Presented by DR VAIBHAV SALUNKE
1st YEAR PG
Guided by DR JYOTSNA PATEL
on the night of 8th nov.1895 by prof.wilhelm
conrad roentgen who was a professor of physics at
the university of wurtzberg,germany,accidently
discovered x-rays. He was experimenting with
hittrof-crookstube for cathode rays,when he
Wilhelm Conrad Roentgen
Observed greenish glow emanating from barium
platinocynide screen kept at a distance. when he interpose
his hand unintentionally between the tube and screen he
could detect the image of his bones in the shadow. He at
once realized the significance of this finding and
established the property of penetration. he then covered the
tube with black paper and florescent persisted which
further confirms the property of penetration.
Roentgen has discovered these new rays and as
anything unknown in maths is disignated by symbol
X called then X-rays
The first x-ray
Bertha’s hand .
Unit of measurement in x-ray region is Å and nm.
1 Å = 10-10 m, 1 nm = 10 Å = 10-9 m
X-ray wavelengths are in the range 10-0.01 Å.
Wavelength of visible light ~ 6000 Å.
X-rays are electromagnetic radiation of exactly the same nature
as light but of very much shorter wavelength
• Electromagnetic radiation → can be defined as
propagation of wave like energy (witout mass) through
space or matter .
According to the classical
theory (wave theory)
can be considered as wave
According to the quantum
radiation can also be
considered as a particles
•All EM radiations travel with the speed of light
186000miles/sec, 3×10ˆ8 m/sec but they differ in wavelength
•Wavelength (λ) – distance between 2 successive crests / trough
•Frequency (ν) – number of crests /cycle per second (Hz)
• (λ) wavelength ↓ (ν) frequency ↑
•EM travel with the speed of light c , c=λν
•Wave concept of EMR explains why radiation may be reflected ,
refracted, diffracted and polarized .
If each wave has length λ and ν waves pass a given point in
velocity of wave is v = λ× ν
•Short EM waves like XRAYS react with matter as if they are
particles rather than waves.
•These particles are discrete bundles of energy and each bundle is
called quantum /photon.
•Photon travel at the speed of light.
•Amount of energy carried by each photon depends on frequency of
•If frequency doubled energy doubled .
•Particle concept can explain the interaction with matter like
photoelectric and Compton effect .
Energy calculated E=hν
h= Planck's constant (4.13×10 ˆ-18 Kev sec )
Relationship between wavelength and frequency
c – velocity of light (~3×108 m/s)
also E= hν
Instead of ν
E =hc/λ ( h×c = 1.24)
•Energy of photon =ev
•X-ray measured in kilo ev , 1Kev = 1000 ev
The heart of x ray machine is made of x ray
tube and its power supply.
Principally composed of 2 parts 1. filament 2.focusing
Filament made of tungsten wire 0.2 mm diameter coiled to
form a vertical spiral 0.2 cm diameter and 1 cm length
1. high atomic no. (Z=74) more electrons
are given out i.e high thermionic emission
2. high melting point(3380 c ) so that
filament should not melt 3. low vapor
pressure at high temperature so that it will
not vaporize 4. Thin wire 5. Long life
When Current flows – wire heated
Absorbs thermal energy – electrons move a small
distance from the surface of metal
This escape is referred to as thermionic
Emission of electrons resulting from the absorption
of thermal energy – thermionic emission
Electron cloud surrounding the filament produced
by thermionic emission is termed “Edison effect”
Anode is in the form of
copper disc 7.5 – 10
cm in diameter focal
spot is in the form of
0.6 mm ring
copper disc During
exposure the copper
disc is rotated so that
at each time different
focal spot get
The actual focal spot size is 1X 3mm however the anode is
angled at 20 degree to x ray beam this causes the effective
focal spot to be 1X1 mm . So that rectangular focal spot
appeare as square this is done to facilitate the following :-1.
heat distribution across larger surface at the anode at the
same time. 2.sharp image because because rectangular focal
spot appears as square when viewed in the direction of the
central ray (smaller the focal spot sharper the image )
Intensity of beam
depends on the angle
at which the x-rays
are emitted from the
exposure on anode
side < cathode
Heel effect is less
with smaller films
1. diagnostic properties
B. Photographic properties
A . Direct effect
B . Indirect effect
3. Thermal properties
4. Chemical properties
X rays are ionising raditation ,they can cause alteration
in the chemical through which they pass .fecl 2 to
fecl3 and H2O to H+ and OH-.
5. Properties of physics
1. X rays are invisble electromagnetic radiations.
2. Travel at speed of light i.e. 3*10 8 m/s.
3. They can not be focused.
4. They obey laws of polarization and interference.
5. They satisfy the “inverse square law” i.e. Intensity
of x ray beam at a given point varies inversly as a
square of the distance of that point from the source
of radiation(focus spot).
When high speed electrons lose energy in the target of
the x-ray tube
2 processes of
General radiation ( Bremsstrahlung)
• High speed electrons with nucleus of the tungsten atom
• High sped electrons with the electrons in the shell of tungsten atoms
THERE ARE MANY
PRODUCED IN ONE ATOM
IS ALSO POLYENERGETIC !
Is the conversion of alternating current (AC) to
direct current direct current ( DC) during the first
phase of AC cycle cathode is negatively charged
and anode is positevely charged electrons hit
against the anode and x rays are produced but
when current changes in direction during second
phase catode becomes positively charged
therefore electrons present at anode (because the
thermionic emission secondary to heat produced )
travel backwards & hit against the fillament ,
thereby causing burnout of the filament such a
phenomenon takes place in general x ray
In dental x ray machine however the amount
of heat produced at the anode does not give
rise to excess of electrons as result when
current changes its direction there are no
electrons at the anode to travel back to cathode
and hence dental x ray tube is called as self
ORAL RADIOLOGY . Principles and
interpretation white and pharroh 5th edition
Fundamental of physics of radiology –meridith ,
Textbook of dental and maxillofacial radiology :
freny r karjodkar
O’ briene RC the nature and generation of x ray
Internet : www.pubmed .org