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We
cannot eliminate radiation from our environment. We can,
however, reduce our risks by controlling our exposure to
it.
Understanding radiation and radioactivity will help you
make informed decisions about your exposure.
What is radiation?
Radiation
is energy that travels in the form of waves or particles.
When
we hear the word ' radiation,' we generally think of nuclear
power plants, nuclear weapons, or radiation treatments
for cancer. We would also be correct to add 'microwaves,
radar, electrical power lines, cellular phones, and
sunshine' to the list. There are many different types of
radiation that have a range of energy forming an electromagnetic
spectrum. However, when you see the word 'radiation' on this
Website, we are referring to the types of radiation used
in nuclear power, nuclear weapons, and medicine. These
types of radiation have enough energy to break chemical bonds,
and are referred to as 'ionizing radiation.' |
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What
is radioactivity?
The radioactivity
is the property of some atoms to spontaneously give off energy
as particles or rays. The atoms that make up the radioactive
materials are the source of radiation. To
be able to understand radiation and radioactivity, you need
to understand the language of atomic structure: |
Atoms
are the extremely small particles of which we, and
everything around us, are made. A single element, such
as oxygen, is made up of similar atoms. Different elements,
such as oxygen, carbon, and uranium contain different
kinds of atoms. There are 92 naturally occurring elements
and scientists have made another 17, bringing the total
to 109. Atoms are the smallest unit of an element that
chemically behaves the same way the element does.
When
two chemicals react with each other, the reaction
takes place between individual atoms--at the atomic
level. The processes that cause materials be
radioactive--to emit particles and energy--also occur
at the atomic level.
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Atomic Structure
In
the early 20th century, a New Zealand scientist, Ernest Rutherford,
and a Danish scientist, Niels Bohr, developed a way of thinking about
the structure of an atom that described an atom as looking very
much like our solar system. At the center of every atom was a nucleus,
which is comparable to the sun in our solar system. Electrons moved
around the nucleus in "orbits" similar to the way
planets move around the sun. (While scientists now know that
atomic structure is more complex, the Rutherford-Bohr model is
still a useful approximation to begin understanding about atomic
structure.)
nucleus
contains small particles: protons and neutrons. |
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 neutrons
have no electrical charge. They appear to be necessary to help
bind together the positively charged protons, which naturally
repel each other.
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 protons
are positively charged particles. All atoms of an element (radioactive
and non-radioactive) have the same number of protons.
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| Particles
in the nucleus (nucleons), and the forces among them,
affect an atom's radioactive properties. |
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The
cloud of particles that orbit the nucleus are called
electrons, and are negatively charged.
Electrons
in the outer orbits affect an atom's chemical properties |
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electrons |
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What
holds the parts of an atom together?
Opposite
electrical charges of the protons and electrons do the
work of holding the nucleus and its electrons together. Electrons
closer to the nucleus are bound more tightly than the outer
electrons because of their distance from the protons in
the nucleus. The electrons in the outer orbits, or shells, are
more loosely bound and affect an atom's chemical properties.
A
delicate balance of forces among nuclear particles keeps
the nucleus stable. Any change in the number, the arrangement,
or energy of the nucleons can upset this balance and cause
the nucleus to become unstable or radioactive. (Disruption
of electrons in the inner orbits can also cause an atom
to emit radiation.)
The
amount of energy required to break up the nucleus into
its parts is called the binding energy; it is often referred
to as "cosmic
glue". This is the same amount of energy given
off when the nucleus formed. |
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| Nuclides & Isotopes |
An
atom that has an unbalanced ratio of neutrons to protons in
the nucleus seeks to become more stable. The unbalanced or
unstable atom tries to become more stable by changing the number
of neutrons and/or protons in the nucleus. This can happen
in several ways: |
- converting
neutrons to protons
- converting
protons to neutrons
- ejecting
an alpha particle (two neutrons and two protons) from the
nucleus.
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Whatever the mechanism, the atom is seeking a stable neutron
to proton ratio. In changing the number of nucleons (protons
and neutrons), the nucleus gives off energy in the form of
ionizing radiation. The radiation can be in the form of alpha
particles (2 protons and 2 neutrons), beta particles (either
positive or negative), x-rays, or gamma rays. |
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Is
the atom still the same element?
Only
sometimes. If there is a change in the number of protons, the atom
becomes a different element with different chemical properties.
If there is a change in the number of neutrons, the atom is the
same element, but becomes a different isotope of that element.
All isotopes of one element have the same number of protons but
different numbers of neutrons. All isotopes of a certain element
also have the same chemical properties but have varying radiological
properties such as half-life, or type of radiation emitted.
What if the protons and electrons of an atom are unbalanced?
Normally,
the number of electrons and protons is the same, so
the atom is balanced electrically. Sometimes electrons
are added or removed, and the atom carries a negative
or positive charge. These charged forms of an element
are called 'ions' of the element. This change affects
the way the atom reacts chemically, but does not affect
the stability of the nucleus--the atom's radioactivity.
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What
are nuclides and radionuclides?
Nuclide
is a term used to categorize different forms of atoms very
specifically. Each nuclide has a unique set of characteristics: |
- number
of protons
- number
of neutrons
- energy
state.
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If
any of these change, the atom becomes a different nuclide.
Approximately 3,700 nuclides have been identified. Most of
them are radionuclides, meaning they are unstable and undergo
radioactive decay. |
| Radiation Protection Basics |
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basic concepts apply to all types of ionizing radiation.
When we develop regulations or standards that limit how
much radiation a person can receive in a particular situation,
we consider how these concepts might affect a person's
exposure. |
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Basic Concepts of Radiation Protection
time  shielding
distance
Time  |
The
amount of radiation exposure increases and decreases
with the time people spend near the source of radiation.
In
general, we think of the exposure time as how long
a person is near radioactive material. It's easy to
understand how to minimize the time for external (direct)
exposure. Gamma and x-rays are the primary concern
for external exposure.
However,
if radioactive material gets inside your body, you
can't move away from it. You have to wait until it
decays or until your body can eliminate it. When this
happens, the biological half-life of the radionuclide
controls the time of exposure. Biological half-life
is the amount of time it takes the body to eliminate
one half of the radionuclide initially present. Alpha
and beta particles are the main concern for internal
exposure. |
Distance 
The
farther away people are from a radiation source,
the less their exposure.
How
close to a source of radiation can you be without
getting a high exposure? It depends on the energy of the
radiation and the size (or activity) of the source. Distance
is a prime concern when dealing with gamma rays,
because they can travel long distances. Alpha and beta
particles don't have enough energy to travel very far.
As
a rule, if you double the distance, you reduce the
exposure by a factor of four. Halving the distance,
increases the exposure by a factor of four. |
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Shielding 
The
greater the shielding around a radiation source, the smaller the
exposure.
Shielding
simply means having something that will absorb radiation between
you and the source of the radiation (but using another person to
absorb the radiation doesn't count as shielding). The amount of shielding
required to protect against different kinds of radiation depends
on how much energy they have.
(Alpha)
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A
thin piece of light material, such as paper, or even the
dead cells in the outer layer of human skin provides adequate
shielding because alpha particles can't penetrate it. However,
living tissue inside body, offers no protection against inhaled
or ingested alpha emitters.
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(Beta)
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Additional
covering, for example heavy clothing, is necessary to protect
against beta-emitters. Some beta particles can penetrate
and burn the skin.
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(Gamma)
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Thick,
dense shielding, such as lead, is necessary to protect against
gamma rays. The higher the energy of the gamma ray, the thicker
the lead must be. X-rays pose a similar challenge, so x-ray
technicians often give patients receiving medical or dental
X-rays a lead apron to cover other parts of their body. |
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