Rare Isotope Accelerator Facilities of North America 18th Winter Workshop on Nuclear Dynamics Nassau, Bahamas January 23, 2002 J. Nolen, ANL
The Limits of Nuclear Stability Heavy Elements Fission Limit? Known Nuclei Proton Drip Line Stable Nuclei Neutron Drip Line? Thomas Glasmacher
Outline • Present Radioactive Beam Facilities of North America • Some current science examples • From NSCL, ISAC, HRIBF, & ATLAS • The Proposed RIA Facility • Overview • Science Opportunities • The Technologies • Summary
Exotic beams via projectile fragmentation • Physical means of separation: short development times • Highly selective separation (1 in 1016 - 1018) • Secondary beam is fast (v/c = 0.3- 0.6) • Facilities in operation at GANIL (France), GSI (Germany), NSCL (USA), RIKEN (Japan)
Projectile fragmentation at the NSCL K500cyclotron A1900 fragment separator K1200cyclotron
Determination of Spectroscopic Factors from Knock Out Reactions • Spectroscopic factors are determined from the population of excited states in the A-1 fragment. • The l-value of the removed nucleon is determined from the recoil momentum distribution of the fragment.
Example:17C(3/2+) 16C+g l=2 4411 mb Theo. 53 mb l=0 167 mb Theo. 12 mb V. Maddalena et al., Phys. Rev. C 63 (2001) 024613
Example: Structure of 12Be 9Be(12Be,11Be*) at 78 MeV/u with γ-ray coincidences. Not observed 5/2+ ½- 12Be ½+ 11Be Navin et al. accepted PRL 2000
Coulomb Excitation of Exotic Beams In-flight at NSCL Experiments can be performed with as low as 0.1 ions/s with beam energies of 50-150 MeV/u Thomas Glasmacher
Intermediate Energy Coulomb Excitation to Study Structure of Exotic Nuclei • Excite neutron-rich secondary beam particle in heavy target (e.g. gold) and detect de-excitation photon • Measure the energy of first excited state E(2+) and extract B(E2,g.s. 2+) for exotic nuclei • Method works at peak of exotic beam production cross-section for projectile fragmentation (50-100 MeV/nucl.) with beam rates of 1/s • Schematic setup: Thomas Glasmacher/NSCL
(Coulomb excitation with fission fragments) David Radford, ORNL
Measuring the Charge Radii of 6He and 8He • Motivation • Test the Standard Model of Nuclear Structure; • Study nucleon interactions in neutron-rich matter. Standard Model of Nuclear Structure 6He Neutron Star
Production of Thermal and Neutral 6He Atoms September, 2001 ATLAS Reaction: 12C(7Li, 6He)13N 7Li beam @ 20 pnA, 6He atoms extracted at 3 ´ 105 /s Lu, Rehm, et al., ANL
This experiment requires a precision beam for implantation in a thin Si detetector
Why is RIA Unique and New? • 10-100x stronger uranium beams • Used with fast gas catcher to enable precision beams of reaccelerated rare isotopes without chemical dependence • World’s highest intensity in-flight facility • 8x stronger light ion beams • All species, e.g. 0.9-GeV protons, 2-GeV 3He
Partial Beam list for the RIA Driver Linac 400 kW beam power
NSAC RIA Costing Subcommittee Report M. Harrison, Chair, et al. : Report to NSAC Jan. 2001 • RIA Total Project Costs: 834M$ • TEC 644M$ (695M$ without cost savings) “The TEC as presented is reasonable…We did not find any significant omissions from the TEC costs” • 94M$ allotted for experimental equipment (included in the TEC) • R&D 25M$ - “appear somewhat low” (40M$) • Pre-CDR, CDR and NEPA 15M$ • Pre-Ops 150M$ - “appear somewhat high” (135M$) • “We find the design is essentially stable and recent changes have involved scope” • Operating budget of 75M$/y is reasonable.
The Scientific Case for Rare Isotope Beams • The origin of the elements – Quantitative understanding of astrophysical processes. RIBs are the only methods to produce and study the isotopes critical to the energy generation and nuclear synthesis in stars. • The limits of nuclear stability – What combinations of neutrons and protons can make up a nucleus? • Properties of nuclei with extreme neutron to proton ratios – an extreme challenge to many-body theories. • Properties of bulk neutron matter and the nature of neutron stars – Study of neutron star material and the neutron matter equation of state. • Quantum Mechanics of Mesoscopic Systems – How are complex systems organized from simple building blocks. What is the Hamiltonian for many body theory that describes the nucleus? How can this be derived from fundamental interactions? • Tests of Fundamental Interactions – Nuclei serve as a laboratory for fundamental studies: CKM matrix, annapole moment, PNC, electric dipole moment.
What scientific questions will RIA answer? • Origin of the elements and energy generation in the cosmos by nuclear processes • Supernovae science (requires nuclear science input) • The nature of neutron stars (x-ray bursts, crust and bulk properties) • Nature of nucleonic matter • What combinations of neutrons and protons can make up a nucleus? • What is the appropriate, comprehensive model for nuclei and how do we understand it in terms of nucleon-nucleon interactions and ultimately in terms of the strong interaction? • Can we understand the nature of unusual forms of nuclear matter (halos,skins)? • What is the isospin dependence of the nuclear matter equation of state?
What scientific questions will RIA answer? • Tests of the standard model • What is the nature of CP violation? The best probe of flavor-conserving CP violation is in the measurement of an atomic EDM. Radon isotopes provide good cases for these studies. • RIA will exploit the larger Parity Violation in Francium isotopes to search for physics beyond the Standard Model. • Are there weak interactions beyond V-A? • RIA may help improve the precision of the measurement of Vud in order to test the unitarity of the CKM Matrix.
Sample Experiments at RIA • Limits of nuclear stability • Nuclide identification (1/week) • Fission mass surface (1000/s) • Super-heavy Elements (>109/s for mid-mass nuclei) • Nuclear bench marks (Magic Nuclei) • 132Sn (109/s) • 48,78Ni, 100Sn (>.01/s) • r-process nuclides • Half-lives (1/d) • Masses (>100/d) • Evolution of structure with isospin (neutron skin) • Single step Coulomb excitation, Knockout (>0.01/s) • Multi-step Coulomb excitation (>100/s) • Nucleon transfer (>103/s) • Halo Nuclei • Wave functions (>0.01/s) • Tests of the standard model • Rn (>109) • Fr (>109)
Advantages of ISOL/Reaccelerated Beams • Stopped and cooled beams for trap measurements (e.g., Rn and Fr) • High quality beams at or near the Coulomb barrier • Low energy reactions mechanisms • Fusion/Evaporation • Near barrier transfer • Proton and neutron stripping reactions for the study of single particle and multi-particle states • Coulomb excitation (multiple excitations to study higher lying states) • Direct measurement of resonant and direct capture reactions • Experimental considerations • Thin targets ( 100 mg/cm2) • Isobar separation is required • Reaccelerated beam experiments can work with 103 ions/s or more (ANL,ND,TAM)
Advantages of Fast Beams • > 50MeV/u without reaccelerating • High energy reactions mechanisms • Eikonal methods for direct reactions • Giant Resonance excitation • Single-Step Coulomb excitation (E1/M1/E2) • EOS studies (flow, balance energy) • Charge exchange • High sensitivity • Thick targets (g/cm2 vs. mg/cm2) and 1000-10,000 gain in luminosity • Relatively easy identification of single ions (A,Z identification) • Ability to work with atoms/week (48Ni GANIL, 100Sn GSI/GANIL) • Extend the scientific reach to 4-5 mass units farther from stability
Weakening of Shell Structure in Exotic Nuclei PROTON NUMBER 68 62 56 50 44 38 N=80 24 N=82 ) N=84 20 V N=86 e e e 16 e n e n n i n M i l i l i l l p p p ( i p i 12 r i r i r d r d d d n n n n 2 o n o o 8 r S o r t t t t o u o u r e r e p n p n 4 0 1.2 1.5 1.8 2.1 2.4 N / Z J. Dobaczewski and W. Nazarewicz Phil. Trans. R. Soc. Lond. A 356, 2007 (1998) present RIA .01/s limit
Nuclei with extended wave functions • Efimov states: Mazumdar et al. PRC 61 (2000) 051303; V. Efimov, Phys. Lett. B 33 (1970) 563 • Pairing and closeness of the continuum: Esbensen and Bertsch, Phys. Rev. C 91, Dobaczewski et al. Phys. Rev. Lett 72 (1994) 981; Meng and Ring PRL 80 (1998) 460
Neutron halo in 42Mg Sn = 100 keV HF-Skyrme interaction tuned for ground state properties B.A. Brown, Phys. Rev. C 58 (1998) 220
Tests of Fundamental Conservation Laws Examples: • Atomic Electric Dipole Moments • Parity Violation • Beyond V-A • Unitarity of the CKM Matrix New tools offer new opportunities and clever experimenters will take advantage of them.
Atomic Electric Dipole Moments • The observed Baryon density of the Universe implies CP violation. • One of the best probes for CP violation in flavor conserving interactions is the measurement of a permanent electric dipole moments of atoms or neutrons. Present limits are about an order of magnitude below predicted levels. • Octupole deformation enhances the Schiff moment by 100x. The nuclide 223Rn would be an excellent case to study. • RIA would provide the highest intensity of 223Rn (by 100 to 1000 times other facilities).
Parity Violation using Francium Isotopes • Measurements of atomic parity violation are sensitive to new physics beyond the Standard Model. • Recent experiments in Cs have hinted at the need for extra gauge bosons (the conclusion depends on atomic corrections). • Experiments with Fr will provide a more sensitive probe of weak charge since parity violation scales with Z3. The violation can also be studied over a wide range of neutron number to help eliminate nuclear effects. • RIA will provide sufficient intensity to study 20 isotopes of Francium.
Important Technical Features of RIA ·High power CW SC Linac Driver (1.4 GV, 400 kW) Advdanced ECR Ion Source Accelerate 2 charge states of U from ECR All beams: protons-uranium Superconducting over extended velocity range: 0.2 – 900 MeV/u Multiple-charge-state acceleration after strippers Adapted design to use both SNS cryomodules RF switching to multiple targets ·Large acceptance fragment separators 1) “Range Bunching” + Fast gas catcher for ISOL 2) High resolution and high purity for in-flight ·High power density ISOL and fragmentation targets Liquid lithium as target for fragmentation and cooling for n-generator ·Efficient post-acceleration from 1+ ion sources ·Next-generation instrumentation for research with rare isotopes
RIA involves many novel technical concepts, but they are under control and do not involve significant risk.
A key capability is multi-charge state acceleration Uranium Acceleration Scheme 10 MeV/u85 MeV/u 400 MeV/u Calculated multiple charge state acceleration in the high E section: 1st stripper q = 69-73 2nd stripper q = 87-90 ECR q=28,29 Calculated multiple charge state injection:
Target Areas and Beam Sharing Two independent radioactive beam and one stable beam experiment can be run concurrently.
Fast-Gas Catcher • One of the major problems with the standard ISOL production target design was the sensitivity of the process to the chemistry of the produced ions. • With the fast-gas-catcher the ions are stopped in helium gas, where they remain ionized with high efficiency, the ions can be extracted with electromagnetic techniques. The result: an entirely new paradigm for producing rare isotopes. Working prototype in use at ANL • ANL-GSI-MSU-RIKEN Collaboration to test at full energy.