Varenna Summer School July 2009? Physics with many Positrons Positron Sources & Positron Beams Christoph Hugenschmidt Technische Universität München
What is many? Galaxy: 1.5 10 43 e + /s! = 1 lake + 1 anti-lake Como per second! NEPOMUC: 9 10 8 e + /s = 3.6 kj per year Christoph Hugenschmidt 2
Outline Positron Sources β + Sources Pair Production Positron Beams Positron Moderation Positron Beam Facilities NEPOMUC Beam Facility Summary Christoph Hugenschmidt 3
Outline Positron Sources β + Sources Pair Production Positron Beams Positron Moderation Positron Beam Facilities NEPOMUC Beam Facility Summary Christoph Hugenschmidt 4
Beta Decay: Nuclide Chart red: β +,EC proton no. 1, neutron no. +1 blue: β proton no. +1, neutron no. -1 black: stable p n e + υ e Christoph Hugenschmidt 5
β + - Looking for the Right Nuclide Characteristics of β + sources: positron yield half life source production set-up endpoint energy intensity source replacement reactor, cyclotron in-situ, ex-situ implantation depth spin polarization Christoph Hugenschmidt 6
β + Sources Nuclide Half-life E max [MeV] E m [MeV] v/c f [%] E γ [MeV] Appl. Prod. 11C 20.4 min 0.96 0.37 0.81 100 - PET Zyc 13N 9.96 min 1.20 0.50 0.86 100 - PET Zyc 15O 122 s 1.73 0.65 0.90 100 - PET Zyc 18F 110 min 0.633 0.21 0.71 97 - PET Zyc 22Na 2.6 y 0.546 0.20 0.70 90 1.275 t, S, Beam Zyc 26Al 7.4 105 y 1.17 82 1.809 27Si 4.2 s 3.79 100-44Ti/44Sc 49 y 1.47 0.45 0.85 95 1.157 48V 16 d 0.695 0.30 0.78 50 1.312, 0.984 57Ni 36 h 0.864 34 1.378 58Co 70.8 d 0.475 0.19 0.68 15 0.811 S, Beam Reac 64Cu 12.7 h 0.653 0.27 0.76 19 - S, Beam Reac 68Ge/68Ga 271 d 1.90 0.99 0.94 90 - t, S Zyc 72Se/72As 8.4 d 2.5 52 0.834 3.34 1.36 0.96 13-89Zr 78.4 h 0.90 22 - µ+ 2.20 s 52.3 1.00 100 - Christoph Hugenschmidt 7
Source Production Reactor: n-activation of isotopes thermal neutrons: fast neutrons: 63 Cu(n th,γ) 64 Cu 58 Ni(n f,p) 58 Co Accelerator: 45 MeV protons 27 Al(p,x) 22 Na (e.g. x=α,d) http://www-nds.iaea.org/medical/index.html Christoph Hugenschmidt 8
The Standard: 22 Na 22 11 22 + Na Ne + β + ν + 10 Energy Spectrum and term scheme Christoph Hugenschmidt 9
β + Sources for Lab Experiments Handling of β + sources: Examples: evaporation 64 Cu drying of solution 22 NaCl or 22 NaCO 3 thin foils activation of thin Cu-foil chemical separation intrinsic source 58 Co activation of 58 Co in a sample geometrical/intensity limit: self absorption of positrons: e.g. 22 Na ~100mCi Christoph Hugenschmidt 10
Outline Positron Sources β + Sources Pair Production Positron Beams Positron Moderation Positron Beam Facilities NEPOMUC Beam Facility Summary Christoph Hugenschmidt 11
Intense Positron Sources Pair Production: γ e + e E γ > 2 m e c 2 bright γ-sources High Intensity: I>10 7 e + mod/s high Z σ PB ~ Z 2 lne Ł Bremsstrahlung Accelerators Synchrotron Ł Decay of excited nuclear states Reactor: Fission γ s Reactor: (n,γ)-reactions Christoph Hugenschmidt 12
Principle: Bremsstrahlung Target Former e+ source at LLNL: e - beam: 100 MeV, 300 µa Christoph Hugenschmidt 13
Pairproduction at a Synchrotron? E > 2 m e c 2 Christoph Hugenschmidt 14
Undulator Driven Pair Production M. Kuriki, Japan Christoph Hugenschmidt 15
Gamma s at Reactors Fission: Available energy: 201 MeV / fission 180 MeV prompt 7 MeV γ 21 MeV fission fragments 6 MeV γ absorption in W pair production POSH at Delft reactor Christoph Hugenschmidt 16
POSH IRI Delft Former source: In-situ activation of 64 Cu and pair production Now: pair production in W Christoph Hugenschmidt 17
(n, γ) Reactions: 113 Cd 113 Cd (n, γ) 114 Cd 26000 barn! 2.3 γ / n E γ > 1.5 MeV 0.66 e + / n Positron spectrum: E m 800 kev! B. Krusche and K. Schreckenbach, NIM A 295 (1990) 155 Christoph Hugenschmidt 18
Positron Yield e+ production Cd W converter optimum γ e+ e+ d NEPOMUC: Cd/Pt B. Krusche and K. Schreckenbach, NIM A 295 (1990) 155 Christoph Hugenschmidt 19
Outline Positron Sources β + Sources Pair Production Positron Beams Positron Moderation Positron Beam Facilities NEPOMUC Beam Facility Summary Christoph Hugenschmidt 20
Aim: Monoenergetic Positron Beams Main beam characteristics: Positron Moderation kinetic energy E 0 band width E beam intensity I And: size, shape, divergence... brilliance B I d = 2 2 Θ E from R. Krause-Rehberg Typical moderation efficiency: 10-4.. 5 10-3 Christoph Hugenschmidt 21
Modertor-Material Requirements: negative positron work function: F + < 0 e+ leave the solid, sharp longitudinal energy and low angular spread high stopping power annealed crystal less defect trapping large diffusion length recrystallisation of polycrystal grainsize > diffusion length single crystal, F + depends on crystal orientation clean and plane surface lower energy spread less surface trapping Some materials and their F + : W: -3 ev, Cu: -0.25 ev, Pt: -2 ev, Ni: -0.8 ev,... solid rare gases SiC: 2.1 ev Christoph Hugenschmidt 22
Moderator-Geometries reflection venetian blinds transmission wires frozen rare gas intrinsic (Cu, Pt) combination (trans. & refl.) see e.g. P. Coleman, Positron Beams Christoph Hugenschmidt 23
Bandwidth Maxwell-distribution Gullikson et al. PR B 32, 1985, 5484 Christoph Hugenschmidt 24
Angular Spread W(110)+O2 @ RT Cu(111) @ 23K and 300K D. A. Fischer et al.; PR B 33,1986, 4479 Christoph Hugenschmidt 25
Monoenergetic Positron Beam From MeV positrons to a mono-energetic beam: E e+ ~kev E < 2 ev 1 ev NEPOMUC: Pt as converter AND moderator: φ + Pt = -1.95(5) ev C. Hugenschmidt et al. NIM B 198 (2002) 220 Christoph Hugenschmidt 26
Degradation and Recovery C. Hugenschmidt et al., 2002 Christoph Hugenschmidt 27
Designing a Re-Moderator Solid state moderator: transmission + simple beam guidance - thin foils (~100nm), surface flatness - lower moderation efficiency reflexion - sophisticated beam guidance + higher moderation efficiency + easier to handle Think about: phase space beam optics see following lecture Gas moderator: transmission, inelastic scattering, drift field + high efficiency - beam injection / extraction, differential pumping... Christoph Hugenschmidt 28
Ni in Transmission Energy > 5 kev: Primary beam diameter: 10 mm Remoderated beam diameter: 90 µm Remoderation efficiency: 5 % Oshima et al. J. Appl. Phys. 103, 094916 2008 Christoph Hugenschmidt 29
W(100) in Reflexion Positron thermalization and diffusion to the surface Emission due to negative Φ + Extraction by electrical and magnetic fields Parameters: E in = 1 kev E out = 10-200 ev 20 ev E T 40 mev ε mod = 20 % ε tot = 7 % d out < 2 mm d FWHM = 2 mm Reflexion geometry C. Piochacz et al. (2007) Christoph Hugenschmidt 30
Experimental Setup at NEPOMUC Gas Moderator Electrodes Decelerating potential Focusing electrodes and gas inlets e + beam 300 mm Retarding potential and annihilation target B. Löwe, E21 NEPOMUC TUM, 2007 Christoph Hugenschmidt 31
Outline Positron Sources β + Sources Pair Production Positron Beams Positron Moderation Positron Beam Facilities NEPOMUC Beam Facility Summary Christoph Hugenschmidt 32
Positron Beams Typical features of positron beam facilities: source: moderator: intensity (e+ mod /s): lab large scale facility 22 Na ( 68 Ge, 64 Cu ) W (Ni, Ne, Kr ) 10 4 10 6 Bremsstrahlung, linac W ~10 8 Tsukuba fission γ s, reactor W 8 10 7-2 10 8 Delft n capture γ s, reactor Pt 9 10 8 NEPOMUC Christoph Hugenschmidt 33
Overview: Positron Beam Facilities 1. Lab-beams: W-moderators (mainly used) ~40 running Solid rare gas moderator 2. Micro-beams Two Schools : Small-source Remoderation 3. Large scale facilities: LINAC-based 3 running, ~6 planned Reactor-based fission n-γ 4. Polarized beams remoderated beams 5. Trap-based beams pulsed beams Christoph Hugenschmidt 34
Lab I: W-Moderated Beam University Halle Christoph Hugenschmidt 35
Lab II: Kr-Moderated Beam H. Heußer, C. Hugenschmidt et al. Appl. Surf. Sci. 149(1999)49 Christoph Hugenschmidt 36
LINAC I: KEK KEK: 1.5 GeV 0.75 kw 10nC/pulse pulse width: 10 ps repetition rate: 50 Hz >10 7 e+/s Christoph Hugenschmidt 37
LINAC II: FZ Rossendorf EPOS facility in FZR (under construction) Christoph Hugenschmidt 38
Trap-Based Positron Beam Principle: Buffer gas cooling instead of solid moderator Positron accumulation in a magnetic and electrostatic trap Pulsed release of trapped positrons further lecture UCSD, Surko et al. Christoph Hugenschmidt 39
Outline Positron Sources β + Sources Pair Production Positron Beams Positron Moderation Positron Beam Facilities NEPOMUC Beam Facility Summary Christoph Hugenschmidt 40
NEPOMUC NEutron induced POsitron Source MUniCh Principle: n therm Cd Pt γ fast e + slow e + Neutron Source FRM II Positron Beam NEPOMUC n capture γ emission γ e + e - conversion e + moderation e + emission Christoph Hugenschmidt 41
NEPOMUC NEutron induced POsitron Source MUniCh Mono-energetic positron beam of highest intensity Since March 2008 new in-pile positron source: 9 10 8 e+/s C. Hugenschmidt et al. NIM B 192 (2002) 97, Appl. Phys. A 74 (2002) S295, NIM B 221 (2004) 160, NIM A 554 (2005) 384 C. Hugenschmidt et al. Appl. Surf. Sci. 252 (2006) 3098 C. Hugenschmidt et al. NIM A 593 (2008) 616 Christoph Hugenschmidt 42
NEPOMUC at FRM II SR 11 Remoderator PLEPS Switch SPM interface PAES CDBS Open Beamport: Ps - Christoph Hugenschmidt 43
NEPOMUC NEutron induced POsitron Source MUniCh Christoph Hugenschmidt 44
Application with Many Positrons Christoph Hugenschmidt 45
Summary Positron sources β + emitter & pair production High intensity beams of moderated positrons Positron beam facilities Linac & reactor NEPOMUC: experiments with high positron beam intensity 9 10 8 e + /s, 1 kev Bright future of exciting experiments with many positrons! Christoph Hugenschmidt 46