2. SCOPE OF STUDY
SUB - TOPICS
Discovery &
Qualitative Study
Of Production
Of X-ray
Continuous &
Characteristic Xray Spectra
Mosley’s Law
Diffraction Of
X-ray
Bragg’s Equation
3. INTRODUCTION
DEFINITION OF X-RAY
DEFINITION OF X-RAY
A form of electromagnetic radiation (light) of
A form of electromagnetic radiation (light) of
very short wavelength
very short wavelength
4. DISCOVERY OF PRODUCTION OF
X-RAY
Wilhelm Conrad Roentgen
Wilhelm Conrad Roentgen
(1845 – 1923)
(1845 – 1923)
5. DISCOVERY OF PRODUCTION OF
X-RAY
In 1895, he discovered that when electrons were accelerated by a high voltage in
a vacuum tube and allowed to strike a glass or metal surface inside the tube,
fluorescent minerals some distance away would glow and photographic film would
become exposed.
These effects produced a new type of radiation which was called as x-rays.
His earliest photographic plate from his experiments was a film of his wife,
Bertha's hand with a ring, was produced on Friday, November 8, 1895.
The production of x-rays today is done in a tube using voltages of typically 30
kV to 150kV.
6. DISCOVERY OF PRODUCTION OF
X-RAY
A film of his wife, Bertha's hand with aaring
A film of his wife, Bertha's hand with ring
X-rays can be produced by aa high-speed
X-rays can be produced by
high-speed
collision between an electron and aa
collision between an electron and
proton.
proton.
7. DISCOVERY OF PRODUCTION OF
X-RAY
When charged particles collide, they produce bundles of energy called photons
that fly away from the scene of the accident at the speed of light.
Since electrons are the lightest known charged particle, they are most fidgety, so
they are responsible for most of the photons produced in the universe.
Energies of X-ray photons range from hundreds to thousands of times higher
than that of optical photons.
Optical photons is the only photons perceived by the human eye.
8. DISCOVERY OF PRODUCTION OF
X-RAY
Speed of the particles when they collide or vibrate sets a limit on the energy of
the photon.
Speed is also a measure of temperature.
On a hot day, the particles in the air are moving faster than on a cold day.
At very high temperatures (millions of degrees Celsius) produce X-rays.
9. DISCOVERY OF PRODUCTION OF
X-RAY
The Electromagnetic Spectrum. The wavelength of radiation
The Electromagnetic Spectrum. The wavelength of radiation
produced by an object is usually related to its temperature.
produced by an object is usually related to its temperature.
11. PRODUCTION OF X-RAY
Electrical current is run
Electrical current is run
through
through
the
the
tungsten
tungsten
filament, causing it to glow
filament, causing it to glow
and emit electrons.
and emit electrons.
(Production of X-ray)
(Production of X-ray)
The X-rays then move
The X-rays then move
through aa window in the
through window in the
X-ray tube and can be
X-ray tube and can be
used
to
provide
used
to
provide
information
information
A large voltage difference (kV) is
A large voltage difference (kV) is
placed between the cathode and the
placed between the cathode and the
anode, causing the electrons to
anode, causing the electrons to
move at high velocity from the
move at high velocity from the
filament to the anode target. .
filament to the anode target
Upon striking the atoms in the target,
Upon striking the atoms in the target,
the electrons dislodge inner shell
the electrons dislodge inner shell
electrons resulting in outer shell
electrons resulting in outer shell
electrons having to jump to aa lower
electrons having to jump to
lower
energy shell to replace the dislodged
energy shell to replace the dislodged
electrons.
electrons.
12. QUALITATIVE STUDY OF
PRODUCTION OF X-RAY
MEDICAL
Track the
broken bones,
destroy the
cancer cells ,
investigate the
organs in the
body
RESEARCH
Study the crystal
structures and
separation distance
of atoms
INDUSTRY
Contribution
Contribution
Check the cracks
in structure of
plastic, track the
defects in
machine or
engine
General
Check the goods and
luggage at airport
13. CONTINUOUS & CHARACTERISTIC
OF X-RAY SPECTRA
DEFINITION OF CONTINUOUS
DEFINITION OF CONTINUOUS
X-RAY SPECTRA
X-RAY SPECTRA
When the target material of the X-ray tube is bombarded with
When the target material of the X-ray tube is bombarded with
electrons accelerated from the cathode filament, two types of
electrons accelerated from the cathode filament, two types of
X-ray spectra are produced.
X-ray spectra are produced.
14. CONTINUOUS & CHARACTERISTIC
OF X-RAY SPECTRA
The continuous spectra consists of a range of wavelengths of X-rays with
minimum wavelength and intensity (measured in counts per second) dependent on
the target material and the voltage across the X-ray tube.
Minimum wavelength decreases and the intensity increases as voltage increases.
The second type of spectra, called the characteristic spectra, is produced at high
voltage as a result of specific electronic transitions that take place within individual
atoms of the target material.
16. CONTINUOUS & CHARACTERISTIC
OF X-RAY SPECTRA
The easiest to see using the simple Bohr model of the atom.
In such a model, the nucleus of the atom containing the protons and neutrons is
surrounded by shells of electrons.
The innermost shell, called the K- shell, is surrounded by the L- and M - shells.
When the energy of the electrons accelerated toward the target becomes high
enough to dislodge K- shell electrons, electrons from the L - and M - shells move
in to take the place of those dislodged.
18. CONTINUOUS & CHARACTERISTIC
OF X-RAY SPECTRA
Each of these electronic transitions produces an X-ray with a wavelength that
depends on the exact structure of the atom being bombarded.
A transition from the L - shell to the K- shell produces a Kα X-ray, while the
transition from an M - shell to the K- shell produces a K β X-ray.
These characteristic X-rays have a much higher intensity than those produced by
the continuous spectra, with Kα X-rays having higher intensity than Kβ X-rays.
20. CONTINUOUS & CHARACTERISTIC
OF X-RAY SPECTRA
The wavelength of these characteristic x-rays is different for each atom in the
periodic table (of course only those elements with higher atomic number have Land M - shell electrons that can undergo transitions to produce X-rays).
A filter is generally used to filter out the lower intensity K β X-rays.
22. DIFFRACTION OF X-RAY
CONSTRUCTIVE INTERFERENCE
Since a beam of X-rays consists of a bundle of separate waves, the waves
can interact with one another. If all the waves in the bundle are in phase,
that is their crests and troughs occur at exactly the same position (the same
as being an integer number of wavelengths out of phase, nλ, n = 1, 2, 3, 4,
etc.), the waves will interfere with one another and their amplitudes will
add together to produce a resultant wave that is has a higher amplitude (the
sum of all the waves that are in phase.
24. DIFFRACTION OF X-RAY
DESTRUCTIVE INTERFERENCE
If the waves are out of phase, being off by a non-integer number of
wavelengths, then destructive interference will occur and the amplitude
of the waves will be reduced. In an extreme case, if the waves are out of
phase by an odd multiple of 1/2l [(2n+1)/2l ], the resultant wave will
have no amplitude and thus be completely destroyed.
26. DIFFRACTION OF X-RAY
The atoms in crystals interact with X-ray waves in such a way as to produce
interference.
The interaction can be thought of as if the atoms in a crystal structure reflect the
waves.
But, because a crystal structure consists of an orderly arrangement of atoms, the
reflections occur from what appears to be planes of atoms.
27. DIFFRACTION OF X-RAY
X-rays can be diffracted from many possible planes within aacrystal
X-rays can be diffracted from many possible planes within crystal
28. BRAGG’S LAW
How it happens ??
Lets imagine a beam of X-rays entering a crystal with one of these planes of
atoms oriented at an angle of θ to the incoming beam of monochromatic X-rays.
Two such X-rays are shown here, where the spacing between the atomic planes
occurs over the distance, d.
Ray 1 reflects off of the upper atomic plane at an angle θ equal to its angle of
incidence.
Similarly, Ray 2 reflects off the lower atomic plane at the same angle θ.
30. BRAGG’S LAW
While Ray 2 is in the crystal, however, it travels a distance of 2a farther than
Ray 1.
If this distance 2a is equal to an integral number of wavelengths (nλ), then Rays
1 and 2 will be in phase on their exit from the crystal and constructive interference
will occur.
31. BRAGG’S LAW
How to prove ??
If the distance 2a is not an integral number of wavelengths, then destructive
interference will occur and the waves will not be as strong as when they entered the
crystal.
Thus, the condition for constructive interference to occur is
nλ = 2a
nλ = 2a
32. BRAGG’S LAW
But from trigonometry, we can figure out what the distance 2a is in terms of the
spacing, d, between the atomic planes.
a = d sin θ
a = d sin θ
or 2a = 2 d sin θ
or 2a = 2 d sin θ
nλ = 2d sin θ
nλ = 2d sin θ
Bragg's Law
Bragg's Law
35. MOSELEY’S LAW
Moseley's Law describes the relationship
Moseley's Law describes the relationship
between atomic number and wavelength of a
between atomic number and wavelength of a
spectral line
spectral line
36. MOSELEY’S LAW
The constant σ (sigma) is equal to 1 for the K-lines
and 7.4 for the more shielded L-lines. For energy this
expression is approximately equivalent to
