Basic Radiation Protection
Principles
Presented by Mohamed Al-Mughrabi
Training Course on Protection Against
Nuclear Terrorism: Security of Radioactive
Sources
Riyadh, Saudi Arabia—April 2008
IAEA
International Atomic Energy Agency
Basic Radiation Protection Principles
(for non-specialists)
Objectives
After this session, participants should be able
to:
Explain what radioactivity and radiation are
1. Describe how radioactivity and radiation are
measured
2. Explain how radiation can cause harm to
humans
3. Explain how radiation may be protected
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against
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Basic Radiation Protection Principles
What is radiation?
Some atoms have unstable nuclei
• due to the ratio of neutrons and protons in their
nuclei
The instability means that the nucleus of
an atom breaks apart (“decays”) into
• fragments of the nucleus, and
• energy
• The process of a nucleus decaying is
“radioactivity”
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Basic Radiation Protection Principles
What is radiation?
The fragments may be
New (smaller and different) atoms
• that are radioactive themselves
• “daughter nuclei”
• or
• New (smaller and different) atoms
• stable atoms that do not decay any further
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Basic Radiation Protection Principles
What is radiation?
The energy is called “radiation”
• It is given off in “packets” of various types
• confusingly, some of the radiation is
• “pure energy” and some
• is energy and mass together
The phenomenon of atoms breaking up due
to instability is called “radioactive decay ”
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Basic Radiation Protection Principles
What is radiation?
• Radiation emitted by each radioactive
element has its own characteristic energy
• This often means the type of radioactive
material can be easily identified
• by its characteristic energy
• if the correct instrument is used
• In most (but not all cases) it is fairly easy to
establish what the hazards are
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Basic Radiation Protection Principles
Radioactive decay and half-lives
• Radioactive elements decay at own
characteristic rate
• The rate is described by its “half-life”:•
•
If we start with 64 million atoms:
•
•
Time for the number of atoms present to reduce by half
After one half life there will be 32 million atoms left
After a second half life
• IAEA
there will be 16 million atoms left, and so on
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Basic Radiation Protection Principles
Radioactive decay and half-lives
Some radioactive elements have a very
long half-life:
• Plutonium-239 has a half life of 24 000 years
• Radium has a half-life of 1600 years
Other radioactive elements have a short
half life
• Caesium-137 has a half-life of 30 years
• Polonium-210 has a half-life of 138 days
• Iodine-131 has a half-life of 8 days
IAEA10 half-lives 0.01% of the original
After
quantity remains
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Basic Radiation Protection Principles
What is radiation?
A substance that is radioactive is often called
“radioactivity”
The energy it gives off when it decays is called
“radiation”
Radioactivity is a substance
• (powder, gas or liquid)
Radiation is essentially energy;
• like light it “shines”
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Basic Radiation Protection Principles
Types of radioactivity and sources
• Naturally Occurring Radioactive Material (NORM)
• Uranium, Thorium, Potassium (in living things)
• Artificially made radioactive material
• Cobalt, Caesium, Plutonium, Polonium
• Open sources are radioactive powders, gases, liquids
• used in experiments like any chemical
• Sealed sources are steel capsules that permanently
contain the radioactivity
• The radioactivity is always contained; the radiation shines
• (unless damaged by impact, explosion, melting or human intervention)
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Basic Radiation Protection Principles
What is radiation?
Like light, radiation cannot be stored in a
container
BUT
• The radioactivity that emits it can be
stored in a container
If container is broken, the substance leaks
out
• It contaminates the environment / person
• It is often called “contamination”
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• Remember,
it is still emitting radiation!!
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Basic Radiation Protection Principles
What is radiation?
Like light, radiation can be blocked out
Light: may only need a piece of paper or plastic tape
• With some types of radiation paper may
work too.
BUT
• other types of radiation can penetrate
•
even metal or concrete (or people)
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Basic Radiation Protection Principles
What is radiation?
When radiation penetrates materials it loses
some of its energy into the material
• If the material is dense enough, or thick
enough, all the energy may be lost to the
material and the radiation is totally blocked
• Usually, some will get through, but there will
be less of it, and it will be weaker
• The material has acted as a “shield” to the
radiation
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Basic Radiation Protection Principles
What is radiation?
As energy is lost to the material that the
radiation passes through it knocks electrons
off atoms of the material
• Atoms that have lost an electron are called
“ions”
• they too are “energetic” and react further
• This phenomenon is called ionisation
• The
radiation is said to be “ionising
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radiation”
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Basic Radiation Protection Principles
What is radiation?
Ions are very reactive atoms
• They react chemically with other atoms
around them,
• especially water
• They may ionise things too
• The ionic and chemical reactions are
common in water
• People are 70% water
• Radiation can cause chemical changes in people
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Basic Radiation Protection Principles
What is radiation?
As animals are mostly water, radiation causes
a lot of ionisation and chemical change in
them – damage
• The damage can be minor
– the body may repair it, or
• The damage may be severe
– and kill cells or tissues, or
• The damage may be moderate
– and change DNA
• Abnormal changes in DNA sometimes cause
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cancer
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Radiation damage to DNA: and double
strands
Damage to
a single
strand
DNA is the
genetic
material
within cells
Damage to
a double
strand
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DNA Double
Helix
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Basic Radiation Protection Principles
Harm caused by radiation
DNA damage
– delayed: potential effect of cancer
• (known as “stochastic effects”)
Cell or tissue damage
– early: burns or damage or death of
tissue
• (known as “deterministic effects”)
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Basic Radiation Protection Principles
External Radiation Hazards
Three main types of radiation
• Alpha – lot of energy and lot of mass
• Lot of damage per unit length of path,
• but energy used up very quickly – so very low range
• (about 3 cm in air & ~ 0.001mm in water/tissue)
• Beta
• (quite penetrating – range about 4 metres in air)
• Gamma
• (very penetrating – range tens of metres)
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Basic Radiation Protection Principles
External Radiation Hazards
Three main types of radiation not equally easy
to detect:
Alpha – lot of energy and lot of mass
• Very low range means they are difficult to detect
• Need to get very close (less than 1 cm)
• But easier in a laboratory
• Beta ( range about 4 metres in air)
• Easy to detect within a metre
• Gamma (range tens of metres)
•
Very
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Major Pathways from Release
Inhalation (γ,α,β)
Cloud
Shine (γ)
Deposition
Skin (β)
Release
Inhalation (γ,α,β)
from Resuspended Material
Ground
Ground
Shine (γ)
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Basic Radiation Protection Principles
Deterministic effects – examples
Occur early after irradiation
Cataract, burns, erythema, death
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Radiation Sickness
Very high (acute) doses
of radiation kill cells and
tissues:
If the body cannot repair
the damage, death
follows due to
Bone marrow damage:
– blood effects;
Damage to gut, kidneys
etc;
Highest doses, damage
brain
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Death due to deterministic effects
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Basic Radiation Protection Principles
Protection from radiation
External hazards (“Shine”)
• Alphas cannot penetrate the outer layers of skin
• So alpha radioactivity is not an external hazard
Control of external hazards is by three simple
principles:
• Time – minimise the time near to a source of
radiation
• Distance – maximise the distance from a
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source
• Shielding – use anything which will block
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Basic Radiation Protection Principles
Protection from radiation
Internal hazards
Alphas very dangerous inside the body
• densely ionising
• Beta and gamma less so
• (much energy escapes the body)
• but still a hazard
Prevent:
•
•
•
•
Ingestion
Inhalation
Absorption
Injection
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- (no eating/drinking)
- (keep air clean for breathing)
- minimise or prevent contact / touching
- prevent wounds
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Major Pathways from Release
Inhalation (γ,α,β)
Cloud
Shine (γ)
Deposition
Skin (β)
Release
Inhalation (γ,α,β)
from Resuspended Material
Ground
Ground
Shine (γ)
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Basic Radiation Protection Principles
Is there any good news?
• Radiation is easily detected with the correct instruments
• Modern instruments are highly sensitive
• They all rely on detecting ionisations to:
– Generate an electronic pulse
– Or a flash of light
– Counted electronically
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Basic Radiation Protection Principles
Is there any good news?
• Radiation is easy to measure accurately
• Risks due to radiation are well understood
• Better than probably any other hazard
• Straightforward to protect from excess risk
• Doses can be kept below safe limits and
• As low as reasonably achievable (ALARA)
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Basic Radiation Protection Principles
What have we learned so far?
• Radioactivity is a decay process
• The same term is used (in English) for a
substance
• Radiation is mainly energy
• It does harm by ionising things it passes
through
• It can cause early “deterministic” effects
• And /or delayed “stochastic” effects (cancer)
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• But
because radiation is well understood
and easy to measure, it is possible to
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Basic Radiation Protection Principles
What can go wrong?
• Lost sources often find their way into the metals recycling industry
• Sources stolen for the scrap value of the container/metal device
• Some evidence that terrorists want sources to make weapons
• Value of a radioactive weapon depends on corruption of radiation
protection principles to maximise harm:
• Radiation harm
• Anxiety, confusion, stress
• Disruption
We will look at some of these effects later
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Summary
• Radiation is energy like light – it shines
from…
• Radioactivity – that is a substance
• If radioactivity leaks from its container it
contaminates surfaces (including people)
• Radiation can harm people so we need to
take precautions
• Fortunately this is easy to do with the right
equipment
and training
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