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RFQ Neutron Generator FFAG’11 Applications of Compact Accelerators Hywel Owen Cockcroft Institute/University of Manchester Cyclotrons PSI Cyclotron 590 MeV 2.2 mA, 1.3 MW Scaling FFAGs 1950/60s: Electron Models 2000s: Proton Models (Swept-frequency RF) Kyoto Proton FFAGs F. T. Cole, R.O. Haxby, Rev. Sci. Inst. 28(6), 403 (1957) The Internal Neutron Initiator (INI) Concentric foils of Po-210, Au-197 and Be-9 - Mixed under strong compression - (Munroe shaped charge) The External Neutron Initiator http://www.youtube.com/watch?v=zOlg0TBFfMs Operation Teapot, ‘Tesla’ was the first test of an ENI Only has to work once, but reliably, and with the correct timing! D-D and D-T Neutron Generators Q=3.27 MeV ~2.5 MeV neutrons, 3-5 MeV accelerator Q=17.590 MeV ~14.1 MeV neutrons, 100 kV accelerator • Many different variants, but all involve gaseous ions being accelerated to strike a hydride target • Typical voltages are ~100-150 kV, giving c. 10^9 neutrons/s into 4π • Target is e.g. Scandium Deuteride coated onto a Ag, Cu or Mo substrate • Good method of making monochromatic, pulsed neutrons • All design suffer from relatively poor lifetime (1000-10000 hours operation) • Tritium systems have to be handled carefully because of radiological leakage (1- 2 Ci of Tritium) • Be aware of ‘kinematical collimation’ Application: Borehole Logging • By measuring difference between eletrical and neutron porosity measurements, can tell if hydrogen-containing material around the logger is hydrocarbon or water – Oil prospecting • Uranium borehole logging looks for prompt fission using auxiliary detector, e.g. gamma rays. • Complementary to other borehole techniques, e.g. gamma spectroscopy The ‘Betatron Bomb’ Operation Tumbler-Snapper ‘George’ used a electron betatron to generate X-rays to induce photofission Advantage of the betatron is the faster rise-time of the initiating pulse. No public information about energies, but need about 15 MeV X-rays for photofission in the Plutonium-239 pit; can be done with c. 2.5 MeV electrons ‘George’ Detonation Early Kerst Betatrons 25 MeV 2.3 MeV? 300 MeV Phys. Rev. 58, 841–841 (1940) RFQ Neutron Generator • Increased energy allows greater yield but with larger size/cost • Protons or deuterons accelerated • Variety of targets possible – Pressurised D2 gas – Beryllium Applications of neutrons • Activation prompt gamma – Ore-grading/sorting • Direct radiography – Imaging of mechanical parts for ageing – Imaging of hidden objects (e.g. smuggling) – Imaging of dense materials (e.g. AWE) • Prompt fission detection – SNM detection • Differential scattering – Low-Z materials detection, e.g. explosives Application of neutron methods • A great deal of commercial/govt. interest • Large number of neutron techniques • Limitations – Technically-available flux – Size and shielding required – Activation issues – Dose to possible scanned people – Detector cost limits (HPGe is expensive) • Commercial take-up so far limited Application: Explosives detection with neutrons See e.g. Buffler, Radiation Physics and Chemistry 71 (2004) 853–861 Low-Z Target Systems • Many low-Z reactions are possible • Inverse kinematic reactions are possible (i.e. heavy ion onto light target) to improve kinematic collimation – But ion sources and accelerators are more complex; research machines only • Will only look here at X(p,n)Y reactions Thresholds for Different Reactions Kononov, Nuclear Instruments and Methods in Physics Research A 564 (2006) 525–531 • 1.7 MeV reaction threshold • Solid or liquid lithium target • Example: 3 MeV proton ‘dynamitron’ (electrostatic machine) • Useful flux of neutrons requires large currents – 10^12 n/s requires 1 mA – Liquid targets, complex cooling • Arrangement of neutron moderator/absorber modifies spectrum to peak at optimum energy for BNCT, 4 eV to 40 keV – Boron Neutron Capture Therapy Boron Neutron Capture Therapy Boron Neutron Capture Therapy with Reactors Beryllium Targets • Similar to Lithium targets • Advantage over spallation at low energy Applied Radiation and Isotopes 67 (2009) S258–S261 BNCT with FFAG-ERIT • Elegant method – multiple passes through thin Be target – Increased yield, lower required current, better neutron spectrum • FFAG needed due to large equilibrium size between scattering excitation protons and damping from re-acceleration e.g. Mori et al., PAC’09 • Thick target Be using 30 MeV protons • Moderator block shapes neutron spectrum for efficient n-capture • Used for commercial niche isotope production (e.g. brachytherapy) Nuclear Instruments and Methods in Physics Research A 601 (2009) 223–228 Low-Energy Spallation and Target Power 197 MeV protons on Pb 230 MeV protons on W (10 cm diameter) Owen et al, Annals of Nuclear Energy, 2011 Application: n-Capture Isotope Production Technetium-99m (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 235U fission Technetium Generators Typical Mo-99 specific activity 3000 Ci/gm (0.6%) Typical price UKP 400-600, gives ~100 doses (depending on modality), 100-250 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) Mo-99 Possible Production Methods Accelerat Incident Reaction Comments Reference ed Deuteron Deuteron 98Mo(d,p)99Mo Segre and Lawrence Proton Neutron 100Mo(n,2n)99Mo Nagai & Hatsuwaka, JPSJ 78, 033201 (2009) Proton Proton 100Mo(p,2p)99,99mNb(β-)99Mo N/A Neutron 98Mo(n,γ)99Mo Reactor Mo W.Diamond, AECL Oct 2008 Ryabchikov et al., NIM B 213, 364 (2004) Proton Neutron 98Mo(n,γ)99Mo Be/Pb target Froment al., NIM A 493, 165 (2002) N/A Neutron 235U(n,f)99Mo Reactor method Proton Neutron 235U(n,f)99Mo ~1 GeV Proton Proton 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.191-193 (2004) Electron Gamma 235/238U(γ,f)99Mo Photofission/RIB Coceva et al., NIM 211, 459 (1983) 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? 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) 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’ Photofission Method P. Bricault, TRIUMF Related target geometry (RIB) P. Bricault, TRIUMF 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 ORNL ORELA Target design (Diamond/Beene) Direct Proton Reactions 100Mo(p,pn)99Mo 100Mo(p,2n)99mTc 98Mo(p,γ)99mTc Kim et al., IEEE Nuclear Science Symposium Conference Record, 2007. 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) Small Cyclotrons From 10 MeV… …to 235 MeV (still compact?) Proton therapy covered in Roger Barlow’s talk Small Cyclotrons (Presentation by U. Amaldi at UAM Madrid, 2009) The Oniac • Tandem electrostatic accelerator, but folded up • Limited to around 10 MeV • Envisaged for protons, but perhaps other species? • Tranverse dynamics not yet investigated • T.b.c. – ‘to be constructed’ Beasley et al., IPAC’10 Application: Fluorine-18 Production • Enriched O18 water target • Automated pharmacy – Piped product from cyclotron to drug preparation • Short lifetime – local production • Main product FDG for PET Typical target power few kW The (Humble) Electron Linac Bremsstrahlung from 10-20 MeV electrons striking W or Cu targets The Rhodotron • λ/2 coaxial cavity • Energy limited by external return B field • High power possible at low energy • Electrons only? The Radiatron • High power FFAG Betatron • Looks very similar to original Kerst-type • But useful for low energy applications Application: Cable Processing • Excellent Flame Resistance • Improved Durability and Toughness • Higher Current-Carrying Capability • Greater Chemical Resistance • Easier Installations (Small Diameters, Flexible Stranding) • Typically normal-conducting linac c. 10 MeV, 10-50 kW • Scanning horn to process large area with uniformity Application: X-Ray Portal Scanners • Very widely applied • Accelerators used are 2-10(200) MeV with Bremsstrahlung converters • Used in a variety of settings • Portal monitors • Mobile scanning • Multiple electron energies or tomography are the hot topics right now – Give greater discrimination • Imaging processing is crucial They’re not all obvious!
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