He data with fit including state with
EX=600 keV, G=750 keV,
Strength with expected
spectroscopic factor
Test

19. 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.)
L.-B. Wang,UIUC
APS/DNP Thesis prize (2006)

20. Charge 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
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
Test

21. Experimental Setup - Schematic
ATLAS
12C(7Li,6He)13N
7Li3+: 100 pnA, 60 MeV
2S-2P, 1083 nm
2S-3P, nm
6He
Produced
389 nm
1083 nm
6He
MOT
Zeeman Slower
He*
Mixing
chamber
RF discharge
Kr, 4He
Transversal
Cooling
389 nm
Kr or 4He
Carrier gas
Photon
Counter
6He extracted: ~ 106 s-1
6He trapped: ~ 10-2 s-1
Test

22. Single Atom Spectroscopy
4He
6He
~ 150 6He atoms in one hour
April 6, 2004
Test

23. A Proving Ground for Nuclear Structure Theories
L.-B. Wang et al., Phys. Rev. Lett. 93, (2004) (Nucl-ex/ )
Reaction collision
Experiments
Elastic collision
First model-independent determination
Atomic isotope shift
Cluster models
Theories
No-core shell model
Quantum MC
Pieper&Wiringa 05 (AV18+IL2)
Test

24. 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
RIA ?
Test

25. Neutron-rich ions for free – 252Cf spontaneous fission
1 Ci 252Cf source
about 20% of total activity extracted as ions
works for all species
large improvement over existing ISOL based facilities
r-process path
Test

26. CARIBU – new building under construction
Courtesy: R. Pardo
Test

27. CARIBU: RFQ cooler ECR Charge breeder Gas cell 252Cf source Test
Courtesy: R. Pardo
Test

28. Yields for Representative Species
Calculated maximum beam intensities for a 1 Ci 252Cf fission source using expected efficiencies.
Isotope
Half-life (s)
Low-Energy Beam
Yield (s-1)
Accelerated Beam
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

29. 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
RIA ?
Test

30. Solenoidal spectrometer A new concept for studying light-ion reactions
Measured quantities
Flight time: Tflight=Tcyc
Position: z
Energy: Elab
Strong MRI magnet
Heavy-Ion
Derived quantities
Part. ID: m/q
Energy: Ecm
Angle: qcm
p,d,t,3He,a
Inverse kinematics
Field: 5 Tesla
Particle
Tcyc (ns) p
13.1
d,a
26.2 t
39.3
3He
19.7
- Emphasize that this is a new concept
- almost 4pi acceptance
- Automatic particle ID - using ATLAS timing structure
- Simple relation between measured and desired parameters
Test

31. p(44Ti,p’)44Ti kinematics Simulation Simulation q=60o DElab=50 keV10 8 6 4 2
q=60o
DElab=50 keV
Dq=1 deg
Ep (MeV)
qp (degrees) 10 8 6 4 2
DElab=50 keV
Dz=1 mm
DTflight=1 ns
z=25 cm
Ep (MeV)
- two valued kinematic curves in theta, E space
- single valued curves in z, E space in solenoidal field
- much improved Q-value spectra with solenoid
zp (cm)
Test

32. Acceptance F-acceptance: ~100% (q,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 the
acceptance is shown here.
The lower energy cut-off
arises from the outer diam.
of the Si detector and its
proximity to the target (5cm)
Acceptance can be optimized
to specific reaction by moving
target and Si detectors along
beam axis
- Phi acceptance ~100%
- Upper Energy limited by strength and size (length, diam) of magnetic field.
- Lower energy limited by proximity of Si detector to target and beam axis.
Test

33. 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
- Self explanatory
Test

34. 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, a, 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
- self explanatory
Test

35. 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

36. Isotope Shift dn = dnMS + dnFS
Atomic Isotope Shift
Gordon Drake, High precision theory of atomic helium, Phys. Scripta T83: 83 (1999)
Isotope Shift dn = dnMS + dnFS
dnMS 
Mass shift:
due to nucleus recoil
Field shift:
due to nucleus size
FS
 Z  D[(0)]2  <r2> e- e- e-
Measured Calculated Measured Derived
IS(23S1 - 33P2) = 43, (16) (<r2>He4 - <r2>He6) MHz
---- G. W. F. Drake, Nucl. Phys. A737c, 25 (2004)
Test

37. 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 windows
Si-detectors: 12 pos. sensitive Si detectors 1x10 cm
Recoil detectors: DE-E Si array for A<20 recoils
Ionization chamber for heavier recoils
Target wheel/cell
Solenoid
Si-detector array
Vacuum chamber
- homogeneous magnetic 5 tesla field alon g beam axis
- target cell/wheel can be moved along beam axis
- hollow, position sensitive Si-detector array can be moved along beam axis
- detectors in forward angle to catch recoils - coincidences with light charged particles
Test

38. (d,p) Angular Distributions
2H(8Li,p)9Li DWBA calculations,
QMC predictions, no normalization
2H(6He,p)7Heg.s. DWBA calculations
QMC calculations
Optical-model parameters from Schiffer et al, PRC 164
Test

39. Nuclear Astrophysics with Radioactive Beams:
21Na(p,a)18Ne
15O(a,g)19Ne
17F(p,a)14O
56Ni(p,g)57Cu
PRL 82, 3964(1999)
PRC 65, (2002)
PRC 67, (2003)
PRC 67, (2003)
neutron-star
PRL 80, 676(1998)
novae
11C(p,a)8B
Supermassive stars
NPA 734, 615(2004)
8B(b+,n) 2a
12C(a,g)16O
sun
massive stars
supernovae
44Ti(a,p)47V
PRL 84, 1651(2000)
PRL 91, (2003)
Test

40. Energy Level Fits
8He+2n
+2n
6He+2n
S. Pieper and R. Wiringa
Test