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Depth Profiling with Low-Energy Nuclear Resonances

first some information about: Experimental background – the lab in Bochum Scientific background – Ion Beam Analysis and Nuclear Astrophysics. Depth Profiling with Low-Energy Nuclear Resonances. Ruhr-University of Bochum. H.-W. Becker, IAEA May 2011

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Depth Profiling with Low-Energy Nuclear Resonances

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  1. first some information about: Experimental background – the lab in Bochum Scientific background – Ion Beam Analysis and Nuclear Astrophysics Depth Profiling with Low-Energy Nuclear Resonances Ruhr-University of Bochum H.-W. Becker, IAEA May 2011 CRP: Reference Database for Particle Induced Gamma-ray Emission (PIGE)

  2. The Lab in Bochum Ruhr-Uni-Bochum 4 MV Dynamitron Tandem 500 keV – open air – single ended 100 kV – Implanter (not shown)

  3. The NRRA set-up in Bochum P = 2x10-9 mbar The 4 summing crystal 12x12 inch NaI(TL) with borehole high efficiency ( 50% photopeak efficiency at 2 MeV) integrating over angular distributions summing cascades into one peak

  4. Ion Beam Analysis and Nuclear Astrophysics

  5. Nuclear Resonance Reaction Analysis example 15N(p,a g)12C samplee E = ER E > ER Wirkungsquerschnitt [rel.] Detektor Strahlenergie [MeV] E = ER E > ER detector resolution for identifing the -ray only

  6. What determines the depth resolution in NRRA ? sample beam stopping power and total energy resolution: • 1.) resonance width Γ • 2.) beam energy resolution ΔEbeam • 3.) Doppler broadening ΔED

  7. stopping power: total energy resolution: to get a feeling:  1nm requires 70 eV resolution at 400 keV • 1.) resonance width Γ • 2.) beam energy resolution ΔEbeam • 3.) Doppler broadening ΔED e.g. for Si ~ 70 eV at room temperature by tilting the sample sub-nm resolution possible

  8. The 500 kV machine in Bochum: Lewis-peak Ep = 417 keV Resonanz in 29Si total resolution ~ 70 eV (mainly Doppler broadening) HV – ripple 30-40 eV 1 nm 20 eV stability:

  9. The ultimate resolution: 21Ne(p,)22Na, Ep = 272 keV Resonance 21Ne solid target (at 8 K !) resonance width 1 eV beam resolution 10 eV Dopplerbroadening 17 eV Lewis peak normal thick target yield Phys. Rev. B 58 1103 (1998)

  10. some proton induced resonances between 150 keV and 500 keV: Nuclear Resonance Reaction Analysiswith Proton Induced Low Energy Resonances

  11. One example – Diffusion studies in Olivin (making use of the isotope sensitivity of NRRA) Motivation: mechanical properties microscopic properties There is a correlation between diffusion and plastic flow pinning down temperature, pressure and time-scales from observation Knowledge of the diffusion parameters necessary !

  12. Measurement of diffusion processes in the laboratory: e.g.: A + B -> AB Natur Experiment A AB time scale B AB B 100 mm A 10 nm 100000 years ~ 8 days temperature scale , Q = activation energy production of layers with well defined stoichiometry Chemical potential

  13. Investigation of Si diffusion in Olivin Olivin (Fe,Mg)2SiO4 Testfall: Si Diffusion in Olivin (Diffusionskonstanten aus SIMS Messungen bekannt) native sample artificial Olivin layer enriched in 29Si (PLD) R. Dohmen, S. Chakraborty, H.-W. Becker Geophys. Res. Lett. 29 (2002) 261-264

  14. results: reference layer, ~ 35 nm dick first temperature process second temperature process concentration diffusion constant in good agreement with our earlier data depth [nm]

  15. Handbook of Modern Ion Beam Material Analysis (1995) information appears to be poor ….

  16. but lot of data are available from Nuclear Astrophysicsand increasingly from Material sciencea first attempt to collect the data (~ 1995)

  17. … but a lot of data available and still coming It would be nice to evaluate, extract and bring in a comprehensive form for material analysis: • The reaction and the abundance of the isotope • Resonance energy ER • Q-value or excitation energy • Resonance strength  or cross section  • Resonance width  • Non resonant cross section, next resonance •  - ray energies, plots of spectra would be useful • Meaning of the values for practical purposes

  18. summary: • Nuclear Reaction Analysis with low energy resonances can be a powerfull tool for depth profiling in the nm range • There are quite a few reonances between 150 kV und 500 kV offering various opportunities for applications • Sensitivity for isotopes offers special applications • Probably most if not all necessary data are available • Data evaluation collection and translation into material science lenguage desirable …

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