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TARGISOL winterschool subjects: Diffusion Surface chemistry High temperature materials GPC

TARGISOL winterschool subjects: Diffusion Surface chemistry High temperature materials GPC Ion Sources, beams & applications Radiochemistry Ion Beams and Applications AMS. Most TI relevant talks: Isotope extraction at ISOL facilities - M. Turri ó n

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TARGISOL winterschool subjects: Diffusion Surface chemistry High temperature materials GPC

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  1. TARGISOL winterschool subjects: • Diffusion • Surface chemistry • High temperature materials • GPC • Ion Sources, beams & applications • Radiochemistry • Ion Beams and Applications • AMS • Most TI relevant talks: • Isotope extraction at ISOL facilities - M. Turrión • Release measurements at ISOLDE and GSI - U. Köster • The Miedema Model as a tool for the estimation of release and adsorption properties - Jörg Neuhausen • Influencing the work function in hot cavity ion sources - B. Marsh • K and Na radioactive multi-charged ion source - C. Eleon

  2. Radioactive Ion Beams: Production • In flight: very thin target • ISOL (Isotope Separation on-line): thick target • Spallation, Fragmentation, Fission Container Targets Ion Source Magnet Incident beam (protons, deuterons, alpha…) Radioactive ion beam Isotope extraction at ISOL facilities - M. Turrión, Targisol

  3. Radioactive Ion Beams Incident beam Ion beam • Radioactive atoms must reach the ion-source, be ionized and mass separated before they decay •  half life of the produced isotope - Release properties depend on the delay time due to: - diffusion inside the bulk material - effusion towards the ionization source (random walk in the container and transmission line and adsorption/desorption processes) Isotope extraction at ISOL facilities - M. Turrión, Targisol

  4. Release Two subsequent steps: Diffusion from the place of creation to the surface of the target Effusionin the enclosure until the ionization source • Container: • 20 x 2 cm cylinder of Ta • Target material: • Liquid La, Pb, Sn • Metal foil/powder Nb, Ti, Ta.. • Oxides CaO, MgO • Carbides SiC, UC, ThC • Ion-source • Surface • Plasma • Laser • Fluorination CF4 or SF6 Targets Container Effusion process Ion Source Desorption /Adsorption Diffusion process Incident beam (protons, deuterons, alpha…) Isotope extraction at ISOL facilities - M. Turrión, Targisol

  5. 2d x Analytical solution: infinite foil of thickness 2d • Infinite foil of thickness 2d • c0 initial particle concentration uniformly distributed in the foil at time t=0 The short time solution The long time solution Isotope extraction at ISOL facilities - M. Turrión, Targisol

  6. Database Diffusion and effusion with Monte Carlo • TARGISOLproject • Releaseprocess: • Diffusion: • D0, Ea, T • Effusion: • (sticking time) • t0, DHa, T tsorp adsorbent surface time 1/t0 is the frequency factor Ha the adsorption enthalpy • Database is accessible via URL: • http://www.targisol.csic.es Isotope extraction at ISOL facilities - M. Turrión, Targisol

  7. ISOLDE target and ion source unit Release measurements at ISOLDE and GSI - U. Köster, ISOLDE

  8. Release delays Release measurements at ISOLDE and GSI - U. Köster, ISOLDE

  9. Target preparation

  10. Analytical release model J.R.J. Bennett et al., Nucl. Instr. Meth. B126 (1997) 117. Nucl. Instr. Meth. B204 (2003) 211. • Analytical model difficult to extend to: • more complicated target geometries • effusion of ions influenced by electric fields • pulsed driver beam: > 1 GW/cm2 during 2 ms  thermal cycling of target, radiation enhanced diffusion,... Release measurements at ISOLDE and GSI - U. Köster, ISOLDE

  11. Monte Carlo release models C.J. Densham et al., Nucl. Instr. Meth. B126 (1997) 154. B. Mustapha and J.A. Nolen, Nucl. Instr. Meth. B204 (2003) 286. Mario Santana-Leitner, PhD, 2004 (http://www.ganil.fr/eurisol/ ) • Monte Carlo program adaptable to all target and ion source geometries including various physical processes, but: • difficult to deduce diffusion and desorption data from direct fit • complete on-line test is an expensive method to test new materials Release measurements at ISOLDE and GSI - U. Köster, ISOLDE

  12. Potential target materials for 8,9,11Li production Release measurements at ISOLDE and GSI - U. Köster, ISOLDE

  13. TARGISOL database: diffusion

  14. Monte Carlo: Diffusion D (2450 K) =10-14 m2/s=10-10 cm2/s

  15. Important prerequisites for RIB production • A volatile species has to be released from the target. Must be more volatile than target material Thermo chemically: its release enthalpy must be lower than the sublimation enthalpy of the target material • Subsequently, this species has to be transported to the ion source (they should not be deposited e.g. in the transfer line) Adsorption enthalpy on the construction material has to be low The Miedema Model as a tool for the estimation of release and adsorption properties - Jörg Neuhausen, PSI

  16. Enthalpy diagram of Release and Adsorption Processes release adsorption The Miedema Model as a tool for the estimation of release and adsorption properties - Jörg Neuhausen, PSI

  17. The Miedema Model allows a fast calculation of many metal combinations allows semi-quantitative statements about: • Release properties of targets • Adsorption on Metal surfaces • Shows the periodicity of these Properties Can give strong indication for choice of materials for separation processes, thus reducing the amount of experimental work to be done The Miedema Model as a tool for the estimation of release and adsorption properties - Jörg Neuhausen, PSI

  18. Choice of target and construction material Enthalpy of desorption for Ta surface [kJ/mol] The Miedema Model as a tool for the estimation of release and adsorption properties - Jörg Neuhausen, PSI

  19. Surface Ionization High Ionization efficiency - High work function - High operating temperature if  - WI is negative - Efficiency is greater for elements with low I.P Influencing the work function in hot cavity ion sources - B. Marsh, Manchester

  20. Hot cavity surface ion source High Ionization efficiency - Now independent of work function - High operating temperature Long life - Low vapor pressure - High chemical stability Influencing the work function in hot cavity ion sources - B. Marsh, Manchester

  21. Candidate materials and optimization Elemental materials easily satisfy the requirements of highand highTm Re W Mo  5.2 eV 4.9 eV 4.9 eV Tm 3422 oC 2623 oC 3186 oC J. Appl. Phys., Vol. 88, No. 7, 1 October 2000 Temperature Dependence : constant - corresponding to clean surface. Above 1700K: increases to up to 7eV 1200 - 1700K: Influencing the work function in hot cavity ion sources - B. Marsh, Manchester

  22. K and Na radioactive multi-charged ion source - C. Eleon, GANIL

  23. Cs Rb K Na Li K and Na radioactive multi-charged ion source - C. Eleon, GANIL

  24. Rhenium source Cs Rb K Na Li T = 2000 K K and Na radioactive multi-charged ion source - C. Eleon, GANIL

  25. TRImP ion catcher – a thermal ioniser Thermal calculations using Femlab Beam from the separator (i.e. 21Na) TrappedRadioactiveIsotopes: micro-laboratoriesfor FundamentalPhysics R. Kirchner, NIM B70 (1992) 186-199 (* for 208Pb ions, 2300 K, ** ta and t for 238U ions, 2800 K) Diffusion: Delay parameter m0=p2.D/d2D=D0.exp(-EA/kT) D: Diffusion coefficient  D0, EA: Arrhenius coefficients Effusion: Mean delay time t=1/n=c(ta+tf) ta=C1.exp(C2.DHa/T) ta, tf: sticking and flight times DHa: Enthalpy of adsorption Ionization: Ionization efficiency  hi=Na/(1+Na)a=ni/n0=exp((j-Wi*)/kT) N: Amplification factor  a: Degree of surface ionization ni,n0: ion and neutral densities Amplification factor < number of collisions (c)

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