3. RADIATION QUANTITIES AND UNITS
• Radiation :
Radiation is energy that comes from a source
and travels through space at the speed of light. This
energy has an electric field and a magnetic field
associated with it, and has wave-like properties.
History of RADIATION :
December 1895, Wilhelm Roentgen accidentally
discovered the basic properties of x‐rays when he
captured an x‐ray image of his wife's hand. This led to
further discoveries in the properties of ionizing
radiation and the possibility of using radiation in
medicine.
4. Cont…
History of RADIATION
• Pierre Curie, Marie Curie discovered
polonium and radium in 1898. In 1903 they
won the Nobel Prize for Physics for
discovering radioactivity.
• 1942- Enrico Fermi started the first sustained
nuclear chain reaction in a laboratory beneath
the university of Chicago football stadium.
• 1945- Nuclear bombs dropped on Japan.
5. Radiation Sources
Sources of radiation can be divided into two
categories :
• Natural background radiation
• Man-made radiation
7. Cosmic Radiation
• The earth, and all living things on it,are constantly
bombarded by radiation from outer space.
• Charged particles from the sun and stars interact
with the earth’s atmosphere and magnetic field
to produce a shower of radiation.
• The amount of cosmic radiation varies in different
parts of the world due to difference in elevation
and to effects of the earth’s magnetic field.
• 35 mrad/ yr normal attitude
• Jet pilots- 300 mrad/ yr
8. Atmospheric Radiation
TERRESTRIAL
• Radioactive material is also found throughout
nature in soil , water and vegetation.
• Important radioactive elements include
uranium,thorium, radium and isotopes of
potassium(k40)
9. • Some radioactive material is ingested with
food and water
• The amount of terrestrial radiation aprox.50
mrad/yr
• ATMOSPHERIC : gases like Radon and Thorum
2 mrad/yr
10. Internal Radiation
• People are exposed to radiation from
radioactive material inside their bodies.
Besides radon, the most important internal
radioactive element is naturally occuring
potassium- 40. Others – uranium,thorium ,
strontium and carbon.
• 25 mrad/ yr
• May go upto 70 or 80
• Total natural radiation -0.1 rad/yr
11. MAN-MADE RADIATION SOURCES
Examples of man-made sources of radiation to
members of the public :
• Lantern mantles
• Medical diagnosis
• Building materials
• Nuclear power plants
12. • Coal power plants
• Tobacco
• Phosphate fertilizers
• T V sets
• Radium watches
13. NUCLEAR FALL OUT
• Fallout is the residual radioactive material
propelled into the upper atmosphere
following a nuclear blast
• Carbon C14,Iodine I131,Cescium Cs137 and
Strontium Sc 90
• The Chernobyl disaster was a nuclear reactor
accident in the Chernobyl Nuclear Power Plant
in the Soviet Union on 26 April 1986
14. Radiation
Ionizing Radiation
• Higher energy electromagnetic waves ( gamma )
or heavy particles ( beta and alpha).
• High enough energy to pull electron from orbit.
Non-ionizing Radiation
• Lower energy electromagnetic waves.
• Not enough energy to pull electron from
orbit,but can excite the electron.
15.
16. Non-Ionizing Radiation
Defintion:
They are electromagnetic waves incapable of
producing ions while passing through
matter,due to their lower energy.
Sources
• Ultraviolet light
• Visible light
• Infrared radiation
17. • Microwaves
• Radio and tv
• Power transmission
Nonionizing Examples
• Ultraviolet- Black light – induce fluorescence
in some materials
18. • Vision-very small portion that aniamls use to
process visual information
• Heat- infrared- a little beyond the red
spectrum
• Radio waves-beyond infrared
19. • Microwaves
• Electric power transmission- 60 cycles per
second with a wave length of 1 to 2 million
meters
20.
21. Ionizing Radiation
• Definition :
It is a type of radiation that is able to disrupt
atoms and molecules on which they pass
through ,giving rise to ions and free radicals.
Sources:
x-rays, radioactive material produce alpha,
beta, and gamma radiation, cosmic rays from
the sun and space.
22. Radioactive Material
• Either natural or created in nuclear reactor or
accelerator
• Radioactive material is unstable and emits
energy in order to return to a more stable (
particles or gamma rays )
• Half- life time for radioactive material to decay
by one-half
23. Types of Ionizing Radiation
ALPHA PARTICLES
• Two neutrons and two protons
• Emitted from nucleus of radioactive atoms
• Transfer energy in very short distance (10cm in
air)
• Shielded by paper or layer of skin
• Primary hazards from internal exposure
• Alpha emitted can accumulate in tissue (
bone,kidney,liver,lung,spleen ) causing local
damage .
24. BETA PARTICLES
• Small electrically charged particles similar to
electron
• Charge of -1
• Ejected from nuclei of radioactive atoms
• Emitted with various kinetic energies
25. • Shielded by wood ,body penetration 0.2 to 1.3
cm depending on energy
• Can cause skin burns or be an internal hazard
of ingested
26. GAMMA RAYS
• Electromagnetic photons or radiation
• Emitted from nucleus of radioactive atoms-
spontaneous emission
• Emitted with kinetic energy related to
radioactive source
• Highly penetrating –extensive shielding
required
• Serious external radiation hazard
27. X-RAYS
• Overlap with gamma rays
• Electromagnetic photons or radiation
• Produced when electrons strike a target
material inside and x-ray tube
• Emitted with various energies and
wavelengths
29. Properties of nuclear radiations
• High ionizing power: Alpha radiation
• Moderate ionizing power: Beta radiation
• Low ionizing power: gamma and xrays
• High penetrating power: gamma and xrays
• Moderate penetrating power: beta rays
• Low penetrating power: alpha rays
30. RADIATION UNITS
• Exposure: Roentgen (R) =amount of X or
gamma radiation that produces ionization
resulting in 1 electrostatic unit of charge in 1
cm3 of dry air
• Absorbed dose: rad ( Reontgen absorbed
dose) =absorption of 100 ergs of energy from
any radiation in 1 gram of any material ;n1
Gray(Gy)=100 rads =1 joule/kg; Exposure to 1
Reontgen approximates 0.9 rad in air
31. • SI Unit for radiation exposure
Coulombs/kilogram (c/kg)
• SI Unit for absorbed dose
Gray (Gy)
1 Gy =100 Rad
• SI Unit for activity
Becquerel (Bq)= 1 disintegration/ second
