Health Physics
1a: Sources of Radiation
Introduction
• Scientists have studied radiation for over 100
years and we know a great deal about it.
• Radiation is part of nature. All living creatures,
from the beginning of time, have been, and are still
being, exposed to radiation.
We Live (And Have Always Lived) in a
“Sea of Radiation”
Types of Radiation
Absorbed Dose
Depends on:
• Whether material is inside or outside body
• How long material remains in the body
• How much radioactive material there is
• The type of radiation it emits
• What its half-life is
Natural and Man-Made
Radiation Sources
Natural Background Radiation
• Cosmic Radiation
• Terrestrial Radiation
• Internal Radiation
Cosmic Radiation
• The earth, and all living things on it, are
constantly being bombarded by radiation
from outer space (~ 80% protons and 10%
alpha particles).
• 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 differences
in elevation and to the effects of the earth’s
magnetic field.
Terrestrial Radiation
(Uranium, Actinium, Thorium decay series)
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Radioactive material is found throughout
nature in soil, water, and vegetation.
Important radioactive elements include
uranium and thorium and their radioactive
decay products which have been present
since the earth was formed billions of years
ago.
Some radioactive material is ingested with
food and water. Radon gas, a radioactive
decay product of uranium is inhaled.
The amount of terrestrial radiation varies in
different parts of the world due to different
concentrations of uranium and thorium in soil.
Internal Radiation
•
People are exposed to radiation from radioactive
material inside their bodies. Besides radon, the most
important internal radioactive element is naturally
occurring K-40, but uranium and thorium are also
present as well as H-3 and C-14.
•
The amount of radiation from potassium-40 does not
vary much from one person to another. However,
exposure from radon varies significantly from place to
place depending on the amount of uranium in the soil.
•
On average, in the United States radon contributes
55% or all radiation exposure from natural and manmade sources. Another 11% comes from the other
radioactive materials inside the body.
Enhanced Natural Sources
• Air travel (cosmic rad. is increased)
• Accumulation of rad. material
(uranium)
• Consumer products (radium dials,
smoke detectors)
Locations of Operating Nuclear
Reactors
Transportation Safey
• A 120-ton locomotive,
speeding at 80 miles an hour,
crashed broadside into a
container on a flatbed.
• This photo was taken
immediately after impact.
• The impact demolished the
train, but hardly dented the
container.
Man-Made Radiation
Radioactive material is used in:
• Medicine - diagnostic (X-ray, CAT)
• Medicine - therapeutic (Co-60, Linac)
• Medical research (radio-pharmaceuticals, accel.)
• Industry - (X-ray density gauges, well logging)
Radiation in Medicine
• Radiation used in
medicine is the largest
source of man-made
radiation.
• Most exposure is from
diagnostic x-rays.
Man-Made Radiation Sources
• Exposure of selected groups of the
public:
– diagnostic radiology (X-rays)
– nuclear medicine
(radiopharmaceuticals)
– radiotherapy (Co-60, Linacs)
Man-Made Radiation Sources
• The Canadian Nuclear Safety Commission
regulates exposure from man-made radiation
sources. Different regulations apply to two distinct
groups:
–Members of the public
–Nuclear Energy Workers (NEWs)
Average Annual Effective Dose in US
population (1982)
mSv
Natural Background
Radon
2.0
other
1.0
Occupational
0.009
Medical
diagnostic X-rays 0.39
nuclear medicine 0.14
__________________________________
Total (rounded)
3.6 mSv / year
From: Mettler et al., Ionizing Radiation
Total: 3.6 mSv/y
Natural Background
and Radiation Risk
• Use background radiation to quantify
risk to a lay person.
• Background Equivalent Radiation
Time (BERT).
• Regulatory limits based on natural
radiation (1mSv/year for members of
the public).
Radiation Risk
Consent Form:
• 5mSv may increase fatal cancer risk by 2 in
10’000 in a lifetime.
• Similar risks are associated with:
- smoking 2 packs of cigarettes in a
lifetime
- driving 2000 miles by car
- living 100 days in New York
N.B.: natural incidence of fatal cancer is about 1 in 3.
Radiation Use at MNH/I
• Laboratories: 0.1 to 1 mCi
H-3, C-14, P-32, S-35, Cr-51, I-125, Ge-68
• Gamma Cell: 600 Ci of Cs-137
• PET scan: 10 to 100 mCi
C-11, O-15, F-18 (FDG)
• Cyclotron: 100 mCi to 1 Ci
C-11, O-15, F-18, neutrons
Examples on Nonionizing
Radiation Sources
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Visible light
Microwaves
Radios
Video Display Terminals
Power lines
Radiofrequency
Lasers
Biological Effects
• Lasers (e.g. in patient alignment equipment)
– Permanent eye injuries
– Cataracts and temporary blinding
– Skin damage