Introduction to IBA – The RBS and ERD techniques Anastasios Lagoyannis Tandem Accelerator Laboratory Institute of Nuclear and Particle Physics N.C.S.R. “Demokritos”
Outline Ion Beam Analysis Theoretical background Rutherford Back Scattering Elastic Recoil Detection Analysis Conclusions A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Pros / Cons They are generally least destructive and are suitable for use with delicate materials. They are to a certain extent multielementary and produce high‐accuracy quantitative results. They require little or no preparation of the sample with the result that a specimen (like an artifact) could be directly analyzed. Only very small quantities (mg) of sample are needed. They permit the analysis of a very small portion of the sample by reducing the diameter of the ion beam to less than 0.5 mm. Some damage cannot be avoided (thermal, carbon buildup etc.)! A VdG type of accelerator is required. In most of the cases the experiments are carried out in vacuum chambers. Several experimental issues need to be addressed, thus a minimum knowledge of nuclear physics (experimental and theoretical) is mandatory. No direct information about the chemical environment can be produced. The analysis concerns only a few microns below the surface of the samples. In most of the cases, a combination of techniques is required to solve a problem, and this implies time consuming experiments! A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Ion Beam Analysis Ion Beam Analysis (IBA) is based on the interaction , at both the atomic and the nuclear level, between accelerated charged particles and the bombarded material. When a charged particle moving at high speed strikes a material, it interacts with the electrons and nuclei of the material atoms, slows down and possibly deviates from its initial trajectory. This can lead to the emission of particles or radiation whose energy is characteristic of the elements which constitute the sample material A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Theoretical Background I Nuclear Reaction: The interaction between two nuclei which results in the emission of nuclei and/or gamma rays. Cross Section: The probability of a nuclear reaction to occur N det σ = Ω ꞏ N N ꞏ inc tar A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Theoretical Background II Scattering: When a charged particle impinges on a material, it interacts with the electrons and the nuclei of the material. The result of the interaction is the loss of energy and the change of trajectory of the initial ion. Energy Straggling: Loss of kinetic energy per length unit Inelastic collisions with the electrons and the nuclei A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Theoretical Background II A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Depth Profiling • Rutherford Backscattering Spectroscopy (RBS) • Nuclear Backscattering Spectroscopy (NBS) YES • Elastic Recoil Detection Analysis (ERDA) • Nuclear Reaction Analysis (ΝRA) • Particle Induced γ –Ray Emission (PIGE) • Charged Particle Activation Analysis (CPAA) • Particle Induced X‐Ray Emission (PIXE) NO • Neutron Activation Analysis (NAA) • Secondary Ion Mass Spectroscopy (SIMS) A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
The 5.5 MV VdG Tandem accelerator @ I.N.P. A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Tandem Layout neutron irradiations γ ‐ calorimetry d‐filled gas‐cell Tritiated Ti‐target (rotating) μ‐PIXE Atomic physics Auger external Spectrom. beam multipurpose scattering chamber 4 HPGe detect. array Charged‐particle induced X rays RBS , NRA, ERDA … γ ‐ spectrometry charged‐part. irradiations A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
AGLAE Accelerateur Grand Louvre d’ Analyse Elementaire A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Sample Size Selection There are three possibilities Under Vacuum External Beam No size limitation Small samples (1 to 10 cm) No vacuum conditions Can withstand vacuum (no wood) Flow of He Preferably good electrical conductivity Limited accuracy Greater accuracy Microbem Small samples (less than 1 cm) Elemental mapping possibilities A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
External Beam Setup A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Rutherford Backscattering Spectroscopy Rutherford backscattering (RBS) is ideal for depth‐profiling heavy elements on lighter substrates. The beam ions impinge on the sample and they are Elastically Back Scattered Identification of material The identification of the sample Is done with the use of basic ideas: Conservation of Energy and Momentum High sample Ζ Higher Energy at the scattered beam A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Rutherford Back Scattering Quantification The detected ions (known) N Unknown det N = tar Ω ꞏ N ꞏ σ inc Detector’s solid angle Cross section Number of beam’s particles (known) (Analytical form unknown) (known) EXCEPT for RUTHERFORD Cross Section 2 ( 1 4E ) 2 dσ 1 z Z e ꞏ ꞏ = 4 θ dΩ 4πε sin 0 0 2 A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Detection Apparatus Beams used • Protons from 0.5 to 3 MeV Probe larger depths • Heavier ions (12C, 160) 10 to 20 MeV Probe only surface layers Higher mass resolution Higher depth resolution Most commonly used detectors are Surface Barrier Detectors (SSB) • Various thicknesses (μm) and apertures (mm 2 ) • They work only under high vacuum • Can detect the energy of the particle (resolution ~ 15 keV) • Can’t detect the mass of the particle Sample considerations • Small size ( few cm) • Capable of being under vacuum (no wood e.t.c.) • Preferable good electrical conductivity A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Experimental Setup Motor driven goniometer Motor driven goniometer Suitable for channeling studies Great angular accuracy (0.01 deg.) 4 – axis target movement Up to 4 targets Place for PIGE detector Water cooling available A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Conceptual Examples M 1 < M 2 or A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Conceptual Examples 80000 9000 8000 60000 7000 6000 Counts Counts 5000 40000 4000 3000 20000 2000 1000 0 0 200 400 600 800 1000 1200 1400 1600 1200 1300 1400 1500 1600 1700 1800 Channel Channel A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Conceptual Examples 4000 4000 3000 3000 Counts Counts 2000 2000 1000 1000 0 800 1000 1200 1400 1600 1800 0 Energy 800 1000 1200 1400 1600 1800 Energy A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Conceptual Examples 15000 Cu Cu 6000 Si Si Total Total 10000 Counts 4000 Counts 5000 2000 0 0 400 600 800 1000 1200 1400 1600 1800 400 600 800 1000 1200 1400 1600 1800 Channels Channels A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Conceptual Examples 25000 14000 Si 20000 Cu Cu 12000 Si Total 10000 15000 Counts Counts 8000 10000 6000 4000 5000 2000 0 0 400 600 800 1000 1200 1400 1600 1800 600 800 1000 1200 1400 1600 1800 Channel Energy A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Conceptional Examples 2 MeV 4 He, θ=165 o E n e rg y [k e V] 4 00 600 800 10 00 12 00 1 400 1 600 180 0 200 0 22 00 24 00 2 600 2,0 00 1,9 00 Au on SiO 2 1,8 00 1,7 00 1,6 00 1,5 00 1,4 00 1,3 00 1,2 00 Counts 1,1 00 1,0 00 900 800 700 600 500 400 300 200 100 0 60 8 0 10 0 120 1 40 160 1 80 20 0 2 20 24 0 260 2 80 30 0 3 20 34 0 360 3 80 400 4 20 44 0 4 60 48 0 500 5 20 C h a n n e l A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
Conceptional Examples 2 MeV 4 He, θ=165 o Energy [keV] 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2,000 Au/SiO 2 multilayers 1,900 1,800 1,700 1,600 1,500 1,400 1,300 1,200 Counts 1,100 1,000 900 800 700 600 500 400 300 200 100 0 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 Channel A. Lagoyannis Institute of Nuclear and Particle Physics NCSR “Demokritos”
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