Properties of X-Rays Reference: “Elements of X-ray Diffraction”, 3nd Edition, B.D. Cullity, and S.R. Stock, Prentice Hall, NJ Chapter 1

X-ray source: Tube source: Rotation anode source Synchrotron radiation source Liquid metal jet X-ray source

Vacuum, thermionic emission, high voltage, and a target Braking radiationCharacteristic X-ray Auger electrons

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

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

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.

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

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

CrFeCuMo Z K  1, Å K  2, Å K , Å K  1, Å , filt. V, 0.4milMn, 0.4milNi, 0.6 milNb, 3mils , filt. Ti (Z = 22)Cr (Z = 24)Co (Z = 27)Y (Z = 39) Resolution, Å Critical potential, kV Operating conditions, kV: Target materials and associated constants 1 mil =0.001 inch = mm

Synchrotron radiation source Lorentz force: Electromagnetic radiation produced by relativistic charged particles accelerated in circular orbits. glish/lightsource.aspx

glish/lightsource.aspx Undulators  ultra-brilliant, single-wavelength radiation from the resulting interference patterns

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

Multicomponent system μ/ρ: For a substance containing several elements w i is the weight fraction of the element i

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

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

Sharp discontinuities at K, LI, LII, LIII, M,… absorption edges! luento/xray- absorption.html

Use of absorption for filtering function luento/xray- absorption.html

X-Ray detectors: Proportional Counters (  ) Microchannel Plates Semiconductor Detectors (  ) Scintillators (  ) Phosphors Negative Electron Affinity Detectors (NEADs) Single Photon Calorimeters

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

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?

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

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.

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

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

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

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

Scintillation Counter detector:

tillator.html

Scintillator (usually Tl doped NaI) UV photoelectron Relatively high count rate detector (>100,000 cps is possible) poor energy resolution

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

Si, Ge semiconductor detector (LN2 cooling required )! Spectrometry application! For spectrometry application without LN2 cooling Si drift detector

Position sensitive X-Ray detector Inel

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

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

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