chapter 6 x ray
TRANSCRIPT
SCOPE OF STUDYSCOPE OF STUDYSUB - TOPICSSUB - TOPICS
Discovery & Discovery & Qualitative Study Qualitative Study
Of Production Of Production Of X-ray Of X-ray
Diffraction Of Diffraction Of X-ray X-ray
Mosley’s LawMosley’s Law
Bragg’s EquationBragg’s EquationContinuous & Continuous &
Characteristic X-Characteristic X-ray Spectra ray Spectra
INTRODUCTIONINTRODUCTION
DEFINITION OF X-RAYDEFINITION OF X-RAY
A form of electromagnetic radiation (light) of
very short wavelength
A form of electromagnetic radiation (light) of
very short wavelength
DISCOVERY OF DISCOVERY OF PRODUCTION OF X-PRODUCTION OF X-
RAYRAY
Wilhelm Conrad Roentgen
(1845 – 1923)
Wilhelm Conrad Roentgen
(1845 – 1923)
DISCOVERY OF DISCOVERY OF PRODUCTION OF X-PRODUCTION OF X-
RAYRAY 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.
DISCOVERY OF DISCOVERY OF PRODUCTION OF X-PRODUCTION OF X-
RAYRAY
X-rays can be produced by a high-speed
collision between an electron and a
proton.
X-rays can be produced by a high-speed
collision between an electron and a
proton.
A film of his wife, Bertha's hand with a ringA film of his wife, Bertha's hand with a ring
DISCOVERY OF DISCOVERY OF PRODUCTION OF X-PRODUCTION OF X-
RAYRAY 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.
DISCOVERY OF DISCOVERY OF PRODUCTION OF X-PRODUCTION OF X-
RAYRAY
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.
DISCOVERY OF DISCOVERY OF PRODUCTION OF X-PRODUCTION OF X-
RAYRAY
The Electromagnetic Spectrum. The wavelength of radiation
produced by an object is usually related to its temperature.
The Electromagnetic Spectrum. The wavelength of radiation
produced by an object is usually related to its temperature.
PRODUCTION OF X-PRODUCTION OF X-RAYRAY
Electrical current is run
through the tungsten
filament, causing it to glow
and emit electrons.
Electrical current is run
through the tungsten
filament, causing it to glow
and emit electrons.
A large voltage difference (kV) is placed between the cathode and the anode, causing the electrons to move at high velocity from the filament to the anode target.
A large voltage difference (kV) is placed between the cathode and the anode, causing the electrons to move at high velocity from the filament to the anode target.
Upon striking the atoms in the target, the electrons dislodge inner shell electrons resulting in outer shell electrons having to jump to a lower energy shell to replace the dislodged electrons.
Upon striking the atoms in the target, the electrons dislodge inner shell electrons resulting in outer shell electrons having to jump to a lower energy shell to replace the dislodged electrons.
(Production of X-ray)The X-rays then move through a window in the X-ray tube and can be used to provide information
(Production of X-ray)The X-rays then move through a window in the X-ray tube and can be used to provide information
QUALITATIVE STUDY QUALITATIVE STUDY OF PRODUCTION OF X-OF PRODUCTION OF X-
RAYRAY
ContributionContribution
MEDICAL
Track the broken bones,
destroy the cancer cells ,
investigate the organs in the
body
INDUSTRY
Check the cracks in structure of
plastic, track the defects in
machine or engine
RESEARCH
Study the crystal structures and
separation distance of atoms
General
Check the goods and luggage at airport
CONTINUOUS & CONTINUOUS & CHARACTERISTIC OF X-CHARACTERISTIC OF X-
RAY SPECTRARAY SPECTRA
DEFINITION OF CONTINUOUS
X-RAY SPECTRA
DEFINITION OF CONTINUOUS
X-RAY SPECTRA
When the target material of the X-ray tube is bombarded with
electrons accelerated from the cathode filament, two types of
X-ray spectra are produced.
When the target material of the X-ray tube is bombarded with
electrons accelerated from the cathode filament, two types of
X-ray spectra are produced.
CONTINUOUS & CONTINUOUS & CHARACTERISTIC OF X-CHARACTERISTIC OF X-
RAY SPECTRARAY 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.
CONTINUOUS & CONTINUOUS & CHARACTERISTIC OF X-CHARACTERISTIC OF X-
RAY SPECTRARAY 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.
CONTINUOUS & CONTINUOUS & CHARACTERISTIC OF X-CHARACTERISTIC OF X-
RAY SPECTRARAY 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.
CONTINUOUS & CONTINUOUS & CHARACTERISTIC OF X-CHARACTERISTIC OF X-
RAY SPECTRARAY 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 L-
and M - shell electrons that can undergo transitions to produce X-rays).
A filter is generally used to filter out the lower intensity Kβ X-rays.
DIFFRACTION OF X-DIFFRACTION OF X-RAYRAY
DEFINITION
OF
DIFFRACTION
DEFINITION
OF
DIFFRACTION
The light bends around objects it passes and spreads out after
passing through narrow slits. It gives diffraction patterns due to
interference between rays of light that travel different distances.
DIFFRACTION OF X-DIFFRACTION OF X-RAYRAY
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.
CONSTRUCTIVE INTERFERENCE
DIFFRACTION OF X-DIFFRACTION OF X-RAYRAY
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.
DIFFRACTION OF X-DIFFRACTION OF X-RAYRAY
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.
DIFFRACTION OF X-DIFFRACTION OF X-RAYRAY
X-rays can be diffracted from many possible planes within a crystalX-rays can be diffracted from many possible planes within a crystal
BRAGG’S LAWBRAGG’S LAW
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.
How it happens ??
BRAGG’S LAWBRAGG’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.
BRAGG’S LAWBRAGG’S LAWHow 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 = 2anλ = 2a
BRAGG’S LAWBRAGG’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
or 2a = 2 d sin θ
nλ = 2d sin θ
a = d sin θ
or 2a = 2 d sin θ
nλ = 2d sin θ Bragg's LawBragg's Law
MOSELEY’S LAWMOSELEY’S LAW
Moseley's Law describes the relationship
between atomic number and wavelength of a
spectral line
Moseley's Law describes the relationship
between atomic number and wavelength of a
spectral line
MOSELEY’S LAWMOSELEY’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