ATLAS Users Workshop August CARIBU: early science program Guy Savard Argonne National Laboratory and University of Chicago

G. Savard 2009 ATLAS Users Workshop August 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

G. Savard 2009 ATLAS Users Workshop August 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-, p- 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

G. Savard 2009 ATLAS Users Workshop August Yields for Representative n-rich species versus time Expected 252 Cf fission source strength: 2.5 mCiend of summer mCifall Ci source early 2010 IsotopeHalf-life (s) Low-Energy Beam Yield (s -1 ) Accelerated Beam Yield (s -1 ) 104 Zr1.21.5x10 3 / 4.8x10 4 / 6.0x x10 1 / 1.7x10 3 / 2.1x Ba x10 4 / 9.6x10 5 / 1.2x x10 3 / 3.4x10 4 / 4.3x Ba4.01.4x10 4 / 4.4x10 5 / 5.5x x10 2 / 1.6x10 4 / 2.0x Sn x10 3 / 7.8x10 4 / 9.8x x10 1 / 2.9x10 3 / 3.6x Sn40.9.3x10 2 / 3.0x10 4 / 3.7x x10 1 / 1.1x10 3 / 1.4x Xe x10 4 / 7.8x10 5 / 9.8x x10 3 / 5.8x10 4 / 7.2x Mo2.81.6x10 2 / 5.0x10 3 / 6.2x x10 0 / 1.8x10 2 / 2.3x Mo0.58.3x10 0 / 2.6x10 2 / 3.3x x10 0 / 9.6x10 0 / 1.2x10 2

G. Savard 2009 ATLAS Users Workshop August 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.

G. Savard 2009 ATLAS Users Workshop August 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  -delayed neutrons -fissionability Fission recycling Efficient techniques exist to obtain this information but the required beams are missing in most of this region of the chart of nuclides.

G. Savard 2009 ATLAS Users Workshop August 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 New CPT/ Old CPT Measurements CARIBU (1 Ci source) Extracted Fission Product Yield

G. Savard 2009 ATLAS Users Workshop August CARIBU Moving the CPT to CARIBU CPT tower moved into CARIBU experimental area at the end of July: CPT tower, electronics and superconducting magnet in final position at CARIBU:

G. Savard 2009 ATLAS Users Workshop August Initial focus of measurements with the CPT at CARIBU First measurements: 132 Sn and neighbors 130 Cd and neighbors Future measurements: go as neutron-rich as possible … on r-process path

G. Savard 2009 ATLAS Users Workshop August Tape station for decay spectroscopy, beam diagnostics, … 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 4  beta counter –research topics nuclear spectroscopy r-process decay heat and other applications existing tape station new tape stations under construction and X-array

G. Savard 2009 ATLAS Users Workshop August CARIBU low-energy area experimental equipment diagnostics tape station decay tape station CPT laser table ion trap

G. Savard 2009 ATLAS Users Workshop August GSFMA 155 (February 2005) Background subtracted, Doppler corrected spectrum 138

G. Savard 2009 ATLAS Users Workshop August How much beam do we need with Gammasphere? 14h at pps ! 1/25 1/250 1/ pps for 2 weeks 10 6 pps for 2 weeks 10 5 pps for 2 weeks To get B(E2) of first 2+ state, we need ≥ 10 2 pps To identify excited 2 + state (beyond the ) in vibrational nucleus (B(E2)~1Wu) with Gammasphere for 2 weeks beam time we need ~10 5 pps. For complete spectroscopy, pps is needed

G. Savard 2009 ATLAS Users Workshop August How Octupole collective are neutron rich barium nuclei? This has been an open question for 20 years. Fission fragment spectroscopy and  -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 144,146 Ba 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 10 4 pps ~ 70 cts/hr Leander at al PL 152B (1985)

G. Savard 2009 ATLAS Users Workshop August Requirements of n-rich physics: Nucleon transfer reaction … single particle state Single particle/hole states around magic nuclei 132 Sn, 104 Zr, 78 Ni (d,p) reactions –best done well above Coulomb barrier in both entrance and exit channels … i.e. about 7.5 MeV/u around 132 Sn –requires 10 4 per second to get information on angular distribution ( 3 He,  ), ( ,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.

G. Savard 2009 ATLAS Users Workshop August Evolution of shell gaps in neutron-rich nuclei CARIBU Reach

G. Savard 2009 ATLAS Users Workshop August Single-neutron transfer on N=82: CARIBU ➝ ATLAS ➝ HELIOS With 80 mCi and for accelerated beam expect ~ 1× Te per second Using a 200 μgcm –2 CD 2 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× Te per second Using a 200 μgcm –2 CD 2 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! d( 134 Te,p) MeV/u Q value = 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× Te per second on 200 μgcm –2 CD 2 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.

G. Savard 2009 ATLAS Users Workshop August 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 143 Ba 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.

G. Savard 2009 ATLAS Users Workshop August 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

G. Savard 2009 ATLAS Users Workshop August

G. Savard 2009 ATLAS Users Workshop August Single-neutron transfer on N=82: CARIBU ➝ ATLAS ➝ HELIOS 144 Sm stable 143 Pm 142 Nd stable 141 Pr stable 140 Ce stable 139 La stable 138 Ba stable 137 Cs > Xe stable 135 I > Te > Sb > Sn N=82 Z=50 (A-Z) increases 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 Low-lying states thoroughly studied (d,p) low-ℓ transfer (α, 3 He) high-ℓ transfer Recent interest in the evolution of h 9/2 and i 13/2 orbitals Gas-cell target (d,p), poor resolution GSI, 1991, did reaction in inverse kinematics ORNL, 2005, 13 C( 136 Xe, 12 C) γ, γ correlations (Near) future CARIBU beam 13 C( 134 Te, 12 C)  correlations ORNL, 2007, d( 134 Te,p) Do (d,p) at optimum beam energy now

G. Savard 2009 ATLAS Users Workshop August Preparation for mass measurements at CARIBU 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 Deceleration optics RFQ buncher “Elevator” to CARIBU low-energy area

G. Savard 2009 ATLAS Users Workshop August 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 146,148 Ce Measure: Non-yrast state energies and branching ratios