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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“Elements of X-ray Diffraction”, 3nd Edition, B.D. Cullity,
and S.R. Stock, Prentice Hall, NJ 2001. -- Chapter 1
Rotation anode source
Synchrotron radiation source
Liquid metal jet X-ray source
V2 > V1
K (L) shell excitation K (L) radiation, etc.
Cooling anode Better heat dissipation higher power
(applied potential electron beam current (Typical tube source: 50 kV and 40 mA→2 kW
Rotating the anode more cooling time for the part hit
by energetic electrons higher power is allowed!
Rotating anode and cooling higher power
1 mil =0.001 inch = 0.025 mm
Electromagnetic radiation produced by relativistic charged
particles accelerated in circular orbits.
: linear absorption coefficient
I0: X-ray intensity at x = 0
= (/) ; : density;
(/): mass absorption coefficient
For a substance containing several elements
wi is the weight fraction of the element i
Scattering (elastic: same wavelength,
Compton scattering: different wavelength )
(/): true absorption; (m/): scattering
Small for Z >26
For fluorescent, photoelectron is not necessary as long as the electrons at the ground state are excited to a higher energy level
Proportional Counters ()
(3) Energy resolution
Resolving time of the detector electronic: ts
the maximum rate without losses: 1/ts.
Losses as rate .
Quanta Detected /second
Quanta Absorbed /second
fabs,d: effective excitation ( signals)
flosses: counting losses
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.
Proportional and Geiger counter
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
N: # of electrons reaching wire anode; n: # of electron
produced by X-ray quanta
G = 104
Cu radiation on Ar gas filled proportional counter
304104 = 3.04106.
Typical F10-10 farad.
Small voltage need further electronic amplification
Bias larger enough (~ several KV) avalanches (G saturated)
“Geiger counter” (long deadtime)
Relatively high count rate detector (>100,000 cps is possible)
poor energy resolution
Find more on:
For spectrometry application without LN2 cooling
Si drift detector
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
(4) Inadequate training or violation of procedure
rushing to complete a job,
lack of communication, or
* Everyone should participate the safety training course
offered by the University before actually doing X-ray
or other radiation related experiments.