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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

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Presentation on theme: "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"— Presentation transcript:

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

4 v Target v0v0 v1v1 v2v2 Braking radiation: x I V1V1 V2V2 V 2 > V 1

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

6 Excitation source K L1L1 L2L2 L3L3 K L1L1 L2L2 L3L3 Characteristics X-Ray photon k L1L1 L2L2 L3L3 Auger electron Radiative transition Nonradiative transition M }{ KK K2K2 K1K1 K (L) shell excitation  K (L) radiation, etc.

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

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

9 CrFeCuMo Z24262942 K  1, Å2.28961.93601.54050.70926 K  2, Å2.29351.93991.54430.71354 K , Å2.29091.93731.54180.71069 K  1, Å2.08481.75651.39220.63225 , filt. V, 0.4milMn, 0.4milNi, 0.6 milNb, 3mils , filt. Ti (Z = 22)Cr (Z = 24)Co (Z = 27)Y (Z = 39) Resolution, Å1.150.950.750.35 Critical potential, kV5.997.118.9820.0 Operating conditions, kV:30-4035-45 50-55 Target materials and associated constants 1 mil =0.001 inch = 0.025 mm

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

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

12

13 Absorption:  : linear absorption coefficient I 0 : X-ray intensity at x = 0  = (  /  )  ;  : density; (  /  ): mass absorption coefficient I0I0 I dx Lambert-Beer law http://www.helsinki.fi/~s erimaa/xray-luento/xray- absorption.html Reference:

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

15 (  /  ): true absorption; (  m /  ): scattering Small for Z >26 I0I0 I Scattering (elastic: same wavelength, Compton scattering: different wavelength ) Fluorescence (longer wavelength) x

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

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

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

19 X-Ray detectors: Proportional Counters (  ) Microchannel Plates Semiconductor Detectors (  ) Scintillators (  ) Phosphors Negative Electron Affinity Detectors (NEADs) Single Photon Calorimeters http://imagine.gsfc.nasa.gov/docs/science/how_l2/xray_detectors.html

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

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

22 Efficiency: f abs,w : f abs,d : effective excitation (  signals) f losses : counting losses window 11- f abs,w ~ 1

23 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.

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

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

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

27 Typical Gain ~ 10 4 -10 5. G = 10 4 Cu radiation on Ar gas filled proportional counter 304  10 4 = 3.04  10 6. Typical F 10 -10 farad. Small voltage  need further electronic amplification Bias larger enough (~ several KV)  avalanches (G saturated)  “Geiger counter” (long deadtime)

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

29 http://wanda.fiu.edu/teaching/courses/Modern_lab_manual/scin tillator.html

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

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

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

33

34 Position sensitive X-Ray detector Inel

35 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

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

37 * 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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