Positron-Annihilation Lifetime Spectroscopy Using Electron .

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Positron-Annihilation LifetimeSpectroscopy using ElectronBremsstrahlungAndreas WagnerNuclear Physics DivisionInstitute of Radiation PhysicsMember of the Helmholtz 014Physics I ,Goa2014 Andreas Wagner I Institute of Radiation Physics

Outline MotivationCourtesy: R. Krause-Rehberg / M. Butterling Accelerator-based positron production and annihilation studiesat a superconducting electron LINAC: What marks the differenceto reactors and radio-isotope sources? Applying pulsed beams: positron annihilation lifetimespectroscopy at thin films, bulk materials, and fluids Development of a pixelated detection system for positionsensitive positron annihilation lifetime measurements andexperiments with structured targets and tomographic imagereconstructionPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Isotopes, reactors, acceleratorsProduction of positrons in weak (W ) or electromagnetic interactions (γ)neutron(u d d)νee e-W e-e γe-(u d u)protonFree proton decay is forbidden by energy conservation we need the proton inside a nucleus where it undergoes β -decayPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas 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 currentPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas 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-e γFRMII Munich Bremsstrahlung from electron acceleratorsAIST, Tsukuba, Japane-e-ELBE, DresdenPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Positrons from acceleratorsAccelerators can produce intense and pulsed slow positron beams.LINear ACcelerators are favored due to their high beam power and time structure.A) normal conducting LINAC (AIST)E 50 MeVIpeak 100 mAbeam powertbunch 1 µs500 Wfrep 100 Hzsophisticated converter designsand heavy shielding neededB) superconducting LINAC (HZDR)E 50 MeVIaverage 1 mAbeam powerfrep 10 MHz50 kWstack of 50100 µm thick W foilsEPOS water-cooledconverterPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas 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 storageconvertermoderatoresubh. bunchersamplechopperbunchere 1 µs10 eV3 ms5 ns2 ns250 psSC-LINAC in CW mode38 ns / 26 MHzEPOS facilitychopperbunchersamplemagnetic transportconvertermoderatoree 10 ps2 ns2 keVPositron and Positronium Chemistry, Goa 2014250 psMember of the Helmholtz AssociationAndreas 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 testsTHz radiation100 µm – 3 mmpulsed, mono-energeticpositrons 0.2 – 20 keVmono-energeticpositrons 0.2 – 30 keVfrom 22NaPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas 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 psPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Positron production using electronbremsstrahlungM. Butterling, et al.,Positron beams for material researchNucl. Instr. Meth. B 269 (2011) 2623E 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 done so far:- water, glycerol from 10 C to 100 C- animal tissue- metals and alloys- neutron-activated reactor materialsPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Positrons: backgnd for nuclear physics exp’tsKaptonHard 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 11Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas 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?Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas 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!Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Physics with GiPS: KaptonAnnihilation lifetime in Kapton has been under debatefor quite some time. Here, we try to get ameasurement without source correction.Kaptonapplied cuts on Germaniumand BaF2 detector energy signalreduce background frominteractions outside the sample consistent single positron lifetime of (381 1) pstwo components show larger χ2Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas 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 .o-Ps142 nsp-Ps125 psR.A. Ferell, Phys. Rev., 108,167, 1957S.J. Tao, J. Chem. Phys., 56,5499, 1972M. Eldrup et al., Chem. Phys., 63,51, 1981Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Physics with GiPS: Fluids 2 U r E 2mPsstationary Schrödinger eqn. R r R r R0 jl kr j0 kr sin krkrh2 2 2E0 28mPs r0 4me r02Ansatz: spherical Bessel fct.1st non-trivial solutionzero-point energyEsurf 4 r02 E0 Esurf 0 r0fluid e e- 2 23e 02m r 8 r0 0 2 r0 4 4.3 A16me 4 0 2 c a0 1.06 A22m e m cPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Physics with GiPS: Positron ChemistryExperiments with water are in variance with a simple bubble-type model.Extension: chemical reactions between radiolysis products of the slowingdown of the positron 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]describes data well. Relevance for PET diagnostics since 2γ / 3γ ratiois affected. Chemistry of radiolysis directly accessible sincethe probe creates the ionization itselfPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Towards imaging of defectsMaterial failures impose a significant threat to the integrity and the safetyof technical systems. A thorough understanding of the microscopic originand the development of defects requires advanced methods. andthe questsof today early daysof materialanalysisPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

MotivationEstablish a non-destructive and non-intrusive method which allows forspatially resolved positron-lifetime spectroscopy. Reconstruct PET-likeimages plus positron annihilation lifetime.Possible Applications (list not complete): Porosimetry Medicinein-beam positron lifetime spectroscopy during hard x-raytumor therapy Engineering pre-failure diagnostics of micro fracturesfuel rod inspectionAPS Physics & Society Newsletter2011. R. Hargraves, R. MoirPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Prerequisites Intense source of positrons with deep penetration (cm)Accurate time-stamping of positron creation ( 10 ps)Position-sensitive positron detectors (mm)Time-resolution for lifetime spectroscopy ( 100 ps)Efficient data acquisition3-D image reconstruction 15 MeV X-raysCW LINACSiemens LSO PETin-house (physics)in-house (physics)in-house (medicine)sampleee-Gamma-induced Positron SpectroscopyPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Towards 2/3-D positron lifetime tomography Two position-sensitive photon detectors with 169 elements eachLSO-based commercial 13x13 PET pixeldetector SiemensLutetium oxyorthosilicateLu2SiO5:Ce4 mm x 4 mm x 20 mm LSO crystalscourtesy: university hospital Dresden Each crystal array read out using 4 PMT Summed PMT signal - gamma energy Correlation of individual PMT signals - position Positron annihilation time given by sumover all 8 PMT involvedPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Electronics (VME)block detectortransimpedance NIMamplifierCFD25 mLEVMECAENV1495FPGACAENV1290TDCCAENV965QDC100 nsdelayCESRIO4ROCMulti-hit and multi-event bufferedreadout in VME block mode and readoutwith 10 µs dead time for 36 channels(QDC & TDC) per event.Throughput is about 10 MB/s sustained.Data acquisition and analysis frameworkusing Multiple-Branch System MBS byHelmholtz-Center for Heavy Ion Research(GSI).Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Calibrations t 225 ps𝐸 𝐸1 𝐸2 𝐸3 𝐸4𝑡 1(𝑡 𝑡 𝑡 𝑡 )4 1 2 3 4- taccelx 𝐸1 𝐸2 𝐸3 𝐸4𝐸1 𝐸2 𝐸3 𝐸4; y 𝐸1 𝐸3 𝐸2 𝐸4𝐸1 𝐸2 𝐸3 𝐸4Calibration done using 7 cm x 7 cm aqueous 18F sourcew/ 200 MBq (T½ 2 h) produced in-house.Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Sample casesSiSiO2Proof of principle, first testSimple 2D target proof of principle simple back-projection method3D target Reconstruction of data as a function of life timeReal world sample (cutout from 91.4 T magnet coil) What we can learn from our methodPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Setup and results: 2D image reconstructionall tt 2 σt511 keVsample511 keVSiSiO2Sample selected to give balanced positron yield.Lifetime-gated 2D reconstructed image by back-projection.Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

3D reconstruction3D tomography applied forthe first time using bulkvolume positron production.Target is rotated in 2 deg.steps and the image isreconstructed using a cubical(30 mm)3 voxel space andback-projection algorithm.Bremsstrahlung beamγγPTFEFeCuAl0 180 Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Maximum Likelihood Expectation MaximizationAluminiumSteelIterative method for image reconstruction based on aalgorithm developed in PET[L.A. Shepp, Y. Vardi, IEEE-MI 2 (1982) 113].CopperSolves the inversion problem numerically where onehas a system matrix M, an a-priori unknown sourcedistribution s and a measured distribution r.Mˆ s rstep 1allpromptPositron and Positronium Chemistry, Goa 2014The system matrix has a size of132 x 132 x 180 x 303 138 x 109.longMember of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

MLEMAluminiumSteellonggateCoppershortgatestep 2allpromptlong2nd IterationPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

MLEMAluminiumSteellonggateCoppershortgatestep 5allpromptlong5th IterationPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

MLEMAluminiumSteellonggateCoppershortgatestep 10allpromptlong10th IterationPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

MLEMAluminiumSteellonggateCoppershortgatestep 20allpromptlong20th IterationPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Positron and Positronium Chemistry, Goa 2014prompt / allMember of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

MLEMGating on positron lifetimes with225 ps timing resolution.AluminiumSteelCopperallNow the Al is clearly discriminated against thesurrounding Teflon.promptPositron and Positronium Chemistry, Goa 2014prompt / allMember of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Lifetime-sensitive analysisB-field coilCourtesy: Jochen WosnitzaCut through the record coil which reached 91.4 Tpeak field. Coil is fed by the world’s largestcapacitor bank w/ 50 MJ stored energy.Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Tomography: B-field coilTeflonZylon Copperyzx48 h measurement time, 316 GB, 1.6 G events324 M filtered coincidencesPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Lifetime-sensitive analysis: B-field coilPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Lifetime-sensitive analysis: B-field coilτ 1.48 nsNow, we select specific voxels and determine the annihilation lifetimes for spatiallyseparated regions. Since the voxel is identified as an ensemble over all possiblelines-of-response between two detector crystals, the lifetime distribution is aconvolution as well. Some real physics questions needed Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

ExtensionsDigital Silicon Photomultiplier (dSiPM)ModuleDPC3200-22-44(819200 pixel each)###Courtesy:Digitally counting thenumber and the time ofarrival of scintillationphotons (here LYSO)Philips Digital Photon CountingPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

ExtensionsCRTdigital Silicon Photomultiplier (dSiPM)Employ the scaled accelerator radio frequency (13 MHz)via a phase-locked loop (PLL) as dSiPM system clock.- Intrinsic synchronization for optimal timing resolution.- 170 ps FWHM seem possibleenergy resolutionScintillation materialsCollaborative effort within gamma-ray imaging group atparticle-therapy center Oncoray.(Courtesy: J. Petzoldt, K. Römer, G. Pausch, et al.)Positron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

SummarySummary: Accelerator-driven positron production Annihilation lifetime spectroscopyfor fluids, reactor materials First results for 3D tomographyPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

The teamApply for beam time: deadlines 1stweeks in May and NovemberHelmholtz-Zentrum Dresden-RossendorfWolfgang AnwandMaik ButterlingThomas E. Cowan*Fine FiedlerFabian Fritz *Mathias Kempe † *A.W.*also at Technische Universität DresdenMartin-Luther-Univ. Halle-WittenbergReinhard Krause-RehbergC. KesslerP. Fobeand all the collaboratorsA.Ulbricht, E. Altstadt (HZDR)S.V. Stepanov, D.S.Zvezhinskiy (ITEP, MEPhI)Thank you for attentionPositron and Positronium Chemistry, Goa 2014Member of the Helmholtz AssociationAndreas Wagner I Institute of Radiation Physics I www.hzdr.de

Positron and Positronium Chemistry, Goa 2014 Andreas Wagner I Institute of Radiation Physics I www.hzdr.de Member of the Helmholtz Association Isotopes, reactors, accelerators Production of positrons through electromagnetic interactions (photons) e-e γ e-e-Use intense source of photons for pair production

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