Wilhelm Conrad Röentgen was a German physicist who discovered x-rays in 1895. He was awarded the first Nobel Prize in Physics in 1901 for his discovery. Röentgen discovered x-rays accidentally while experimenting with cathode ray tubes. He noticed a fluorescent glow coming from a nearby screen and realized some new type of radiation was causing this. When he placed his wife's hand on photographic plates and exposed them to this radiation, the outline of bones in her hand appeared on the developed plate. This led him to name this new type of radiation "x-rays".

2. Wilhelm Conrad Röentgen
• Professor of Experimental
Physics
– Würzburg University
• Discovered x-rays
– 8 November, 1895
• Awarded first Nobel
Prize for Physics
– 1901

3. History of x-ray:
• Roentgen placed his wife’s
hands on photographic
plate and exposed it to
unknown radiation for 15
minutes.
• When he developed the
photographic plate, the
outline of bones of her
hand could be seen.
• He named it x-ray.

4. Nature of the atom:
• Simple substances are called elements. There are 105
elements.
• The atom is the smallest particle of an element that has
the characteristic properties of that element.
• It consists of nucleus surrounded by orbital electrons.
• The nucleus is composed of protons and neutrons and
they are called nucleons.

5. • XAtomic number (Z): is the number of
protons inside the nucleus that equal
the no. of electrons . It determine the
chemical properties of atom & identify
the identity of element.
• XMass number (A): the total number of
protons & neutrons (nucleons).
A
• Nuclide is defined as zX

6. • Electrostatic force is a
force between positively
charges nucleus and
negatively charged
electrons (attracting
force) balances the
centrifugal force of
rapidly moving electrons .
• That keeps electrons
maintained in their shells.

7. • Electron Binding
energy (Ionization
energy):
• It is the energy
required to remove
electron from a given
shell.
• It should exceeds the
eletrostatic force
binding that electron to
nucleus.

8. Atom (cont.)
• The inner shells have more binding energy
more than outer shells.
• E.g. K-shell > L-shell> M-shell ..etc.

9. Ionization:
• Atom is ordinary neutral as the
number of electrons equal the number
of protons.
• If atom loses an electron, it becomes a
positive ion and free electron is a
negative ion.
• This process of forming an ion pair is
termed Ionization.

10. Ionization (cont.)
• XIonization of inner shell electrons
(K, L) require high energy to be
ejected from their orbit (X-ray,
Gamma rays or high energy particles)
.
• Ionization of electrons on outer shells
require low energy particles (ultraviolet)

12. Nature of radiation:
• X1- Corpuscular or particulate
radiation:
• A minute particles which have mass &
charge traveling at straight line with high
speeds.
• A- Alpha Particles: composed of Helium
nuclei (2P+2N) without orbital electrons.
• Because of their double charge & heavy
mass they loss their energy very quickly
and have shallow tissue penetration .

13. Nature of radiation (cont.)
• B- β- Particles:
• They are emitted from nuclei of radioactive
atoms & possess 1 unit of negative charge.
• They are more penetrating than α-particles.
• C- Cathode Rays (electrons):
• Streams of electrons passing from the hot
filament of cathode to anode target in x-ray
tube.

14. Nature of radiation (cont.)
• The capacity of particulate radiation to
ionize atoms depends on its ;
• Mass, velocity and charge.
• The rate of loss of energy from a
particle as it moves along its track
through matter (tissue) is called Linear
Energy Transfer (LET).
• The slower heavy particles have higher
LET.

15. Nature of radiation (cont.)
• 2- Electromagnetic radiation:
• It is a propagation of energy through space
accompanied by electric and magnetic force field
where they are perpendicular to each other. e.g. Xray & Gamma rays.
• Electromagnetic radiations are arranged according
to their energies in what is termed electromagnetic
spectrum.

16. Nature of radiation (cont.)
• Electromagnetic spectrum (EMS):
• Energies in EMS are grouped according their
wavelengths or energy of their photons .
• They ranges from radio-waves to gamma & xrays.

17. Nature of radiation (cont.)
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EM radiation regard as both a particle & wave.
Particle concept:
Discrete bundle of energy → Photons
( Quanta).
Photons have no mass or weight travel in straight line & carrying EM
energy.
Wave concept:
EM radiation → Waves characterized by;
1- Velocity →speed of wave (speed of light 3×108 m/s).
2- Wavelength (λ) → distance between the crest of one wave & the
crest of the next.
3- frequency (F): refers to the number of wavelengths that pass a
given point in a certain amount of time.
C= λ√ (lambda × nu)
C= velocity of light, λ= wavelength in meters, √= frequency in hertz
(cycle per second).

18. Waves
Short Wavelength
Long wavelength
•
•
•
•
wavelength
All light waves travel at the same speed, c = 300,000 km/s
Wavelength is the distance between two crests of the wave
Frequency is the number of crests that pass by you in a
second
The longer the wavelength, the lower the frequency, the lower
the energy of the photon

19. What are x-rays?
• XA weightless bundles of energy
(photons) without an electrical charge that
travel in waves with a specific frequency at
the speed of light. X-ray photons interact
with the materials they penetrate and
cause ionization.

20. Properties of x-ray
X1- x-ray are invisible and weightless.
2- They travel in straight line.
3- They travel at the speed of light.
4- They have a wide range of wavelengths.
5- They can not be focused to a point; over
distance the beam diverges like beam of
light.

21. Properties of x-ray (cont.)
6- due to their short wavelengths , they penetrate
materials that absorb or reflect visible light.
7- They are absorbed by matter; that depends on
atomic structure of matter and wave-length of xray.
8- They cause certain substances to fluoresce ; to
emit radiation of long wavelength (visible or
ultraviolet rays).
9- they produce biologic changes in living cells.
10- they can ionize gases and materials they
penetrate.

22. Interaction of x-ray with a matter:
• When x-ray photons
arrive at the patient , one
of several events may
occur;
• 1- x-ray can pass through
the patient without any
interaction.
• 2- x-ray photons can be
completely absorbed by
the patient.
• 3- x-ray photons can be
scatered.

23. Interaction of x-ray with a matter(cont.):
• At the atomic level 4 interactions could be
occur when x-ray photons interact with
matter;
• 1- No interaction.
• 2- Absorption or photoelectric effect.
• 3- Compton scatter.
• 4- Coherent scatter.

24. 1- No interaction:
• The x-ray photon
passes through the
atom unchanged and
leaves the atom
unchanged.
• It is responsible for
producing densities on
film and make dental
radiography possible.

25. 2- Absorption & Photoelectric effect:
• Absorption:
• X-ray photon may be completely
absorbed by tissue.
• At atomic level absorption occurs
as a result of the photoelectric
effect.
• An x-ray photon collides with a
tightly bound, inner shell electron
and give up all of its energy to
eject the electron from its orbit.
• The ejected electron is termed a
photoelectron and has a negative
charge and absorbed by another
atom.
• The photoelectric effect accounts
for 30% of dental x-ray.

26. 3- compton scatter
• X-ray photon may be deflected
from its path as it termed
scatter.
• In compton scatter , x-ray
photon collides with loosely
bound, outer shell electron and
gives up part of its energy to
eject it .
• The ejected electron is termed a
compton or recoil electron with
negative charge.
• Compton scatter accounts for
62% of the scatter in diagnostic
radiology.

27. 4- coherent scatter:
• A coherent or unmodified
scatter occurs when a low
energy x-ray photon interacts
with outer shell electron.
• No change or no ionization
occurs.
• The x-ray photon is scattered in
different direction than the
incident photon.
• The x-ray photon is unmodified
and simply change its direction
without change in energy.