ATLAS Users Workshop August 8-9 2009 CARIBU: early science program

1. ATLAS Users WorkshopAugust 8-9 2009CARIBU: early science program Guy Savard Argonne National Laboratory and University of Chicago

2. Outline • CARIBU yield curve versus time • It is all about the sources • CARIBU early physics program • Low-energy • Mass measurements • Decay studies • Reaccelerated beams • Coulomb excitation • Single nucleon transfer reactions • Scheduling

3. ATLAS physics program evolution • The ATLAS research program is aligned to the current low-energy nuclear physics priorities • nuclear structure of exotic nuclei • gamma-ray spectroscopy (mostly n-deficient but some light n-rich) • the structure of the heaviest elements • detailed structure of the lightest nuclei by transfer reactions • Astrophysics • nuclear reactions with light radioactive beams (mostly CNO breakout) • masses of exotic nuclei (rp-, np- and r- processes) • Fundamental interactions • CKM unitarity, search for non-standard currents in weak interaction • An emerging interest for both nuclear structure and nuclear astrophysics is moving towards the neutron-rich region (shell-structure modification, r-process) • CARIBU provides ATLAS with new isotopes that can address these evolving priorities of the field

4. Yields for Representative n-rich species versus time • Expected 252Cf fission source strength: • 2.5 mCiend of summer 2009 • 80 mCifall 2009 • 1 Ci source early 2010

5. Early physics program • Once in full production mode, the experimental program will be determined by the PAC … we are here just putting down informed guesses as to what would make the most sense early on with reduced intensities. • Even at reduced intensities in the first half year, CARIBU will provide unique physics possibilities • Low-energy • Mass measurements • Decay studies • Reaccelerated beams • Coulomb excitation • Single nucleon transfer reactions • This early physics program will also be a learning period on the machine and experimental sides.

6. Fission recycling Astrophysics: the r-process path r-process: • Process known to exist • Exact site unknown • Path critically depends on nuclear properties of neutron-rich nuclei: • mass • lifetime • b-delayed neutrons • fissionability Efficient techniques exist to obtain this information but the required beams are missing in most of this region of the chart of nuclides.

7. CARIBU (1 Ci source) Extracted Fission Product Yield New CPT/Old CPTMeasurements New CPT/Old CPTMeasurements Mass measurements on neutron-rich isotopes • Continuation of CPT program • Greatly benefits from even the weakest CARIBU source • Requires > 0.1 ion/s • All marked nuclei accessible with 80 mCi source • All but about half of the grey nuclei are accessible with 2.5 mCi source • CPT moved to CARIBU for about 1.5 years to take advantage of these opportunities

8. CARIBU Moving the CPT to CARIBU CPT tower, electronics and superconducting magnet in final position at CARIBU: CPT tower moved into CARIBU experimental area at the end of July:

9. Initial focus of measurements with the CPT at CARIBU • First measurements: • 132Sn and neighbors • 130Cd and neighbors • Future measurements: • go as neutron-rich as possible … on r-process path

10. Tape station for decay spectroscopy, beam diagnostics, … existing tape station • Tape station for beam diagnostics • beta counter • simple gamma detection system • Tape station for decay spectroscopy • detector systems • X-array • Total absorption spectrometer • Neutron detectors • 4p beta counter • research topics • nuclear spectroscopy • r-process • decay heat and other applications new tape stations under construction and X-array

11. diagnostics tape station laser table ion trap CPT CARIBU low-energy area experimental equipment decay tape station CPT

12. GSFMA 155 (February 2005)Background subtracted, Doppler corrected spectrum 138Ce@480MeV

13. How much beam do we need with Gammasphere? 14h at 6.109pps! 1/25 107 pps for 2 weeks 1/250 106 pps for 2 weeks • To get B(E2) of first 2+ state, we need ≥102 pps • To identify excited 2+ state (beyond the 2+1) in vibrational nucleus (B(E2)~1Wu) with Gammasphere for 2 weeks beam time we need ~105 pps. • For complete spectroscopy, 106-107 pps is needed 1/2500 105 pps for 2 weeks

14. How Octupole collective are neutron rich barium nuclei? This has been an open question for 20 years. Fission fragment spectroscopy and b-decay have found parity-doublet bands of states. But almost NO data on real matrix elements, either quadrupole or octupole. Octupole correlations only from E1/E2 ratios Key Study: Coulomb excitation of 144,146Ba On Lead target at ~750MeV for multi-step. On Carbon target at ~630MeV for non-yrast. Measure B(E1), B(E2), B(E3) GS Photopeak yield with 104pps ~ 70 cts/hr Leander at al PL 152B (1985)

15. Requirements of n-rich physics: Nucleon transfer reaction … single particle state • Single particle/hole states around magic nuclei • 132Sn, 104Zr, 78Ni • (d,p) reactions • best done well above Coulomb barrier in both entrance and exit channels … i.e. about 7.5 MeV/u around 132Sn • requires 104 per second to get information on angular distribution • (3He, a), (a,t) reactions • Well matched to higher angular momentum transfer • Energy requirements again set by Coulomb barrier … want ~ 11 MeV/u • Required beams are not available anywhere at present • The Helios spectrometer, together with the beam energies available with the ATLAS upgrade, provides ideal conditions for these experiments.

16. CARIBU Reach Evolution of shell gaps in neutron-rich nuclei

17. Single-neutron transfer on N=82: CARIBU➝ATLAS➝HELIOS • d(134Te,p)135Te @ 8 MeV/u • Q value = 1.115 MeV, B = 2T • Clearly identify low-ℓ transfer (1,3) from angular distributions • Isobaric contaminants low (factor 10 lower), recoil detector not crucial • Expect ~1×104134Te per second on 200 μgcm–2 CD2 target with (d,p) cross sections of ~1-15 mb/sr • Current array ~50% ‘dead’ area, however, ~6 days beam should yield >1000 cts per state. • With 80 mCi and for accelerated beam expect ~ 1×104134Te per second • Using a 200 μgcm–2 CD2 target • Current prototype silicon array has ~ 50% of π • Cross sections between ~1-15 mb/sr • Expect ~0.05 counts per min per state (@ 10 mb/sr) • This depends on how much we want? 1000 counts, this would be tough! • With 80 mCi and for accelerated beam expect ~ 1×104134Te per second • Using a 200 μgcm–2 CD2 target • Current prototype silicon array has ~ 50% of π • Cross sections between ~1-15 mb/sr • Expect ~0.05 counts per min per state (@ 10 mb/sr) • This depends on how much we want? 1000 counts, this would be tough!

18. Scheduling constraints • CARIBU will use 3 different degrader foil thicknesses to cover the full range of fission fragments • one degrader to cover the light fission peak, two degraders to cover the heavy fission peak • System is designed so that the degraders can be changed locally without going back to the hot cells • Initial commissioning of CARIBU will be performed with a 143Ba beam … hence a degrader tuned for this mass range • These beams will be used to “debug” CARIBU, this might take some time, and hence the first series of CARIBU experiments must concentrate on this mass range • Next degrader will be tuned for the light masses and experiments will concentrate around the Mo and Zr region which are particularly interesting for nuclear structure physics.

19. CARIBU beamtime scheduling • The PAC will accept proposals for CARIBU beams once we have gained sufficient understanding of what beams will be available, at what intensity, with what properties, and how well they can be used in the different experimental setups • Until then, CARIBU beamtime will be used to determine the real capabilities of the new facility, emphasizing: • determining the yields at low energy and with reaccelerated beams … with some measurements on both the heavy and light fission peaks • commissioning beam diagnostics and accelerator tuning • learning how to use the various experimental setups with these beams • This development period is expected to last until the end of the year and during this period the physics that can be performed simultaneously with the development runs will be opened to all collaboration members

21. Single-neutron transfer on N=82: CARIBU➝ATLAS➝HELIOS 144Sm stable • Key nuclear structure: energies (and character) of single-particle states in these nuclei are essential information for nuclear structure models. • The N=82 isotones allow us to track the evolution of single-particle energies over a large range of neutron excess. • Data limited to only the stable N=82 isotones. • CARIBU provides intense beams for the 50≤Z≤54 – so far no definitive data for these. • HELIOS, with prototype detectors, capable of these measurements 143Pm 142Nd stable • Low-lying states thoroughly studied • (d,p) low-ℓ transfer • (α,3He) high-ℓ transfer • Recent interest in the evolution of h9/2 and i13/2 orbitals 141Pr stable 140Ce stable 139La stable 138Ba stable (A-Z) increases • Gas-cell target (d,p), poor resolution • GSI, 1991, did reaction in inverse kinematics • ORNL, 2005, 13C(136Xe,12C) γ, γ correlations 137Cs >106 136Xe stable 135I >106 • 13C(134Te,12C) g-g correlations • ORNL, 2007, d(134Te,p) • Do (d,p) at optimum beam energy now 134Te >106 133Sb >106 132Sn 105-106 (Near) future CARIBU beam Z=50 N=82

22. Preparation for mass measurements at CARIBU Deceleration optics • Site preparation ongoing • Need to turn CW 50 keV beam into 3 keV bunched beam for highest efficiency • RFQ buncher under construction within CPT collaboration • Beamline optics calculations completed • CPT was turned off at ATLAS in July and main components have been moved to CARIBU • CPT reassembly at CARIBU should be completed in September “Elevator” RFQ buncher to CARIBU low-energy area

23. Do neutron rich barium nuclei show X(5) symmetry? Analytic model for nuclei at critical point of transition from spherical to deformed shapes Provides good description of N = 90 isotones of Nd, Sm, and Gd Key signatures involve low-spin, non-yrast states Lighter Z, N=90 nuclei seem to have similar structure BUT essential states are not known Key Study: Beta decay into 146,148Ce Measure: Non-yrast state energies and branching ratios