1. EM RADIATION &
PHYSICS OF XRAYS
DR ZOHEIR HUSSEIN

2. ATOMIC THEORY
 Matter is comprised of very small particles
known as atoms.
 Atoms are can be further subdivided into 3
basic subatomic particles:
- protons (p+)
- neutrons (nº)
- electrons (e¯)

3. Historical Overview
 The Greeks theorized that matter has four basic
components: air, water, earth and fire.
 Named the smallest division of these components the atom.
 Theory accepted until early 1800s, when English
schoolteacher John Dalton (1766-1844) published his
work on atomic theory:
 Elements differentiated from one another based on the
characteristic of mass
 Elements composed of atoms which behaved in an identical
fashion during a chemical reaction.

4.  1800s: Russian scientist, Dmitri Mandeleev (1834-
1907), developed the first periodic table of the elements:
 elements are arranged in order of ascending atomic mass
 1911: English physicist Ernest Rutherford (1871-1937)
developed a model for the atom which contained a
central, small, dense nucleus, which possessed a positive
charge and was surrounded by a negative charge.
 1913: Niels Bohr (1885-1962), a Denish physicist,
expanded on Rutherford’s work and proposed a model
for the atom which is considered the most representative
of the structure of matter.
 Bohr’s atom is likened to a miniatures solar system where
electrons orbit around a central nucleus just as the planets
revolve around the sun.

5. Basic Atomic Particles
 The atom - small, dense centre the nucleus,
which is surrounded by –vely charged electrons
that orbit it at various levels.
 Nucleus – protons (+ve) and neutrons (neutral)
 Protons + neutrons = Atomic mass
 Electron has a relatively insignificant mass,
1/1,828 that of a proton ( 9.109 x 10-31 kg)
 Proton – 1.673 x 10-27 kg
 Neutron – 1.675 x 10-27 kg

6.  When the number of
positively charged protons
equals the number of
negatively charged
electrons, the atom is
neutral or stable.
 Because of its electrical
nature, the atom is dynamic
and ever moving and in a
constant, vibrating motion
because of the strong
positive nuclear force field
which is surrounded by the
negatively charged spinning
and orbiting electron.

7. Atomic Number
 Each elements has its own specific number of nuclear
protons.
 This is the key characteristic which distinguishes one
element from another.
 The number of nuclear protons in an atom is known as
the atomic number or z number.
 The simplest element, hydrogen, possesses only one proton
and therefore has atomic number of 1.
 Helium comes next on periodic table and has two protons,
giving it an atomic number of 2.
 Lead has an atomic number of 82, indicating that within the
nucleus of an atom of lead there are 82 protons.

8.  In a neutral atom the number of protons is equal to the number
of electrons.
-In a stable, neutral atom of hydrogen there is one proton and
one electron.
-In a stable atom of lead there are 82 protons and 82 electrons.
 If an atom gains or loses neutrons, the result is an atom called
an isotope.
-Isotopes are atoms which have the same number of protons in
the nucleus but differ in the number of neutrons.
-Deuterium is an isotope of hydrogen, contains the same
number of protons as hydrogen but also contains one neutron.
 If an atom gains or loses an electron, it is called an ion and the
atom is said to be ionized.

9.  Ionization is the process of adding or
removing an electron from an atom.
ie when an electron is removed from an atom,
the atom becomes a positive ion; that is the
atom possesses an extra positive charge.
When an electron is added to an atom, the
atom becomes negative ion, ie it possesses an
extra negative charge

10. EM Radiation
 In terms of modern quantum theory:
EM wave is the flow of photons (also called
light quanta) through space.
 Photons are packets of energy that aways
move with the universal speed of light
(300,000 Km/sec)

11.  Electromagnetic radiation (EM) spans a
continuum of wide ranges of magnitudes of
energy.
 This continuum is termed the electromagnetic
spectrum.
 The electromagnetic spectrum details all of the
various forms of EM radiation.
 One of the common properties of all forms of
EM radiation is velocity.

12. Electromagnetic spectrum
 High energy – Gamma
- X- ray
- Ultraviolet
- VISIBLE LIGHT
- Infrared
- Microwave
- Radar
 Low energy - Radio

14.  Radiation along the EM spectrum will vary
according to the associated frequency and
wavelength.
 Low frequency-long wavelengths are at the
bottom of the spectrum with radio waves and
microwaves.
 Visible light is in the centre of the spectrum
and at the top of the spectrum are gamma and
x-rays having high frequency and short
wavelengths.

16. IONIZING RADIATION
 IR arises from both natural and manmade
sources grouped as Particulate and EM
(Photon) radiation
 Particulate- high energy electrons, protons and
neutrons.
Produce ionization by direct atomic collisions
 Photon radiation- X-rays Gamma rays
Produce ionization by other types of
interactions (photoelectric absorption,
compton scattering)

17. S O U R C E S O F R A D IA T IO N
NATURAL A R T IF IC IA L
EXTERNAL IN T E R N A L IN D U S T R IA L M E D IC A L
C O S M IC T E R R E S T IA L IN G E S T E D IN H A L E D NUCLEAR W EAPONS D IA G N O S T IC T H E R A P E U T IC
O UTER SPACE E N V IR O M E N T A L K&C RADON REACTO RS

18. NATURAL SOURCES OF RADIATION

19. Ionizing radiations in diagnostic
imaging
 X-RAYS:
 Conventional Radiography
 Fluoroscopy
 Mammography
 CT-scan
 GAMMA RAYS:
 Radioisotope scanning

20. Properties of Ionization radiations
 They have a very short wavelength and so can
penetrate materials
 They can cause certain substances to fluoresce
 They form an image on a radiographic film
 They produce biological effects which may be
useful as in radiation therapy or harmful as to
cause disease

21. RADIO-SENSITIVITY (RS) OF VARIOUS
HUMAN ORGANS
High RS Medium RS Low RS
Bone Marrow Skin Muscle
Spleen Mesoderm Bones
Lymphatic Organs (liver, Nervous system
Nodes heart, lungs)
Gonads
Eye Lens
Lymphocytes

22. Radio-sensitivity
 RS - probability of a cell, tissue or organ of
suffering an effect per unit of dose.
 Bergonie and Tribondeau (1906): “RS
LAWS”: RS will be greater if the cell:
• Is highly mitotic.
• Is undifferentiated.
• Has a high carcinogenic future.

23. Biologic effects of ionizing radiations
 Photons of ionizing radiation absorbed by atoms of water
molecules of the cell- 1˚ ionization.
 The ejected electron has sufficient energy to cause ionization
of other atoms in the material- 2˚ ionization.
 The free formed combine with others to form a new chemicals
in the cell- chemical change.
 This chemical change causes abnormal behavior of the cell-
Biological change.
 The effects of these changes are stochastic and non-stochastic
effects.

24. Stochastic effect
 Is defined as an effect in which the probability
of occurrence increases with increasing
absorbed dose, but severity of effect does not
depend on the magnitude of the absorbed dose.
 It is an all-or-none phenomenon, and is
assumed to have no dose threshold so higher
the dose higher the risk.

25. 3 important consequences of stochastic effect are:
 Radiation induced carcinogenesis of which
leukemia is the commonest neoplasia.
 Congenital malformations from effect during
organogenesis.
 Mutations due to altered biological code on
chromosomes in germ cells (sperm & ova)

26. Non stochastic effect
 Is defined as a somatic effect that increases in
severity with increasing absorbed dose. So
there is a threshold below which the effect will
not occur or will be stochastic.
 These are usually degenerative effects severe
enough to be clinically significant.
 They usually occur in industrial disasters.

27.  1Sv- Temporary depression of blood count but the
victim is likely to recover or may develop stochastic
effect.

 5Sv- Death can occur within weeks due to bone marrow
failure, unless radical medical intervention is effected.
 10Sv- Death occurs within days due to damage of the
GIT lining leading to infections, septicemia or
hemorrhage.
 20Sv- Death within hours due to severe damages to CNS
from the cellular debris and not the radiation directly.

28. METHODS OF PROTECTION
 Who should be protected: Parameters available to
Patients reduce radiation exposure
Staff  Time
General public  Reduce time of exposure
 Protected against:  Distance
Primary / useful radiations  By inverse square law
Stray radiations I.e.  Barriers
 Scatter  Filters
 Leakage  Lead shields
 Concrete walls

29. PROTECTION TECHNIQUES
 Use Posters e.g. Radiation
symbol
 Inverse square law (D α 1/S2)
 Date of LNMP
 Lead sheets/iron sheets
 Quality assurance
 Renewable license

32. PATIENTS
 Use of Aluminum filters close to the tube
 Tube shielding
 Reduce field size with collimation
 Use fast film/screen combination
 Reduce number of repeats
 Use highest possible kVp and low mAs
 Use pulsed fluoroscopy rather than continuous
 Use lowest possible time of exposure
 Use adequate protective gears

33. STAFF
 Only those required in the room should be present
 All should stand behind the barrier during exposure
 Must wear adequate protective gear
 Must be as far as possible from the primary beam
 Use immobilising devices for restless patients

34. GENERAL PUBLIC
 The radiology unit must be reinforced with concrete
walls and lead shielded doors.
 The direction of primary beam should not be directed to
the clinics or waiting areas.
 Those who are not supposed to be in Radiography suit
should be kept away.
 Should use appropriate protective gear when required.

35. Conclusion
There are no ionizing radiations
which are completely safe
It is of utmost importance to avoid unnecessary
ionizing radiations and the radiation exposure
should be kept as low as reasonably
achievable (ALARA)