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-rayhttp://chemistry.tutorvista.com/nuclear-chemistry/x-rays.html#

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 sourcehttp://www.nsrrc.org.tw/

Liquid metal jet X-ray sourcehttp://www.excillum.com/Technology/metal-jet-technology.html

http://www.arpansa.gov.au/radiationprotection/basics/xrays.cfm

Vacuum, thermionic emission, high voltage, and a target

Braking radiation CharacteristicX-ray

Auger electrons

v

Target

v0

v1

1121

20 /2/2/ hchmvmvE

v2

2222

21 /2/2/ hchmvmvE

Braking radiation:

x

I

Vemv 2/20

swhchmv /2/ max20

V1

V2

V2 > V1

KL M

Characteristic X-ray

KL M

Auger Electrons

Excitationsource

K

L1

L2

L3

K

L1

L2

L3

CharacteristicsX-Ray photon

k

L1

L2

L3

Augerelectron

Radiativetransition

NonradiativetransitionM} {

K K2 K1

K (L) shell excitation K (L) radiation, etc.

331 LKLKK hhWWh

31

111

LKKK

222 LKLKK hhWWh

22

111;

LKKK

I

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

http://www.antonine-education.co.uk/Pages/Physics_GCSE/Unit_3/Triple_01_X-rays/triple_01.htm

Rotation Anode SourceRotating the anode more cooling time for the part hitby energetic electrons higher power is allowed!

Rotating anode and cooling higher power

  Cr Fe Cu Mo

Z 24 26 29 42

   K1, Å 2.2896 1.9360 1.5405 0.70926

    K2, Å 2.2935 1.9399 1.5443 0.71354

    K, Å 2.2909 1.9373 1.5418 0.71069

  K1 , Å 2.0848 1.7565 1.3922 0.63225

  , filt. V, 0.4mil Mn, 0.4mil Ni, 0.6 mil Nb, 3mils

  , filt. Ti (Z = 22) Cr (Z = 24) Co (Z = 27)

Y (Z = 39)

Resolution, Å 1.15 0.95 0.75 0.35

Critical potential, kV 5.99 7.11 8.98 20.0

Operating conditions, kV: 30-40 35-45 35-45 50-55

Target materials and associated constants

1 mil =0.001 inch = 0.025 mm

Synchrotron radiation source

Lorentz force: )( BvEqF

Electromagnetic radiation produced by relativistic chargedparticles accelerated in circular orbits.

http://www.nsrrc.org.tw/english/lightsource.aspx

http://www.nsrrc.org.tw/english/lightsource.aspx

Undulators ultra-brilliant, single-wavelength radiation from the resulting interference patterns

Absorption:

IdxdI : linear absorption coefficient

)exp(0 xIIdxI

dI I0: X-ray intensity at x = 0

= (/) ; : density;(/): mass absorption coefficient

I0

I

dx

Lambert-Beer law

http://www.helsinki.fi/~serimaa/xray-luento/xray-absorption.html

Reference:

Multicomponent system μ/ρ:For a substance containing several elements

3

33

2

22

1

11 www

wi is the weight fraction of the element i

http://physics.nist.gov/PhysRefData/XrayMassCoef/tab3.html

mm (/): true absorption; (m/): scattering

Small for Z >26

I0

I

Scattering (elastic: same wavelength,Compton scattering: different wavelength )

Fluorescence (longer wavelength)

x

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

Sharp discontinuities at K, LI, LII, LIII, M,… absorption edges!

http://www.helsinki.fi/~serimaa/xray-luento/xray-absorption.html

Use of absorption for filtering function

http://www.helsinki.fi/~serimaa/xray-luento/xray-absorption.html

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

Important aspects of a detector: (1) Losses (2) Efficiency (3) Energy resolution

v

Timev

Time

Random loss(Inevitable)

Serious loss

Losses

v

v

Random losses (always there)

Resolving time of the detector electronic: ts

the maximum rate without losses: 1/ts.Losses as rate .

Quanta Absorbed /second

Qua

nta

Det

ecte

d /s

econ

d

Countingloss

Detector 1

Detector 2 Use filtersNoise?

Efficiency:

fabs,w:

fabs,d: effective excitation ( signals)flosses: counting losses

window

1 1- fabs,w

]1][)1[(production signalfor fraction Effective ,, lossesdabswabs fff

~ 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.

Cou

ntin

g ra

te

Pulse amplitudeV

W

V

WR

R resolution

Resolution

Energy Resolution:

Gas filled detector:Proportional and Geiger counter

RC

Wire anodecathode

X-rays

electron-ion pairs produced:

ie

En E: X-ray energy; ei: effective ionization potential

ei for He, Ar, and Xe: 27.8, 26.4, and 20.8 eV; Using CuK radiation, Ar gas: n = 8040/26.4 = 304

Gain may be defines as

n

NG N: # of electrons reaching wire anode; n: # of electron

produced by X-ray quanta

Typical Gain ~ 104-105.G = 104

Cu radiation on Ar gas filled proportional counter304104 = 3.04106.Typical F 10-10 farad.

V0049.010

106.11004.310

196

C

NeV

Small voltage need further electronic amplification

Bias larger enough (~ several KV) avalanches (G saturated) “Geiger counter” (long deadtime)

Scintillation Counter detector:

http://www.bruker-axs.de/fileadmin/user_upload/xrfintro/sec1_6.html

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

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

Semiconductor detector:

Find more on:http://wwwmayr.informatik.tu-muenchen.de/konferenzen/Jass04/courses/4/Tobias%20Eggert/TalkIoffe.pdf

Excellent energyresolution

Usually coolingis required!

Reasonable countrate

http://144.206.159.178/ft/787/31793/552178.pdf

Si, Ge semiconductor detector (LN2 cooling required )!Spectrometry application!

For spectrometry application without LN2 coolingSi 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.