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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.)

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

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 Test

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

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)

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

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 Test

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

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

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

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

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

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

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

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

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

p(44Ti,p’)44Ti kinematics Simulation Simulation q=60o DElab=50 keV 10 8 6 4 2 q=60o DElab=50 keV Dq=1 deg Ep (MeV) 30 40 50 60 70 80 90 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 0 10 20 30 40 50 zp (cm) Test

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

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

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

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

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) = 43,196.202(16) + 1.008(<r2>He4 - <r2>He6) MHz ---- G. W. F. Drake, Nucl. Phys. A737c, 25 (2004) Test

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

(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

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, 035803(2002) PRC 67, 065808(2003) PRC 67, 065809(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, 252501(2003) Test

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