Materialforschung Mit Positronen An Der Strahlungsquelle .

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Materialforschung mit Positronen an derStrahlungsquelle ELBEMaterials Research w/ Positrons at theRadiation Source ELBEAndreas WagnerNuclear Physics DivisionInstitute of Radiation -RehbergKrause-RehbergGeburtstagskolloquiumMember of the Helmholtz AssociationAndreasWagnerWagnerI ysics I I www.hzdr.dewww.hzdr.de Andreas

Outline Why using anti-matter formaterials research? How to obtain decent amountsof positrons?Courtesy: R. Krause-Rehberg / M. Butterling Applying pulsed beams: positron annihilation lifetimespectroscopy for bulk materials, fluids, gases, and thin films GiPS – the Gamma-induced Positron Source MePS – the Monoenergetic Positron SourcePage 2Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Fate of positrons in matterPositrons slow down to thermalenergies in 3-10 ps. After diffusing insidethe matter positrons are trapped invacancies or defects.Kinetics results in trapping rates about105 times larger than annihilation rates:defect concentrations down to 10-7 areaccessible.metals(screening)e para-Psinsulatorsvoidsortho-Psfree2g0.2 nstrapped2g0.5 nsself2g0.125 nscapture2g1.0 nsself3g142 nsspin-flip2g1 - 100 nsPage 3Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Sensitivity of Positron Annihilation scatteringSTM/AFMPositron AnnihilationLifetime SpectroscopyPage 4Geburtstagskolloquium Reinhard Krause-RehbergPositron AnnihilationLifetime SpectroscopyMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Isotopes, reactors, acceleratorsProduction of positrons in weak interactions (mediated by W’s)neutron(u d d)νee 27Al(p,n)27Si(β νe,4.2 s) 27AlW (u d u)protonSumitomi Heavy Industries Cyclotron18 MeV protons, 50 µA beam currentPage 5Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Isotopes, reactors, acceleratorsProduction of positrons through electromagnetic interactions (photons)Use intense source of photons for pair production Capture-neutron gamma-rays from reactor113Cd(n,γ)114Cde-FRMII MunichKUR KyotoTU Delfte-e γe Bremsstrahlung from electron accelerators or lasers (Changsha/Wuhan, Osaka/Hyogo,ELI-NP Buccuresti)AIST, Tsukuba, JapanELBE, DresdenPage 6Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Positrons from acceleratorsNC-LINAC in bunched mode 2.8 GHz / 1 µs / 100 Hz / 10 µAlinear storageconvertermoderatorebuncher Asamplechopperbuncher Be 1 µs10 eV3 ms5 ns2 ns250 psSC-LINAC in CW mode38 ns / 26 MHzEPOS facilitychopperbunchersamplemagnetic transportconvertermoderatoree 10 ps2 ns2 keVPage 7Geburtstagskolloquium Reinhard Krause-Rehberg250 psMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Positrons from accelerators1.6 mA, 40 MeV (64 kW)CW electron acceleratorBremsstrahlung16 MeVGamma-inducedPositronscoherent IR-radiation3 – 230 µmelectrons 34MeVradiation biologydetector tests 110 mTHz radiation100 µm – 3 mmpulsed, mono-energeticpositrons 0.2 – 20 keVSPONSOR: mono-energeticpositrons 0.2 – 30 keVfrom 22NaPage 8Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

What about bulk materials, fluids, gases ?SC-LINAC in CW mode38 ns / 26 MHzbuncherchoppersamplemagnetic transportconvertermoderatoree 2 nsradiatore-10 psγe e-sample10 ps100 psGiPSThe Gamma-inducedPositron annihilationSpectroscopy10 psPage 9Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Positron production using electronM. Butterling, et al.,bremsstrahlungNucl. Instr. Meth. B 269(2011)2623Positron beams for material researchA.Wagner, et al.,Defect & Diffusion Forum 331(2012)41E e 16 MeVI e 900 µAf 26 MHzσ t 10 psAnnihilation Lifetime Spectroscopy(Coincidence) Doppler BroadeningAge-momentum Correlationphoton beam2 cm diameter108 cm-2 s-1Nb foil: 10-3 X0studies performed so far:- animal tissue- metals and alloys- (neutron-activated) reactor materials- water, glycerol from 10 C to 100 CPage 10Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Positrons: backgnd for nuclear physics exp’ts Kapton at16 MeV electronenergy Hard bremsstrahlung produces a huge amount of positrons via pair productioninside the target material. High-energy photons act as a volume source ofpositrons throughout the entire volume.Seite 11Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Gamma-induced Positron Spectroscopyconventional LINAC modepulsed RF, highest energytypically pile-up problems 1 µs / 100 HzF.A. Selim, D.P. Wells, J.F. Harmon, et al.Nucl. Instr. Meth. A 495 (2002) 154SC-LINAC in CW modehighest average power –high yield and low pile-up38 ns / 26 MHzHigh resolution lifetime spectrum withsignal to noise ratios of better than 105:1using gamma-gamma coincidencetechniques for background reduction.Lifetime spectra are free from artefacts. Long lifetimes reveal atomic defectscaused by neutron-induced damage. Can (and how) defects be removed bythermal annealing?Page 12Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Physics with GiPS: RPV steelReactor vessel steel becomes brittle due to neutroninduced defects like open-volume defects. The atomicdefects act as seeds for cracks.Collaboration with ReactorSafety Division. Preferential formation of double vacancies Thermal annealing (290 C) not sufficient to remove defects!Page 13Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Physics with GiPS: FluidsConventional lifetime measurements: dissolve 22Na and dispose it afterwardsPositrons from bremsstrahlung homogeneously distributed, sharp time stampTarget is temperature-stabilized, continuouslycirculated, degassed, dry-nitrogen flushed.Kapton tube targetPositron PhysicsOrtho-Positronium (o-Ps) in a fluid forms a bubblegiven by its zero-point energy and the surfacetension.fluide e-We know estimate the change of the o-Ps pick-offannihilation lifetime with temperature in a bubblecreated by the o-Ps itself .R.A. Ferell, Phys. Rev., 108,167, 1957S.J. Tao, J. Chem. Phys., 56,5499, 1972M. Eldrup et al., Chem. Phys., 63,51, 1981Page 14Geburtstagskolloquium Reinhard Krause-Rehbergo-Ps142 nsp-Ps125 psMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Physics with GiPS: Positron(-ium) ChemistryExperiments with water are in variance with a simple bubble-type model.Extension: chemical reactions between radiolysis products of the slowing-down of thepositron Ps chemistry.Courtesy: Maik Butterling, S V.Stepanov Radicals are positron scavengers which reduceannihilation lifetimes. Extended bubble model including chemistry[S.V. Stepanov et al., Mat. Sci. Forum 607] andenergetics of hydrated e aq and e-aq (what are therelaxation times of un-/polar media?) Chemistry of radiolysis directly accessible sincethe probe creates the ionization itselfPage 15Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

The Mono-energetic Positron Source MePSIn order to perform depth-resolved annihilation lifetime and Doppler-broadeningspectroscopy of thin films, Univ. Halle and HZDR have set-up the MePS source.4 ns chopper78 MHz bunchersample20 cm Pb 3.2 m concreteshieldingSC-LINAC beam 30 MeV, 0.1 mA 1.625 MHz repetition rate615 ns spacing2 keV magnetictransport systemPage 16Geburtstagskolloquium Reinhard Krause-Rehbergpost-accelerator-1.5 16 kVMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

17Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

18Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

MePS setupMartin-Luther-Universität Hallechopper and bunchersectionelectrostaticpost acceleratormagnetic transportsystemPage 19Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

The Mono-energetic Positron Source MePSRadiation shielding aroundthe target amounts to about:1 Hyle of lead1 Hyle of concrete1 Hyle 1 VAs3/cm2 10 tPage 20Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Pore size and o-Ps lifetimesfluide e-Diss. S. Thränert, MLU 2008Page 21Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Experiments at MePS: nano-channeled SiNano-channeled silicon produced by etching for Ps storage and release.Courtesy: R. Brusa, Univ. TrentoTune the nano-channel size to optimize the influenceof thermalization times (the smaller-the-better) andlowest Ps temperature (the bigger-the-better).Improve Ps output by capping with various materialsfor Ps reflection. - Measure Ps lifetimes and yielddepending on channel size and capping.Page 22Geburtstagskolloquium Reinhard Krause-RehbergR. Brusa, et al., PRL 104 (2010) 243401Member of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Experiments at MePS: low-k dieelectricsReduction of RC time constants change switching speed of CMOS devices.CMOS deviceM. Jungmann, et al.,Journal of Physics: Conference Series 443(2013) 12088K.B. Yeap, et al.,Journal of Materials Research 28(2013)1262Page 23Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Future work: In-situApparatus for In-situ Defect ydrogen diffusion:speed of loading/deloadingprocess, e.g. Hao et al, J. Phys.Chem. Lett. 1 (2010) 2968RamanspectrometerTalk on Tuesday by P. Hruska (H-loading)Wednesday by M. John (sputtering)XPSanalysisunitPage 24Geburtstagskolloquium Reinhard Krause-RehbergHydrogen storage capacity:decoration of defects in eirradiated Nb, e.g. J. Cizek etal., Phys. Rev. B 79 (2009)054108Member of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Future workion source(not seen)manipulatorBeam diagnostics and differentialpumpingH2 reactore detectorse or ion beamfor H-depthprofilingXPS analysis and PALS chambercellUHV system at the 6 MVeffusionion beamload lockelectron beamevaporatorXPS chamberHigh-voltage cage on top of MePSPage 25Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

The teamHelmholtz-Zentrum Dresden-RossendorfW. Anwand, M. Butterling#,T. E. Cowan*, J. Ehrler*,M.O. Liedke, K. Potzger, T.T. Trinh*, A.W.*also at Technische Universität Dresden#now at TU Delftand many collaboratorsS.V. Stepanov, D.S.Zvezhinskiy (ITEP, MEPhI)C. Hugenschmidt, M. Reiner (TU Munich)F. Selim (U Bowling Green)M. Kraatz, E. Zschech (Fraunhofer IKTS)A. Uedono (Univ. Tsukuba)R. Brusa, L. Ravelli (Univ. Trento)Martin-Luther-Univ. Halle-WittenbergR. Krause-Rehberg,P. Fobe, M. John, C. Kessler,M. Jungmann, I. Smirnov, A. MüllerA.G.Attalah, N. Hinsche,J. Haeberle, A. Pohl, A. Krille,B. Wehrlich, H. Benkwitz, L. Büttner,S. Bölling, G. JakobH2OMnSiZnOlow-klow-knano-SiFunding provided by BMBF (05K2013) and thanks to theFederal Ministry for Economic Affairs and Energy of Germanyfor funding.Page 26Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

27Geburtstagskolloquium Reinhard Krause-RehbergMember of the Helmholtz Association Andreas Wagner I Institute of Radiation Physics I www.hzdr.de

Geburtstagskolloquium Reinhard Krause-Rehberg Andreas Wagner I Institute of Radiation Physics I www.hzdr.de Member of the Helmholtz AssociationPage Positrons slow down to thermal energies in 3-10 ps. After diffusing inside the matter positrons are trapped in vacancies or defects. Kinetics results in trapping rates about

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