electromagnectic spectrum and properties of x -rays
Types of radiation comprising ES
Properties of X rays
Energy is defined as ability to do work.
There are different types of energy:
KINECTIC ENERGY: it is energy produced
by virtue of movement.
POTENTIAL ENERGY: produced by virtue
of its position ex: coiled spring.
HEAT ENERGY: it is movement of
molecules and atoms of any material.
The level of heat is indicated by
ELECTRICAL ENERGY: it is measured by
multiplying the electric charge being
moved by electrical force.
CHEMICAL ENERGY: it is that energy
locked up in the chemical compounds
and released under certain
circumstances eg explosives
NUCLEAR ENERGY: it is that energy that is
locked up in the heart of the nucleus of an
atom also called, atomic energy.
RADIATION ENERGY: it is that energy
which is released during the process of
ionization or excitation of an atom.
RADIATION: it is defined as the emission
and propagation of energy through space or
substances in form of waves or particles.
RADIOACTIVITY: it is the process by
which certain unstable atoms or elements
undergo spontaneous disintegration or
decay, in an effort to attain a more balanced
X rays belong to a group of radiation known
as electromagnetic radiation.
Electromagnetic radiation is the transport
of energy through space as a combination of
electric and magnetic fields.
Electromagnetic radiation is produced by a
charged particle being accelerated.
The converse is also true, that is, a charge
being accelerated will emit EM radiation.
EM radiation is made up of an electric and a
magnetic field that mutually supports each
EM radiation propagates in the form of
They may be compared to waves travelling
down a stretched rope when one end is
moved up and down in a rhythmic motion.
EM radiation do not need any medium and
can propagate in vacuum.
Waves of all type have an associated
wavelength and frequency.
The distance between the two successive
crests or troughs is the wave length and is
denoted by λ (Greek letter lambda, the
initial for length).
The number of waves passing through a
particular point in a unit time is the
frequency, denoted by “ν” (the Greek letter
“nu”, the initial for number.
If each wave has a length λ, and ν waves pass
a given point in unit time, the velocity of the
wave is given by:
V= λ × ν
EM radiations travel with the velocity of
light ie 186,000 miles per second.
Therefore c= λ × ν
c is velocity of light
c= λ × ν
Because all types of radiation have the same
velocity, frequency of the radiation must be
inversely proportional to the wavelength.
All types of radiation in the spectrum differ
basically in the wavelength.
The various parts of the spectrum are
named according to the manner in which
the type of radiation is generated or
There is considerable overlap in the
wavelengths of various members of the
X-rays are considered useful when their energy
level is matched to the task of interest
Of the total amount of x-rays produced, only x-
rays of certain energy levels are useful to
diagnostic image production, these x-rays fall
into the diagnostic energy range
X-rays used in dentistry have a wavelength of
0.1 to 0.5Å
Short EM waves, such as X rays, may react
with matter as if they were particle rather
These particles are actually discrete bundles
of energy and each of these bundles of
energy is calles a quantum or photon.
The amount of energy carried by each
photon or quantum depends on frequency
of the radiation.
If the frequency is doubled, the energy of
the photons is doubled.
The actual amount of energy can be
calculated by multiplying its frequency by a
E= hν ( h= Planck’s Constant)
The constant has been determined
experimentally to be 4.13 × 10-18 KeV sec and
is called the Planck’s Constant
In SI unit it is 6.62 ×10-34 Joules sec.
The particle concept is used to describe the
interactions between radiation and matter.
The EM spectrum is the ENTIRE range of
EM waves in order of increasing frequency
and decreasing wavelength.
HERTZIAN WAVES: these waves are used by
high altitude transmission satellites, and
have wavelength of 1016 to 1013 Å.
These waves can pass through most
materials except that of great bulk.
Wavelength varies from 1013 to 108 Å.
MEDICINE: radiowaves are used to transmit
the pattern of the heartbeat through a
OTHERS: to convey information from one
place to another through media(air, space).
Wavelength: 3×10-2m to 3×10-4 , these
overlap the wavelength of communication
waves on one end and infrared on other
Transmit information to satellite.
These waves can penetrate tissues and cause
moisturized molecules in cell to vibrate
resulting in internal friction and increase in
temperature of affected cell.
In selected cases of cancer therapy.
In oral surgery, to reduce postoperative
swelling and trismus arising from traumatic
The name infrared means “below the red”.
These have wavelength ranging from 40,000
to 1,00,000 Å
These occupy the part of spectrum with a
frequency less than that of visible light and
greater than that of radio waves.
These were discovered in 1800 by Sir
To study cloud structure.
The temperature of a distant object can be
determined by analysis of infrared radiation
from the object.
Radiometers operating in the infrared range
serve as the basis for many instruments,
including heat seeking devices in missiles
and devices for spotting and photographic
persons in the dark or fog.
Medical uses include technique of thermal
imaging of thermography.
In dentistry: it is used for tooth vitality
testing, surgical diathermy, altering
properties of dental materials like waxes,
gutta percha and for curing acrylic.
Wavelength ranges from 4,000 to 7700Å.
The range of colour is often called “VIBGYOR”,
with red having the longest wavelength and violet
having shortest wavelength.
Red, orange, yellow, green, blue, indigo, violet.
In optical fibers.
In dentistry it is used in dental photography
and operative field illumination.
Wavelength ranges from 1,000 to 2,000Å.
These rays have slight penetrating power
and can penetrate live tissues for a depth of
few mm and cause biological effects like:
Photo chemical cornification of skin and
skin carcinoma (malignant dermal
Aging of skin.
Eyes are sensitive to UV rays which can
cause cataract or keratitis.
Is an agent in the production of vitamin D.
The UV rays can be divided into 3
Between 200 and 290 nm, short or
germicidal UV rays or UVC, these can cause
genetic mutations, altered reproductive
cycles and cell death.
Between 290 and 320 middle or erythemal
UV rays or UVB, these can cause skin
erythema and are commercially available as
sun or mercury vapor lamps.
Between 320 and 380 nm , long or black
light UV rays or UVA, on its own it is not
damaging but when used with sensitizing
chemicals, it can cause extensive biological
Photo polymerization of composite used
Placing pontic in temporary bridge work
Grenz or super soft X rays: 1-2 Å, mainly
used to treat superficial lesions
Soft X rays: 1-0.5 Å, used in contact therapy.
Medium: 0.5-0.1 Å, mainly used in
diagnostic and superficial therapy.
Hard X rays: 0.1 Å , mainly used for deep X
Its properties of fluorescence is used in
medicine for fluoroscopic examination and
intensifying screens in extra oral
Radiography and monitoring film badges.
To sterilize commercial items in bulk.
They are high powered X rays, having wave
length of 0.001 Å.
These are EM radiations, but there source is
from radioactive decay process.
They have shorter wavelength and greater
penetrating power and are used in
treatment of tumors ex: Radon needles or
seeds that are implanted at the tumor site,
percutaneous radiotantalum wire implants.
These have the shortest wavelength of
They played a critical role in the scientific
study of atomic nucleus and its
Light amplification by stimulated emission
of radiation is a device which can operate in
infrared, visible or UV region of the
spectrum and which amplifies
electromagnetic waves by stimulated
emission of radiation.
When atoms or molecules absorb energy
they can emit light spontaneously or they
can be stimulated to do so by a light wave.
If a body of atoms is raised to excited state
by pumping, then an incident light wave will
simulate photon emission and net
amplification of the incident light beam
The output is extremely powerful and
mobilizes intense heat at close range to emit
photons at an infinitely greater rate than
LASER light has four characteristics that
distinguish it from light produced by other
sources. These are:
Laser light is highly directional and travels in a
narrow beam, the sides of which stay almost
Lasers produces coherent light, that is it has
only one frequency.
It is of one single color.
It is very bright, powerful with very high
Laser concentrates and amplifies the light to
a given concentrated beam of energy which
can melt metals and drill holes in them.
It can be used to make very accurate
measurement of distance, perform delicate
surgical procedure involving the eye.
They have replaced many conventional
techniques which have lead to shorter
period of treatment.
It has also reduced blood loss due to its
ability to seal blood vessels, less post
operative infection and the fact that
difficult, often inaccessible regions of the
body can be reached more easily.
In dentistry two types of lasers are used:
Soft tissue laser (800-900 nm): eg. Argon,
Hard tissue laser (2500-3000nm): eg Er:
YAG dental laser.
Surgical excision of benign tumors and
small soft tissue growths (eg: epulis)
Low intensity lasers to reduce pain
Treatment of TMJ for reduction of pain and
X rays are weightless packages of pure
energy that are without electrical charge
and that travel in waves along a straight line
with a specific frequency or speed.
The properties of X rays can be classified
Wavelength 10-0.01 Å.
They travel through space in a wave motion.
In free space they travel in a straight line.
They travel in speed of light (186000 miles
As they travel through space, they can
produce an electric field at right angle to
their path of propagation and a magnetic
field to right angle to electric field.
They are invisible to eye and can not be seen,
heard or smelt.
They can not be focused by a lens.
They can not be reflected, refracted or
deflected by a magnet or electric field as they
do not possess any charge.
They do not require any medium for
They are pure energy, no mass and they
transfer energy from place to place in the form
of quanta (photon)
In free space they obey the inverse square
law, which states that for a point source of
radiation the intensity (I) at any given place
varies inversely as the square of distance
from the source to the place at which
intensity is being considered.
I∞i/d2 or I =k/d2
K is a constant.
X rays are produced by collision of electrons
by tungsten atoms.
Collision can be of two types:
Continuous spectra (general radiation,
Bremsstrahlung Radiation, Braking
Characteristic spectrum or line spectrum
Also called as brems, white, or general radiation.
Derived from two German words: bremse- ‘brake’ &
Called as ‘braking radiation’ as the radiation is
produced by ‘braking’ or deceleration of high speed
A cathode electron that completely avoids the
orbital electrons may come sufficiently close to the
nucleus to come under its influence.
The incoming electron penetrates
the outer electron shell and passes
close to the nucleus of the
The incoming electron is slowed
down and deflected by the nucleus
with a large loss of energy, which is
emitted in the form of X rays.
The amount of deceleration and
degree of deflection determines
the amount of energy lost by the
bombarding electron and hence
the energy of the resultant emitted
photon has a wide range of
spectrum of energies and therefore
called CONTINIOUS SPECTRUM.
The incoming electron collides with an
inner shell tungsten electron, displacing it
to outer shell (excitation), or displacing it
from the atom (ionization), with a large
loss of energy and subsequently the
orbiting tungsten electros rearrange
themselves to return the atom to neutral
or ground state.
This involves electron jumps which results
in the emission of X ray photons with a
specific energy called CHARACTERISTIC
Generation of photons with a wide range of
photon energies (continuous spectrum)
This is due to :
a) Continuously varying voltage difference
between target & filament
b) Most electrons participate in many
interactions before losing their energy
X rays can penetrate various objects and
degree of penetration depends upon:
Quality (penetration power), is defined as
the energy carried by the X ray beam.
Quality is determined by KV, milli
amperage, distance between the target and
the object, time of exposure, filtration and
Property of attenuation, absorption, scatter
when passing through matter the intensity
of radiation is reduced (attenuation) both
because radiation energy is taken up by the
material (absorption) and some is deflected
from the original path to travel in a new
Components of the body arranged in order of
their power to absorb X rays, starting from
Soft tissue, blood, body fluids
Dentin and cementum
When x-ray photons arrive at patient:
a. Some x-rays are merely scattered with no loss
b. Some x-ray photons are absorbed completely
in the patient (total loss of energy), &
c. Some x-ray photons pass through the patient
without interacting with the tissue atoms
d. Some x-ray photons are scattered after loss of
In the case of diagnostic X ray beam there
are three mechanisms by which these
processes take place:
It is a process by which radiation is
deflected without losing energy.
X rays when passing close to an atom causes
the bound electrons to vibrate momentarily
at a frequency equal to that of incident
The incident photon then ceases to exit.
The vibration causes the electron to radiate energy
in the form of another X ray photon of the same
frequency and energy as that in the incident beam.
Usually the secondary photon emitted is at an angle
to the path of incidental X ray.
Contributes to 8% of the total no. of
Is of little importance in radiography as the
it involves low energy x-rays.
At energy levels employed in diagnostic
radiology, the effect of coherent scattering is
negligible in production of fog.
This property is used to investigate internal
molecular structure of materials by method
of X ray diffraction, called X ray
It is a process of interaction of the incident photon ant the bound electron
leading to emission of characteristic radiation.
It occurs when an incident photon collides with a bound electron in the atom of
the absorbing medium.
The incident photon ceases to exit and its energy helps to eject a bound
electron from its shell to become a recoil electron or a photo electron.
The kinetic energy imparted to the recoil electron is equal to the energy of the
incident photon minus that required to overcome the electron binding energy.
The orbital vacancy caused by the electron reshuffle and the neutrality is obtained
by attracting an electron from outside.
During this rearrangement characteristic radiation is emitted.
In diagnostic radiography the characteristic
radiation generated is of no significance as
the X ray photons which are absorbed by the
patient are of low energy.
Or inelastic scattering is an interaction of
photons with free or loosely bound outer
The photon gives some of its energy to the electron and it, itself continues
in a new direction, but with reduced energy and hence with increased
The ejected outer shell electron is called compton or recoil electron.
If scattered through a small angle, very
small amount of energy is lost to the outer
The recoil electrons further ionizing
interactions with the tissues, and gradually
lose energy along their tracts by causing
secondary radiations and consequent
This creates a serious problem as photons
that are scattered at narrow angles have an
excellent chance of reaching the film &
producing film fog.
Contributes to 62% of the x-ray scattering.
Due to their energy, rays can emit
photoelectrons from metals, when allowed
to fall on them.
HEATING EFFECT: the production of heat
is due to slowing down of the primary
electrons, it also arises as an end product of
the chemical reactions induced by
FLUORESCENCE: when X rays fall upon
certain material, visible light is emitted
IONIZATION: this is a process of converting
atoms into ions.
The outer electron of the atoms play an
important role in chemical combinations
and therefore any disturbance in the outer
electron configuration of an atom brings
about chemical changes.
X rays induces color changes in several
Methylene blue gets bleached
Sodium platinocyanide which is apple green
turns to darker shades then light brown and
finally dark brown.
Brings about molecular changes in
Organic compound gets oxidized to carbon
dioxide with release of hydrogen.
Water in organic substances undergo
oxidation and reduction reactions when
X rays can cause oxidation of ferrous
sulphate to ferric sulphate and this is used
as a method of measuring X ray dosage
X rays can cause destruction of the
fermentation power of enzymes, which are
vital substances for metabolism of cells of
all living materials.
When X rays are incident on an atom, one of
the reaction it produces is excitation. this
property is used in:
Treatment of malignant lesions.
Germicidal or bactericidal effect and are
used for sterilization and preservation of
Effects can be of two types:
The effect is cumulative and depends upon
the type of tissues and intensity of the
It may range from simple sun burn to severe
This is due to radiation induced mutation of
genes and chromosomes.
These are usually seen in off springs of
The fetus is more sensitive to radiation in
early stages of development.
Photographic film when exposed to X rays
and developed will turn black.
This blackening is known as film density.
Diagnostic use in dentistry and medicine.
Medico legal cases.
Used to destroy malignant cells and cure
Alteration of cells and tissues for
Oral Radiology Principles and
Interpretation, 2nd Edition, Gaoz and White.
Oral Radiology, Principles and
Interpretation, 4th Edition, White and
Christinsen’s Introduction to the Physics of
Diagnostic Radiology, 3rd Edition, by
Currary T.S., J.E. Dowdry, R.C. Murry.
Eric Whaites: Essential of Radiology and
Radiography, 2nd Edition.