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Transfer reactions with exotic beams at ATLAS: Current status and future prospects

This presentation discusses the current status and future prospects of transfer reactions with exotic beams at ATLAS. It covers topics such as the importance of light nuclei for nucleosynthesis, laboratories for testing modern nuclear structure methods, and the experimental setup used for (d,p) and (d,3He) reactions.

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Transfer reactions with exotic beams at ATLAS: Current status and future prospects

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  1. Transfer reactions with exotic beams at ATLAS Current status and future prospects A. H. Wuosmaa

  2. Why Light Nuclei? • Laboratories for testing modern “ab-initio” nuclear structure methods (Quantum Monte Carlo, No-Core Shell Model) • Beyond bound (or narrow) states – QMC, continuum shell model calculations for resonances. • Importance of light nuclei for nucleo-synthesis – Big-Bang Nucleo-synthesis, “non-standard” r-process Today – focus on (d,p) and (d,3He) reactions

  3. Producing unstable beams Re/De-bunching resonator “In-flight” production at ANL* Gas cell:H2 or D2 1.4 Atm. Focusing solenoid Magnetic separator Primary Primary and secondary Primary and secondary Primary Primary beam 1 X 1011 particles/sec RF Beam sweeper Secondary *B. Harss, K. E. Rehm et al., Rev. Sci. Instrum. 71, 380 (2000)

  4. Some recently used beams from ATLAS

  5. (d,p) Experimental setup Monitor EDE telescope Au Monitor target proton CD2 target Beam axis recoil Forward-angle EDE detectors qlab=1o-7o Annular silicon detectors Wlab ~ 3.5 sr qlab=109o-159o

  6. (d,3He) Experimental setup Monitor EDE telescope Au Monitor target 3He CD2 target Beam axis recoil Forward-angle EDE detectors qlab=1o-7o Annular silicon detectors Wlab ~ 2.2 sr qlab=9o-50o Our secondary-beam intensities are ~1-10X104 particles/sec Event rate for 10 mb/sr ~ 10-100 counts/hour

  7. Detectors Segmented proton detectors 500mm/1000mm silicon EDE telescope

  8. Q-value spectrafrom (d,p) p-Li or p-6He coincidences Efficiency from Monte Carlo simulations PRL 94, 082502 (2005), PRC 72, 061301(R) (2005)

  9. (d,p) Angular Distributions - narrow states 2H(8Li,p)9Li DWBA calculations: Red, blue curves: QMC predictions with different OMP, no extra normalization 2H(6He,p)7Heg.s. DWBA calculations QMC calculations. Blue: no normalization violet- QMC X 0.69. Optical-model parameters from Schiffer et al, PRC 164

  10. Hypothetical spectrum of 7He Overlapping resonances – who is who? Quantum Monte Carlo S. C. Pieper et al. PRC 70, 2004 How can we distinguish different excitations? Use selective reactions!

  11. 7He – Spectroscopic Factors 6He(0+): particle stable 6He(2+): decays to 4He+2n PRC 72, 061301 (2005), R. B. Wiringa Priv. Comm Quantum Monte Carlo, No-Core Shell Model

  12. Comparisons for 7He CD2 CD2-12C 1/2-?? 5/2-?? PRC 72, 061301 (2005)

  13. d(8Li,3He)7He angular distributions Green- QMC+PTOLEMY scaled Blue, Violet – DWBA scaled, two different potentials Absolute DWBA predictions are extremely sensitive to 3He exit channel parameters, but relative predictions are not. -- DWBA: Open question --

  14. Preliminary results for d(12B,p)13B Red Lines: DWBA calculations 2H(11B,p)12B data scaled to calculation 0.95;2+ 2H(11B,p)12B 0.0;1+ 1.67;2- 3.39;3- 2.62;1- 2.72;0+ 2H(12B,p)13B Shell model: Sn(13Bg.s.)=0.78 (B. A. Brown, priv. comm.) 0.0; 3/2- Expected positive-parity states 3.48, 3.68 5.02

  15. HELIcal Orbit Spectrometer(HELIOS) Recoil detector Conceptual design Target Downstream Si array Upstream Si array Beam axis Solenoid TOF = 1 cyclotron period Dispersion in parallel velocity NIM A 580, 590 (2007)

  16. Realistic Simulations: d(132Sn,p)133Sn DE=50 keV Dq=1o “kinematic compression” DE=50 keV DZ=1 mm Improved resolution for (d,p) – similar for other reactions

  17. Solenoid End flange Spool Solenoid bore as vacuum chamber Si array Beam Target Target mechanism First generation spectrometerunder construction now 40 element array 2 x 5 cm silicon PSDs S. Heimsath

  18. HELIOS under construction

  19. Conclusions • QMC calculations can make testable predictions for n-transfer spectroscopic factors – but a good understanding of optical model parameters is important for detailed comparisons with data • Theoretical predictions for 7He excited states seem to be vindicated • Current approaches to transfer reactions with exotic beams in inverse kinematics have limitations • New spectrometer – HELIOS – may address complications of current approaches (resolution, particle identification, backgrounds)

  20. Thanks to: Argonne Northwestern University Hebrew University K. E. Rehm J. P. Greene D. J. Henderson R. V. F. Janssens C. L. Jiang H. Y. Lee E. F. Moore R. C. Pardo D. Peterson S. C. Pieper G. Savard J. P. Schiffer S. Sinha X. Tang R. B. Wiringa M. Paul L. Jisonna R. E. Segel KVI CO School of Mines R. H. Siemssen N. Patel Western Michigan University J. Lighthall S. Marley N. Goodman AHW Lots of guidance from theorists!

  21. And - The HELIOS Collaboration J. C. Lighthall, S. T. Marley, J. R. Winkelbauer (SULI student), A. H. Wuosmaa* Western Michigan University B. B. Back**, H. Y. Lee, C. J. Lister, P. Mueller, K.E. Rehm, J. P. Schiffer, K. Teh, A. Vann (SULI student) Argonne National Laboratory S. J. Freeman, B. Kay University of Manchester Work supported by the U. S. Department of Energy, Office of Nuclear Physics, under contract numbers DE-FG02-04ER41320 (WMU) and DE-AC02-06CH11357 (ANL) Also, special thanks to: N. Antler, Z. Grelewicz, S. Heimsath, J. Rohrer, J. Snyder *Spokesperson, **Project Manager

  22. Supplementary Slides

  23. Target thickness effects: “worst case”: d(132Sn,p)133Sn “Conventional” HELIOS “Conventional”: Q-value resolution strongly affected by detector segmentation and target thickness HELIOS: Q-value resolution is affected by target thickness – worst behavior is with heavy beams. With lighter beams HELIOS wins hands down.

  24. HELIOS kinematics Particles are detected at fixed Zlab, so V||=VCM+vcm|| is fixed. v1lab v1cm v2lab v2cm VCM Vcm|| Zlab=(VCM+Vcm||)xTCYC FIXED! !

  25. d(6He,p)7He angular distributions 7He ground state 7He first-excited state? Variational Monte Carlo predictions PRC 72, 061301 (2005)

  26. 2H(6He,p)7He Q-value spectrum EX=2.6 MeV Simulation of 5-body final state: 7He*→6He(2+)+n→ 4He+3n Counts/160 keV 7He*→4He+3n 6He(2+) Branching ratio ~ 0.1 (Th.) 0.2±0.1 (Exp.) Q Value (MeV) p-4He coincidences

  27. p(8He,d)7He A. A. Korshennenikov et al., PRL 82 1999 7He: Various Experiments H. G. Bohlen et al., PRC 64 024312 (2000) p(8He,d)7He F. Skaza et al., PRC 73, (2006) 8He Breakup 1/2-? M. Meister et al., PRL 88 (2002).

  28. 8He(p,d) Particle ID Skaza et al, PRC 73, 2006

  29. 7/2+ 5.50 5.30 5/2+ 5.02 1/2- 4.70 5/2+ 4.13 4.00 3.71 3/2+ 3.90 3.68 3.53 1/2+ 3.48 3.00 3/2- 3/2- 0.0 0.0 Comparison between experiment and shell model From 11B(t,p)13B: p=+: Jp=(1/2+,3/2+,5/2+) p=-: Jp=(1/2-,5/2-,7/2-) study l=0,2 transitions in 12B(d,p)13B Underlined levels populated in (d,p) 13B(Experiment) (t,p): Middleton and Pullen, NP 50, 1964 13B(Shell Model) (B. A. Brown, priv. comm.)

  30. Realistic Simulations: p(44Ti,p’)44Ti* DE=50 keV Dq=1o DE=50 keV DZ=1 mm “Forward Kinematics”

  31. CM angle determination vlab (measured) vcm (from excitation and beam energies) VCM (from beam energy) qcm (light particle) Only directly measured quantity

  32. Prototype Silicon Detector Array Prototype array built from 24 “legacy” 5cm x 1cm detectors Position Sensitivity in z-direction Full 40-Element Array 5cm x 2cm Detectors

  33. Overlaps and (d,p) Spectroscopic factors from VMC <6He(0+)+n(p3/2)|7He(3/2-)> <6He(0+)+n(p1/2)|7He(1/2-)> 3/2- 1/2- R. Wiringa, priv. comm.

  34. Theoretical and experimental spectroscopic factors for 8Lig.s.+n→9Li PRL 94, 082502 (2005)

  35. Neutron spectroscopic factors for 6He(0+)+n, 6He(2+)+n Accessible via (d,p)

  36. Calibrations with 7Li beam 3He-6He 6He(0+) Calibration reactions with various recoils detected at forward angles 6He, 4He, 6Li are identified t-6Li 6Li(1+) 6Li(0+) t,3He-4He 6Li(3+) 6He(2+) (12C subtracted)

  37. d(7Li,t)6Li angular distributions Red – QMC+PTOLEMY unscaled Green- QMC+PTOLEMY scaled Blue line – standard DWBA Violet line- standard DWBA scaled

  38. d(7Li,3He)6He angular distributions Red – QMC+PTOLEMY unscaled Green- QMC+PTOLEMY scaled Blue points – Data from Stokes & Young Blue line – standard DWBA Violet line- standard DWBA scaled Very significant sensitivity to Optical Model parameters!

  39. ? 0d3/2 0d3/2 1s1/2 1s1/2 0d5/2 0d5/2 0p1/2 0p3/2 0p1/2 0p3/2 0s1/2 p n 0s1/2 13B p n Intruder states 13B Study 2H(12B,p)13B Objectives: Determine order of low-lying positive-parity excitations; Determine Sn for g.s. transition – any depletion in Sn(g.s) from (1s1/2)2 components?

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