The Radioactive Beam Program at Argonne

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

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 ?

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

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.)

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

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

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

8. RIA beams – delayed ‘til 2011 (Bodman)

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.)

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

11. 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

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)

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

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

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) • 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

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 ~ 10-50 counts/hour

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

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. 6He 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). 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

21. Experimental Setup - Schematic ATLAS 12C(7Li,6He)13N 7Li3+: 100 pnA, 60 MeV 2S-2P, 1083 nm 2S-3P, 389 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

22. Single AtomSpectroscopy 4He 6He ~ 150 6He atoms in one hour April 6, 2004

23. A Proving Ground for Nuclear Structure Theories First model-independent determination Pieper&Wiringa 05 (AV18+IL2) L.-B. Wang et al., Phys. Rev. Lett. 93, 142501 (2004) (Nucl-ex/0408008) Reaction collision Experiments Elastic collision Atomic isotope shift Cluster models Theories No-core shell model Quantum MC

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 ?

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

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

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

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

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 ?

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

31. p(44Ti,p’)44Ti kinematics Simulation Simulation 10 8 6 4 2 0 q=60o DElab=50 keV Dq=1 deg Ep (MeV) 30 40 50 60 70 80 90 qp (degrees) 10 8 6 4 2 0 DElab=50 keV Dz=1 mm DTflight=1 ns z=25 cm Ep (MeV) 0 10 20 30 40 50 zp (cm)

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

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

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

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 http://www7.nationalacademies.org/bpa/RISAC_Presentations.html

36. Mass shift: due to nucleus recoil Field shift: due to nucleus size FS  Z  D[(0)]2  <r2> dnMS  Atomic Isotope Shift Gordon Drake, High precision theory of atomic helium, Phys. Scripta T83: 83 (1999) Isotope Shiftdn = dnMS+ dnFS e- e- e- 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)

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

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

39. Nuclear Astrophysics with Radioactive Beams: 56Ni(p,g)57Cu 21Na(p,a)18Ne 15O(a,g)19Ne 17F(p,a)14O PRL 82, 3964(1999) PRC 65, 035803(2002) PRC 67, 065808(2003) PRC 67, 065809(2003) neutron-star PRL 80, 676(1998) novae 11C(p,a)8B Supermassivestars NPA 734, 615(2004) 8B(b+,n) 2a 12C(a,g)16O sun supernovae massivestars 44Ti(a,p)47V PRL 84, 1651(2000) PRL 91, 252501(2003)

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