ChaPtEChaPtER 6: R 6:

ChaPtEChaPtER 6: R 6: X-X-RAYRAY

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

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

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

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

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

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

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

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

BRAGG’S LAWBRAGG’S LAW

MOSELEY’S LAWMOSELEY’S LAW

Henry Moseley

(1887–1915)

Henry Moseley

(1887–1915)

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

MOSELEY’S LAWMOSELEY’S LAW

MOSELEY’S LAWMOSELEY’S LAW

~~ THE END ~~~~ THE END ~~

 “ Life is a succession of lessons, which

must be lived to be understood”

~Ralph Wardo

Emerson~