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
13.
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.
15.
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
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
30.
31.
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)