Nuclear Excitation via Electron Capture NEEC. Realistic Experimental Scenario at a Storage Ring

Transcription

1 Nuclear Excitation via Electron Capture NEEC Realistic Experimental Scenario at a Storage Ring Christophor Kozhuharov GSI Darmstadt Atomic Physics Division Workshop on Nuclear Physics in Hot Dense Plasmas London, March 13 14

2 Overview GSI facilities, experimental opportunities The LLNL-GSI-Jena-Heidelberg-CEA/DAM-Surrey-LoI Internal conversion, Auger Electrons, Time inversed processes: NEEC and DR NEEC Experimental Scenario (NEECX) signature, signal/background, luminosity, resonance strength Summary and Outlook

3 Present GSI Accelerators Heavy Ion Synchrotron,SIS, 2 AGeV for A/q=2 (1 AGeV U) Ion sources Heavy Ion Linac UNILAC (<20 MeV/u) - Beams of all (chemical) elements and all stable isotopes: from hydrogen to uranium - Broad range of energies: from thermal to relativistic energies (2AGeV) - Secondary beams of unstable (radioactive) nuclei; ground state, isomers - Unique beam properties: well-defined charge states, cooled and stored beams - Decelerated and cooled species HITRAP (4 K) - (pions) Fragment Separator FRS Experimental Storage Ring ESR

4 Protonenzahl Z Neutronenzahl N

5 Stochastic cooling at the ESR Long. Kicker Transv. Pick-up Combiner Station Transv. Kicker Long. Pick-up ESR storage ring Stochastic cooling - particularly efficient for hot ion beams Fixed ione trajectory and energy: 400 MeV/u)

6 Cooling, i.e. enhancing the phase space density at constant beam velocities Electron cooling: G. Budker, 1967 Novosibirsk The momentum exchange of the ions with the cold collinear e - beam leads to an excellent emittance

7 'Phase transition' to a linear ion chain ESR circumference 10 4 cm For 1000 stored ions, the mean distance amounts to about 10 cm. At mean distances of about 10 cm and larger the intra-beam-scattering disappears. M. Steck et al., PRL 77, 3803 (1996)

8 Recording the Schottky-noise From the FRS To the SIS Dipole magnet Septummagnet Hexapolemagnets Quadrupoletriplet v 0 v Schottky pick-ups Gas-target Electron cooler Schottky Pick-ups amplification summation FFT Quadrupoledublet f ~ 2 MHz 0 Stored ion beam RF-Accelerating cavity Fast kicker magnet Extraction

9 300 khz / 60 MHz Schottky TCAP W Pt mass unknown Tl Bi Tl Au Po Hg 78+ Pt Hg Bi Ir 186 Au Os Pt Ir Po Bi Au 77+ W 184 Pt 77+ Ir 181 Tl X Pb 81+ Tm68+ Pt Po Ir Os Dy Tb Gd Hf 147 known masses unknown masses Tl Pt q+ q+ Lu 74+ W Er Ho Nd X A Os75+ Au 78+ Bi 83+ Hg Lu 161 Gd I A 198 Tl 80+ Yb 77+ Ir Re W Hg 80+ Pt Hg 80+ Ir Pb Pb Dy Yb Au Bi Re74+ Pr Eu 62+ Sm m,g Bi Pb Dy 65+ Tb Cs Hg Au79+ Ir Pt 78+ Er 157 Tm Os Pt Ta Au Pb 81+ Ho Tl Hg Os Tm Bi Tl 80+ Pb Hf Hg Tl Tb Ta 194 Lu 200 Hg Re mass knownpo Hg 78+ Po Ir 190 Au Pb Pb Er 75+ Pt 20.0 Re Au Pb Bi Pb 82+ Po 84+ Hf Au Po m,g Tl 79+ Pt Bi Hg Au Intensity / arb. units Intensity / arb. units 0 Bi Pb Pb 81+ Tl 80+ Bi 82+ Ta 5 Hf Number of channels 2 Recording time 30 sec Bi Frequency / khz / Frequency Hz

10 HITRAP so far built / designed

11 Letter of Intent Realistic Stellar Nucleosynthesis Studies Involving Nuclear Excitation via Atomic-Nuclear Interactions in High Energy Density Plasma Environments L.A. Bernstein, M. Wiedeking, Chr. Kozhuharov, C. Brandau, Th. Stöhlker, A. Palffy, Ch. H. Keitel, V. Meot, G. Gosselin, P. Morel, E. Bauge, P.M. Walker, D. Schneider Lawrence Livermore National Laboratory, USA GSI-Helmholtzzentrum Darmstadt, Germany University of Heidelberg, Germany Helmholtzzentrum Jena, Germany Max Planck Institute for Nuclear Physics, Heidelberg, Germany CEA/DAM, Bruyeres-le-Chatel, France University of Surrey, Guildford, U.K. (GSI-GPAC approved)

12 Basic Idea Ionization IC/BIC Plasma Atom Nucleus DR NEEC/NEET/ DR-NEET IC internal (electron) conversion BIC bound internal conversion DR dielectronic recombination NEEC nuclear excitation by electron capture NEET nuclear excitation by electron transition

13 Radiative Recombination, Dielectronic Recombination and Nuclear Excitation by Electron Capture

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15 20 years later - Astrophys. J. 139, 776 (1964) 40 years later J.B..A. Mitchell et al, PRL. 50, 335 (1983), D.S. Belic et al PRL (1983), P.F. Dittner et al. PRL (1983) first experimental observations

16 Photorecombination in cosmic plasmas Courtesy D.W. Savin, Columbia Astrophysics Lab (CAL), New York, N.Y. electron ionized (stars, supernovae, galaxies, ) photoionized (radiation field) (PNebulae, x-ray binaries, AGNs, ) High T e DR Low T e DR Sun SNR PN XRBs Galaxies AGNs

17 NEEC first mentioned by Goldanskii & Namiot Phys. Lett. 62B (1976) Natural line widths ev Resonance strength 1 bev A. Pálffy, Z. Harman, W. Scheidt, PRA 73(2006)012715

18 Nuclear Excitation by Electron Capture, NEEC Motivation: NEEC has not been observed yet. The ionic state can influence the decay properties of a nucleus. The plasma energy couples to the nuclear degrees of freedom. Experimental challenges: widths, signal-to-noise, signature: The natural line widths of the nuclear levels of interest are orders of magnitude smaller than the energy spread in classical electron-ion scattering experiments. In e-ion collisions, the predominant process is radiative electron capture into vacant ionic states. It is a source of massive background at comparable energies.

19 Main Idea, Feasibility, Proposal (Challenge - only a few events per minute)

20 What would happen

21 Basic Idea for a NEEC experiment Illustrative Example: 238 U The first excited state in 238 U decays predominantly via L-IC (44.9 kev) Bare uranium ions bombard cold electron target with the appropriate energy an electron is captured into the L shell and the nucleus is excited. K-vacancies in uranium decay in sec, the L-electron goes to the K-shell, i.e. this partial decay width dominates the total one. The competing process of radiative recombination, RR, is very fast. The excited nucleus leaves the RR-background zone The excited nucleus can decay only via gamma emission i.e. slower by the conversion coefficient (270) The gammas can be detected in a background free zone in coincidence with ions which have captured one electron The colder the electrons the better. (The experimental proposal is currently being prepared.)

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25 New Detector in ESR Drives are being prepared at KVI

26 Experimental Storage Ring injection from SIS/FRS (ESR) electron target electron cooler recombination detector circumf m energies MeV/u ions up to U 92+ extraction to HITRAP / reinjection to SIS Schottky pick-up Cooled ion beams in well-defined ionic states

27 DR-Measurement Merged electron and ion beams Drift-tube defined variation of the relative ion-electron velocities Recombination Separation by the ESR dipol magnet Single particle detection (4π) α(e CM ) vrelσ E 1 1 β β N e i CM Ion R n e L U

28 Dielectronic Recombination of Li-like Gold

29 Li-like Xe51+

30 Li-like Xe 51+ Continuum electron are captures into series of Rydberg state up to the series limit for both types of excitation of the 2s electron: 2s 2s 2p 2p

31 Stochastic cooling at the ESR Long. Kicker Transv. Pick-up Combiner Station Transv. Kicker Long. Pick-up ESR storage ring Stochastic cooling - particularly efficient for hot ion beams Fixed ione trajectory and energy: 400 MeV/u)

32 KLL-DR of H-like Xe 53+ Xe s e Xe 2 l j 1 2 l j 2 K L L

33 DR of H-like U 91+ D. Bernhardt et al. Phys. Rev. A (R) (2011) Breit Interaction in dielectronic recombination of hydrogenlike uranium U 91 1s e U 90 2l nl j 1 j 2

34 energy spread [ ev ] Energy Resolution at ESR low collision energies (c.m.) high collision energies (c.m.) collision energies from mev to sub MeV present ESR (e-cooling): energy spread from e-beam kt = 120 mev kt = 100 ev Present TSR e-target kt = 2 mev kt = 20 ev present ESR (stochastic cooling) energy spread from ion beam dp/p = (1 ) NESR e-target kt = 5 mev kt = 10 ev NESR ion beam with dp/p = (1 ) electron energy (c.m.) [ ev ] resolution ~10 mev to ~10 ev

35 155 Gd At low relative ion-electron energies: First excited state at ev 1s binding energy = ev Conversion electron energy 857 ev Jasmin Soltani-Schirazi, PhD-thesis University of Heidelberg, 1983 (J. Soltani, W. Koenig, R. Mann, C.K.) (Hyperfine splitting?) Even more exciting the 7.6 ev in thorium 229

36 The 7.6 ev in Th-229

37 229 Th 9/ kev I=1 (M1) 28.29keV = I=49 (E2) 96.22keV = I=100 (M1) 53.61keV = 23.3 I=5.7 (M1+E2) kev = 12 I=1.5 (E2) keV = 4.22 E B (1s) = kev => NEEC (5/2+ -> E r = 186 ev E B (2p 3/2 ) = kev => NEEC (5/2+ -> E r = 860 ev 229 Th production rate (1cm Be-foil) > 10 6 per Th primary

38 FAIR: New Experimental Opportunities at Super-FRS/NESR? SIS Super-FRS e-target ELISE/AIC CR cooler Large yields of exotic ions (SFRS) Additional in-ring equipment e-target Extraction to FLAIR building Separate cooler and e-target Ultracold e-target (?) => boost of versatility, precision and sensitivity High-Energy Cave NESR Low-Energy Cave cooler gas-jet (SPARC / EXL) extraction to FLAIR

39 Summary and Outlook In time reversed reactions, we can augment resonance strengths by orders of magnitude if we are capable of finding (an) additional rapid decay channel (s). We will extend our search in regions of high (nuclear) excitation energies and/or angular momenta. Theoretical assistance and guidance needed.

40 In order to know that there is a mountain higher than Mount Everest, we do not have to drain the ocean

41 Transversal Electron Target Blue = Electron beam Red = Ion beam Wei Shi et al. Nucl. Instr. & Meth. B (2003) The photograph does not show the cathode.

42 Celsius Electron Cooler and Björn Gålnander

43 Uppsala Electron Cooler The cooler has been dismantled and the transported from Uppsala to Darmstadt two years ago.

44 Inner-Shell Electrons of Heavy Highly-Charged Ions as a Probe for the Nuclei Nucleus Wave functions of low-lying electron orbitals in U 91+ In heavy few-electron systems : significant overlap of s- and p 1/2 -electronic wavefunction with the atomic nucleus bound electrons are a sensitive probe of the nucleus (charge distribution, nuclear spin) isotope shift with DR: shift of a whole pattern by the same amount

45 Rate Coefficient [10-9 cm 3 s -1 ] Isotope Shift of Li-like 142 Nd 57+ vs. 150 Nd 57+ in Dielectronic Recombination Spectra e + A Nd 57+ (1s 2 2s 1/2 ) A Nd 56+ (1s 2 2p 1/2 18l j' ) j' > 5/2 j' = 1/2 A = 142 A = 150 shift 40 mev j' = 5/2 j' = 3/ Relative Energy [ ev ] shift 40 mev 25-Sep-2008 Christophor Kozhuharov SPARC_RO_

46 Carsten Brandau, et al. rate coefficient [arb. units] rate coefficient [arb. units] Preparation of Li-like Exotic First Dielectronic Recombination Measurements of Radioisotopes from Projectile Fragmentation Beams in the ESR Background: Schottky spectrum of the beam preparation in the ESR 3.0 DR of 237 U U 88+ (1s 2 2p 3/2 5l 3/2 ) typical intensities: 3-4x10 5 stored and cooled ions preliminary Pa 87+ (1s 2 2p 3/2 5l 9/2 ) typical intensities: 2-3x10 4 stored and cooled ions preliminary electron-ion collision energy (c.m.) [ev] DR of 234 Pa 88+