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Properties of X-Rays

Properties of X-Rays. Reference: “Elements of X-ray Diffraction”, 3nd Edition, B.D. Cullity , and S.R. Stock, Prentice Hall, NJ 2001. -- Chapter 1. http://en.wikipedia.org/wiki/X-ray http://chemistry.tutorvista.com/nuclear-chemistry/x-rays.html#. X-ray source: Tube source:

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Properties of X-Rays

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  1. Properties of X-Rays Reference: “Elements of X-ray Diffraction”, 3nd Edition, B.D. Cullity, and S.R. Stock, Prentice Hall, NJ 2001. -- Chapter 1 http://en.wikipedia.org/wiki/X-ray http://chemistry.tutorvista.com/nuclear-chemistry/x-rays.html#

  2. X-ray source: Tube source: http://en.wikipedia.org/wiki/X-ray_tube http://www.youtube.com/watch?v=7Shle-b0W0E http://www.youtube.com/watch?v=vruuVFH_Vro&feature=related Rotation anode source http://en.wikipedia.org/wiki/X-ray_tube http://en.rigaku-mechatronics.com/technology/technology01.html Synchrotron radiation source http://www.nsrrc.org.tw/ Liquid metal jet X-ray source http://www.excillum.com/Technology/metal-jet-technology.html

  3. Vacuum, thermionic emission, high voltage, and a target http://www.arpansa.gov.au/radiationprotection/basics/xrays.cfm Braking radiation Characteristic X-ray Auger electrons

  4. Braking radiation: Target v2 v0 v1 V2 > V1 v I V2 V1  x

  5. Characteristic X-ray K L M Auger Electrons K L M

  6. Nonradiative transition M } { Auger electron Characteristics X-Ray photon L3 L3 L3 L2 L2 L2 Excitation source L1 L1 L1 K K2 K1 Radiative transition K K k K (L) shell excitation  K (L) radiation, etc.

  7. K K I Critical potential  Characteristic X-ray  Cooling anode  Better heat dissipation  higher power (applied potential  electron beam current (Typical tube source: 50 kV and 40 mA→2 kW water

  8. Rotation Anode Source Rotating the anode  more cooling time for the part hit by energetic electrons  higher power is allowed! http://www.antonine-education.co.uk/Pages/Physics_GCSE/Unit_3/Triple_01_X-rays/triple_01.htm Rotating anode and cooling  higher power

  9. Target materials and associated constants 1 mil =0.001 inch = 0.025 mm

  10. Synchrotron radiation source Lorentz force: http://www.nsrrc.org.tw/english/lightsource.aspx Electromagnetic radiation produced by relativistic charged particles accelerated in circular orbits.

  11. Undulatorsultra-brilliant, single-wavelength radiation from the resulting interference patterns http://www.nsrrc.org.tw/english/lightsource.aspx

  12. Absorption: Lambert-Beer law Reference: http://www.helsinki.fi/~serimaa/xray-luento/xray-absorption.html I I0 dx : linear absorption coefficient I0: X-ray intensity at x = 0  = (/) ;  : density; (/): mass absorption coefficient

  13. Multicomponent system μ/ρ: For a substance containing several elements wi is the weight fraction of the element i http://physics.nist.gov/PhysRefData/XrayMassCoef/tab3.html

  14. Fluorescence (longer wavelength) I I0 Scattering (elastic: same wavelength, Compton scattering: different wavelength ) x (/): true absorption; (m/): scattering Small for Z >26

  15. True absorption: http://www.helsinki.fi/~serimaa/xray-luento/xray-absorption.html For fluorescent, photoelectron is not necessary as long as the electrons at the ground state are excited to a higher energy level

  16. Sharp discontinuities at K, LI, LII, LIII, M,… absorption edges! http://www.helsinki.fi/~serimaa/xray-luento/xray-absorption.html

  17. Use of absorption for filtering function http://www.helsinki.fi/~serimaa/xray-luento/xray-absorption.html

  18. X-Ray detectors: Proportional Counters () • Microchannel PlatesSemiconductor Detectors () Scintillators () PhosphorsNegative Electron Affinity Detectors (NEADs)Single Photon Calorimeters http://imagine.gsfc.nasa.gov/docs/science/how_l2/xray_detectors.html

  19. Important aspects of a detector: (1) Losses (2) Efficiency (3) Energy resolution Losses v Time v Time v Random loss (Inevitable) v Serious loss

  20. Random losses (always there) Resolving time of the detector electronic: ts the maximum rate without losses: 1/ts. Losses  as rate . Counting loss Detector 2 Use filters Noise? Quanta Detected /second Detector 1 Quanta Absorbed /second

  21. Efficiency: fabs,w: fabs,d: effective excitation ( signals) flosses: counting losses window 1 1-fabs,w ~ 1

  22. Different detector: different wavelength range to detect! Efficiency of a 10-cm-long gas ionization chamber as a function of energy, for different gases at normal pressure.

  23. Energy Resolution: For most of the detectors Voltage produced  energy of X-ray quanta. Counting rate W V Pulse amplitude Resolution R resolution 

  24. Gas filled detector: Proportional and Geiger counter Wire anode cathode C X-rays R electron-ion pairs produced: E: X-ray energy; ei: effective ionization potential ei for He, Ar, and Xe: 27.8, 26.4, and 20.8 eV; Using Cu K radiation, Ar gas: n = 8040/26.4 = 304

  25. Gain may be defines as N: # of electrons reaching wire anode; n: # of electron produced by X-ray quanta

  26. Typical Gain ~ 104-105. G = 104 Cu radiation on Ar gas filled proportional counter 304104 = 3.04106. Typical F10-10 farad. Small voltage  need further electronic amplification Bias larger enough (~ several KV) avalanches (G saturated)  “Geiger counter” (long deadtime)

  27. Scintillation Counter detector: http://www.bruker-axs.de/fileadmin/user_upload/xrfintro/sec1_6.html

  28. http://wanda.fiu.edu/teaching/courses/Modern_lab_manual/scintillator.htmlhttp://wanda.fiu.edu/teaching/courses/Modern_lab_manual/scintillator.html

  29. Scintillator (usually Tldoped NaI) UV photoelectron http://en.wikipedia.org/wiki/Scintillation_counter Relatively high count rate detector (>100,000 cps is possible) poor energy resolution

  30. Semiconductor detector: Excellent energy resolution Usually cooling is required! Reasonable count rate Find more on: http://wwwmayr.informatik.tu-muenchen.de/konferenzen/Jass04/courses/4/Tobias%20Eggert/TalkIoffe.pdf

  31. Si, Ge semiconductor detector (LN2 cooling required )! Spectrometry application! For spectrometry application without LN2 cooling Si drift detector http://144.206.159.178/ft/787/31793/552178.pdf

  32. Position sensitive X-Ray detector Inel

  33. Safety Precautions  Electric shock  Radiation Hazard: user’s responsibility (your own and others) * Four main causes of accidents (1) Poor equipment configuration, e.g. unused beam ports not covered, interlock system is not engaged. (2) Manipulation of equipment when energized, e.g. adjustment of samples or alignment of optics when x-ray beam is on. (3) Equipment failure, e.g. shutter failure, warning light failure. (4) Inadequate training or violation of procedure

  34. Failure to follow proper procedures has been the result of: rushing to complete a job,  fatigue  illness, personal problems, lack of communication, or  complacency

  35. * Radiological Signs * Everyone should participate the safety training course offered by the University before actually doing X-ray or other radiation related experiments.

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