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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. 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

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:

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


Vacuum, thermionic emission, high voltage, and a target

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

Braking radiation

Characteristic

X-ray

Auger electrons


Braking radiation:

Target

v2

v0

v1

V2 > V1

v

I

V2

V1

x


Characteristic X-ray

K

L

M

Auger Electrons

K

L

M


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.


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


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


Target materials and associated constants

1 mil =0.001 inch = 0.025 mm


Synchrotron radiation source

Lorentz force:

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

Electromagnetic radiation produced by relativistic charged

particles accelerated in circular orbits.


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

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


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


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


Fluorescence (longer wavelength)

I

I0

Scattering (elastic: same wavelength,

Compton scattering: different wavelength )

x

(/): true absorption; (m/): scattering

Small for Z >26


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


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 edges!

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


X-Ray detectors: edges!

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: edges!

(1) Losses

(2) Efficiency

(3) Energy resolution

Losses

v

Time

v

Time

v

Random loss

(Inevitable)

v

Serious loss


Random edges!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


Efficiency: edges!

fabs,w:

fabs,d: effective excitation ( signals)

flosses: counting losses

window

1

1-fabs,w

~ 1


Different detector: different wavelength range to detect! edges!

Efficiency of a 10-cm-long gas ionization chamber as a function of energy, for different gases at normal pressure.


Energy edges!Resolution:

For most of the detectors

Voltage produced  energy

of X-ray quanta.

Counting rate

W

V

Pulse amplitude

Resolution

R resolution 


Gas filled detector: edges!

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


Gain may be defines as edges!

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

produced by X-ray quanta


Typical edges!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)


Scintillation Counter detector: edges!

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


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


Scintillatorhttp://wanda.fiu.edu/teaching/courses/Modern_lab_manual/scintillator.html (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


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

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


Si, http://wanda.fiu.edu/teaching/courses/Modern_lab_manual/scintillator.htmlGe 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


Position sensitive X-Ray detectorhttp://wanda.fiu.edu/teaching/courses/Modern_lab_manual/scintillator.html

Inel


Safety Precautionshttp://wanda.fiu.edu/teaching/courses/Modern_lab_manual/scintillator.html

 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 http://wanda.fiu.edu/teaching/courses/Modern_lab_manual/scintillator.htmlfollow proper procedures has been the result of:

rushing to complete a job,

 fatigue

 illness,

personal problems,

lack of communication, or

 complacency


* Radiological Signshttp://wanda.fiu.edu/teaching/courses/Modern_lab_manual/scintillator.html

* 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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