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1 . Differentiate among alpha and
beta particles and gamma radiation .
2 . Differentiate between fission and
fusion .
3 . Explain the process half-life as
related to radioactive decay .
4. Describe nuclear energy , its
practical application as an alternative
energy source , and its potential
problems.
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Radioactivity is the spontaneous
disintegration of atomic nuclei. The
nucleus emits α particles, ß
particles, or electromagnetic rays
during this process.
After decaying, radioactive atoms
“change” into other atoms
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• Why does the atom do this?
– the nucleus of an atom attempts to become
more stable
• In some instances, a new element is
formed and in other cases, a new form of
the original element, called an isotope,
appears.
– this process of change is often referred to as
the decay of atoms.
• The rate of Radioactive decay is
described in half-lives.
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Energy is released during radioactive decay
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Types of Nuclear
Radiation
• When an unstable
nucleus decays,
particles and energy
are given off from the
decaying nucleus.
• α and β radiation is in
the form of particles
• γ radiation is in the
form of waves-kind of
like light but higher
frequency
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Nuclear Decay
2 protons & 2 neutrons
Neutron decays into a proton
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Alpha particles consist of two protons and two
neutrons, identical to the nucleus of a helium
atom.
• A sheet of paper or a person’s surface layer of
skin will stop them.
• Alpha particles are only considered hazardous to
a person’s health if they are ingested or inhaled
and thus come into contact with sensitive cells
such as in the lungs, liver and bones.
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• Beta particles are electrons emitted from the nuclei
of many fission products.
•They can travel a few
feet in air but can usually
be stopped by clothing or
a few centimeters of
wood.
•They are considered
hazardous mainly if
ingested or inhaled, but
can cause radiation
damage to the skin if the
exposure is large enough.
•Unstable Neutron
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• Gamma rays are a form of electromagnetic
radiation (like light, radio, and television) that
come from the nucleus of a radioactive atom.
– Occurs when an unstable nucleus emits electromagnetic
radiation. The radiation has no mass, and so its emission
does not change the element.
– They penetrate matter easily and are best stopped by
water or thick layers of lead or concrete.
– Gamma radiation is hazardous to people inside and outside
of the body.
•However, gamma radiation often accompanies alpha and
beta emission, which do change the element's identity.
•Gamma rays have the lowest ionizing power, but the highest
penetrating power.
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Biological Effects of Radiation:
Ionizing radiation causes physical damage to cells and DNA.
Radiation can excite DNA and result in the destruction on the
DNA backbone.
At high doses of radiation (10,000 - 15,000 rads), death occurs
in a few hours because of neurological and cardiovascular
breakdown (Central Nervous Syndrome).
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Biological Effects of Radiation:
Medium doses, 500 - 1200 rads, causes death to occur in a
few days because of the destruction of the gastrointestinal
mucosa.
Lower doses, 250 - 500 rads, causes death to occur after
several weeks due to damage of the blood forming organs
(hematopoietic syndrome).
Radiation is used positively in a variety of ways
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Medicine
•For example, radiation and radioactive tracers
are used to diagnose and treat medical problems.
•A radioactive tracer is a radioactive isotope
that is added to a substance so that the
substance can be detected later.
•Radioactive tracers are used to locate tumors, to
study the functioning of a particular organ, or to
monitor the flow of blood.
•For example, radioactive iodine-131 is used to
diagnose thyroid problems.
•Radiation therapy used to treat cancer may
involve the use of implanted radioactive isotopes such as
gold-198 or iridium-192.
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Industry
•Manufacturers can also use radiation to
check the thickness of metal containers by
measuring the amount of radiation that
passes through.
•Small amounts of radioactive isotopes, like
magnesium-28, can be introduced in a water
source to determine the flow of underground
water or to determine if an underground water
system is leaking.
•Radioactive isotopes are even used in smoke
alarms.
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Generate electrical power
Nuclear fission is used to generate
electricity as an alternative energy
source.
Dating
Even the age of fossils or rocks can
be determined by using radioactive
isotopes.
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Fission and Fusion
Fission
Fusion
Splitting a nucleus
Combining of two nuclei.
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•Nuclear power can come from the fission of uranium, plutonium or
thorium or the fusion of hydrogen into helium.
•Today it is almost all uranium.
•The fission of an atom of uranium produces 10 million times the
energy produced by the combustion of an atom of carbon from coal.
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Issues for Fission Power Plants
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•Need for a spent fuel disposal facility
and a decommissioning plan
•Use of large amounts of water for
cooling purposes (if wet cooling towers
are used) –thermal pollution
•Biological impacts on the ocean due to
thermal discharge (if seawater cooling is
used)
•Public safety concerns
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FUSION
•A fusion reaction occurs when nuclei of light
elements, specifically hydrogen and its isotopes
(deuterium, or "heavy water," and tritium), are
forced together at extremely high temperatures and
densities until they fuse into nuclei of heavier
elements and release enormous amounts of energy.
•If fusion is to yield net energy, the fuel must be
heated in the form of plasma (a highly ionized gas) to
a very high temperature and the plasma must then be
held together for a sufficiently long time such that
the number of fusion reactions occurring releases
more energy than was required to heat the fuel.
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Half Life is the amount of time it takes
for half of the nuclei in a sample to decay
Mass
(kg)
12C
mass number
14C
13C
• Carbon occurs naturally in three
isotopes.
• All of these atoms have the same
number of protons but different
numbers of neutrons.
• The number of neutrons and protons
determines the mass, so the masses
are different.
• 14C is radioactive.
14C
• Radioactive 14C acts chemically just like
12C, so it becomes incorporated into plants
an animals.
• When the animal/plant dies the 14C begins
to decay into 14N at a know rate, so we
can determine how long ago the organism
died.
• This is called Carbon Dating.
• It’s only good for about 50,000 years.
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• The half life of 14C is 5,730 years.
• If a sample originally contained
100 g, how much would be left
after 11,460 years?
50g
25g
Older Dating Methods
• The isotopes 235U and 238U
can be used to date
objects billions of years
old.
• 235U has a half life of 704
million years.
• 238U has a half life of 4.5
billion years.
• Mainly used for rocks.
Geiger Counter
• Used to
measure
radiation.
• The more
intense the
radiation the
more “clicks”.