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The Trouble With Technetium
Hywel Owen School of Physics and Astronomy University of Manchester
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A Tale of Two Physicists
Ernest O. Lawrence
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Emilio Segrè and the 37-inch cyclotron deflector foil
‘In February 1937 I received a letter from Lawrence containing more radioactive stuff. In particular, it contained a molybdenum foil that had been part of the cyclotron's deflector. I suspected at once that it might contain element 43. The simple reason was that deuteron bombardment of molybdenum should give isotopes of element 43 through well-established nuclear reactions. My sample, the molybdenum deflector lip, had certainly been intensely bombarded with deuterons, and I noted that one of its faces was much more radioactive than the other. I then dissolved only the material of the active face, in this way achieving a first important concentration of the activity. ‘
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Natural Molybdenum Each isotope can obviously undergo its own reactions, either from neutrons or otherwise. Isotope Abundance (atom %) Mo-92 15.84 Mo-94 9.04 Mo-95 15.72 Mo-96 16.53 Mo-97 9.46 Mo-98 23.78 Mo-100 9.63
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Mo-99/Tc-99m/Tc-99 143 keV Tc-99m isomerism
Seaborg and Segrè, Phys. Rev. 54(9), 772 Seaborg and Segrè, Phys. Rev. 55(9), 808 Tl-201 (made with a cyclotron, t1/2~3d) emits at 80 keV (through electron capture) which is not as good for imaging
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235U fission
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Fission Yields
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Fission Cross-Sections in U/Pu
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Segre Chart
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Fission Beta Decay
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A=98/99 Decay Chains Nuclide Halflife 99Y 1.470(7) s 99Zr 2.1(1) s
99Nb 15.0(2) s 99Mo 2.7489(6) d 99Tc 2.111(12)E+5 a 99Ru Stable
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Research and Power Reactors
Research reactors Better neutronics, but need high power (>20 MW) Easier fuel cycle: can extract targets out quickly and process them, needed to obtain Mo-99 Only 5 reactors meet these requirements
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Major producers of Mo-99
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Reactor and target
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Technetium Generators
Typical Mo-99 specific activity 3000 Ci/gm (0.6%) Typical price UKP , gives ~100 doses (depending on modality), GBq (3-7 Ci) 92,000 sold in USA in 2005 Total market around 600 MEuro, but this is artificially cheap because of cross-subsidy from nuclear research Only few companies worldwide doing either processing or packaging: General Electric (50%), MDS Nordion, Covidien (25%), Mallinckrodt, NTP ‘Demand is 200% of supply’ (Alan Perkins, BNMS)
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Some facts about Tc-99m usage
Nuclear Medicine USA 29 M (44%) Europe 9 M (22%) Hospital imaging: Computed Tomography Nuclear Medicine (85% Tc-99m) MRI 35 M procedures/yr (global) Primarily cardiac imaging e.g. post heart-attack Tc-99 Usage All Tc-99m 28 M Cardiac 12 M World weekly supply: 2g of 235U used, 0.11g Mo-99 provided $140 M
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Problems with the reactor method
Reactors are all very old, with disrupted replacement plans: MAPLE-1/2 cancelled : 4 disruptions : 5 disruptions May 2009 & October 2009 are shortage months when 3 reactors are down. Uranium enrichment 5% for power, e.g. PWR 20% for research 95% for Mo-99 (or bombs) LEU < 20% HEU >20% 95% of global HEU use is for Mo-99 production USA does not like HEU being shipped around in boxes
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Switching to LEU targets
LEU target issues 25 times more 239Pu generated (due to 238U n capture) but alpha contamination is about the same (due to 234U concentration during enrichment) Switching to LEU targets Use LEU (around 20% 235U) Needs about 5 times as much Uranium as a (95%) HEU target, since the 238U doesn’t do anything. No-one is using LEU and associated processing – yet Mo-99 purity will be about the same Target is not bigger, since you use different U density Use U foil target (8g/cm3) rather than UO2 (1.6 g/cm3) or extruded U/Al rods Use Cintichem process for extraction Still 50 Ci of waste per 1 Ci of Mo (c.f. 30:1 with 235U) (Vandegrift et al., Industrial & Engineering Chemistry Research 39(9), 3140 (2000)) Mushtaq et al., NIM B 267, 1109 (2009)
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Mo-99 Candidate Production Methods
Accelerated Incident Reaction Comments Reference Deuteron 98Mo(d,p)99Mo Segre and Lawrence Proton Neutron 100Mo(n,2n)99Mo Nagai & Hatsuwaka, JPSJ 78, (2009) 100Mo(p,2p)99,99mNb(β-)99Mo N/A 98Mo(n,γ)99Mo Reactor Mo W.Diamond, AECL Oct 2008 Ryabchikov et al., NIM B 213, 364 (2004) Be/Pb target Froment al., NIM A 493, 165 (2002) 235U(n,f)99Mo Reactor method ~1 GeV 238U(p,f)99Mo Lagunas-Solar, Trans.Amer.Nucl.Soc. 74, 134 (1996) Electron Gamma 100Mo(γ,n)99Mo 30 MeV Dikiy et al., Nuclear Physics Investigations (42), p (2004) 235/238U(γ,f)99Mo Photofission/RIB Coceva et al., NIM 211, 459 (1983)
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Mo-99 production R. Bennett et al., Nuclear Technology, 1999 vol. 126 (1) pp. 102 Based on development of high-current superconducting technology for energy-recovery linacs UK has significant expertise at Cockcroft/ALICE Typical parameters are 100 mA, 50 MeV electrons (for 15 MeV photons) Single target vs. multiple targets?
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Tungsten Target, Gamma Production, and Photofission
Haxby et al., Phys. Rev. 58(1), 92 (1940) Tungsten Target, Gamma Production, and Photofission 235U (also benefits from neutron reflection and fission cascade) 238U Berger and Seltzer, Phys Rev C 2, 621 (1970) Diamond, NIM A 432, 471 (1999)
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Photofission Yields De Clerq et al., Phys Rev C 13 (4), 1536 (1976)
P. Bricault, TRIUMF Diamond, NIM A 432, 471 (1999) ‘A radioactive ion beam facility using photofission’
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Photofission Method P. Bricault, TRIUMF
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Related target geometry (RIB)
P. Bricault, TRIUMF
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ALICE Accelerator Test Facility
Hz
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ALICE Cavities high current cavity under construction;
to be evaluated in 2010
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Liquid (Solution)/Solid Target for Photonuclear Mo (Kharkov)
Dikiy et al., Nuclear Physics Investigations (42), p (2004) Dikiy et al., EPAC’98 Either solid or aqueous solution target (Na2MoO4/K2MoO4) Yield in solution is very low, but yield in target is ok (e.g. ~1 Ci from 24h at 1mA Target should be enriched 100Mo to avoid production of other isotopes (expensive)
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Photonuclear Cross-Section in 100Mo
W.Diamond, AECL, Oct 2008 Around 100 Ci/g with 100kW/50MeV electrons into W About 2 atoms in 10,000 (cf ~10% in fission products) this requires a different (bigger?) generator normal generator 60 in 10000 Target design is crucial ‘Photofission is likely not practical’ Sabelnikov et al., Radiochemistry 48(2), 191 (2006) - report 390 mb with direct irradiation with 25 MeV electrons
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ORNL ORELA Target design (Diamond/Beene)
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Direct Proton Reactions
100Mo(p,pn)99Mo 100Mo(p,2n)99mTc 98Mo(p,γ)99mTc Kim et al., IEEE Nuclear Science Symposium Conference Record, NSS'07, N15-307 Scholten et al., Applied Radiation and Isotopes 51, 69 (1999) Uddin et al., Applied Radiation and Isotopes 60, 911 (2004) M. Challan et al., J. Nucl.Rad.Phys. 2(1), 1 (2007)
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Adiabatic Resonance Crossing (Rubbia)
Rubbia, CERN/LHC/97-04 Arnould et al., Phys. Lett. B 458, 167 (1999)
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Epithermal neutron capture in 98Mo
Ryabchikov et al., NIM B 213, 364 (2004)
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Resonant Neutron Capture
Isotope Abundance Abs (barn) Pb --- 0.171 204Pb 1.4 0.65 206Pb 24.1 0.03 207Pb 22.1 0.699 208Pb 52.4 Resonant Neutron Capture Lethargy Froment al., NIM A 493, 165 (2002) Van Do et al., NIM B 267, 462 (2009)
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65 MeV Protons into Be target (7 hour exposure)
Froment et al., NIM A 493, 165 (2002) Abbas et al. 601, 223 (2009) About 1 neutron per 8 protons
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Which is the best method?
Questions to answer Which is the best method? 238U Photofission 100Mo Photonuclear 100Mo Direct Proton 98Mo Epithermal Capture Probably photofission, but targets need comparison and optimisation Modelling software MCNPX GEANT FLUKA (EMPIRE-II) Nuclear reaction data Some discrepancies
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Carlo Rubbia patent Patent 2005/ (2005) Resonant neutron capture in Mo, possibly Na2MoO4 solution
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Cockcroft would like to develop a demonstrator Mo-99 facility
UK Plans and Elsewhere Cockcroft would like to develop a demonstrator Mo-99 facility 10mA, 50 MeV electrons as demo machine Full facility with hot cells probably on nuclear site, e.g. Sellafield Target design needs to be done as part of demo design TRIUMF have collaboration with MDS-Nordion Non-disclosure agreement! ORNL have done target work – in contact with them
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