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:
mv 0 / 2  e  V
2
 E  mv 1 / 2  mv 2 / 2  h  2  hc /  2
2
Target
2
v2
v0
v1
 E  mv 0 / 2  mv 1 / 2  h  1  hc / 1
2
2
V2 > V1
v
I
V2
V1
x
mv / 2  h  max  hc /  sw
2
0

Characteristic X-ray
K
L
M
Auger Electrons
K
L
M
Nonradiative
transition
Auger
Characteristics
electron
X-Ray photon
L3
L3
L2
L2
L1
L1
} M{
L3
L2
L1
Excitation
source
K
K2
K1 Radiative
K
K transition
K (L) shell excitation  K (L) radiation, etc.
h K 1  W K  W L 3  h K  h L 3
h K 2  W K  W L 2  h K  h L 2

1
 K

1
1
K

1
K
;
L3
1
 K

2
1
K

1
K
L2
k
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.antonineeducation.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
Cr
Fe
Cu
Mo
24
26
29
42
K1, Å
2.2896
1.9360
1.5405
0.70926
K2, Å
2.2935
1.9399
1.5443
0.71354
K, Å
2.2909
1.9373
1.5418
0.71069
K1 , Å
2.0848
1.7565
1.3922
0.63225
 , filt.
, filt.
V, 0.4mil
Z
Mn, 0.4mil Ni, 0.6 mil
Nb, 3mils
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
1 mil =0.001 inch = 0.025 mm
Synchrotron radiation source
Lorentz force:

  
F  q( E  v  B )
http://www.nsrrc.org.tw/en
glish/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/en
glish/lightsource.aspx
Absorption:
Lambert-Beer law
Reference:
http://www.helsinki.fi/~s
erimaa/xray-luento/xrayabsorption.html
I
I0
dx
 dI  Idx : linear absorption coefficient
dI
  dx  I  I 0 exp( x) I0: X-ray intensity at x = 0
I
 = (/) ;  : density;
(/): mass absorption coefficient
Multicomponent system μ/ρ:
For a substance containing several elements
 w11 w2 2 w3 3





1
2
3
wi is the weight fraction of the element i
http://physics.nist.gov/PhysRefData/XrayMassCoef/tab3.html
Fluorescence (longer wavelength)
I
I0
x
m   m
 
  
Scattering (elastic: same wavelength,
Compton scattering: different wavelength )
(/): true absorption; (m/): scattering
Small for Z >26
True absorption:
http://www.helsinki
.fi/~serimaa/xrayluento/xrayabsorption.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/xrayluento/xrayabsorption.html
Use of absorption for filtering function
http://www.helsinki
.fi/~serimaa/xrayluento/xrayabsorption.html
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
Important aspects of a detector:
(1) Losses
(2) Efficiency
(3) Energy resolution
Losses
v
Time
v
Time
v
v
Random loss
(Inevitable)
Serious loss
Quanta Detected /second
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
Detector 1
Quanta Absorbed /second
Use filters
Noise?
Efficiency:
window
fabs,w:
1
1- fabs,w
fabs,d: effective excitation ( signals)
flosses: counting losses
Effective
fraction
for signal production
 [( 1  f abs , w ) f abs , d ][ 1  f losses ]
~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.
Counting rate
Energy Resolution:
For most of the detectors
Voltage produced  energy
of X-ray quanta.
Resolution R  W
V
R   resolution 
W
V
Pulse amplitude
Gas filled detector:
Proportional and Geiger counter
cathode Wire anode
X-rays
R
electron-ion pairs produced:
E
n
E: X-ray energy; ei: effective ionization potential
ei
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
C
Gain may be defines as
N
G
n
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 counter
304104 = 3.04106.
Typical F 10-10 farad.
Ne 3.04 106 1.6 10 19
V

 0.0049V
10
C
10
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/scin
tillator.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:
Excellent energy
resolution
Usually cooling
is required!
Reasonable count
rate
Find more on:
http://wwwmayr.informatik.tumuenchen.de/konferenzen/Jass04/courses/4/Tobias%20Eggert/TalkIoffe.pdf
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
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.