Radioactivity
A MOLE
Early Pioneers in Radioactivity
Rutherford:
Roentgen:
Discoverer Alpha
and Beta rays 1897
Discoverer of Xrays 1895
The Curies:
Discoverers of
Radium and
Polonium 1900-1908
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Becquerel:
Discoverer of
Radioactivity 1896
What is Radioactivity and Radiation?
• Radioactive decay is the process in which an unstable atomic
nucleus loses energy by emitting radiation in the form of
particles or electromagnetic waves.
• 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.
Why?
• the nucleus of an atom attempts to become more stable
The Nuclear Stability Belt
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Geiger Counter
• Used to measure
radiation.
• The more intense
the radiation the
more “clicks”.
Kinds of Radioactivity
The three main decays are Alpha, Beta and Gamma
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Nuclear Decay
Alpha Particles and Alpha Decay
• 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.
Beta Particles and Beta Decay
• 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 decays into a proton.
Gamma Rays and Gamma Radiation
• Gamma rays are a form of electromagnetic radiation 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.
Three Common Types of Decay
Alpha
Beta
Gamma
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Three Common Types of Radioactive Emissions Penetrability
Alpha particles may be
completely stopped by a
sheet of paper, beta
particles by aluminum
shielding. Gamma rays,
however, can only be
reduced by much more
substantial obstacles,
such as a very thick piece
of lead.
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Radioactivity – Is it a Health
Problem?
• The Alpha, Beta and Gamma particles all add
energy to the body’s tissues. The effect is called
the Ionizing Energy. It can alter DNA.
• Even though Alpha particles are not very
penetrative if the decaying atom is already in the
body (inhalation, ingestion) they can cause
trouble.
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Sources of Radioactivity
• Primordial - from before the creation
of the Earth
• Cosmogenic - formed as a result of
cosmic ray interactions
• Human produced - enhanced or
formed due to human actions (minor
amounts compared to natural)
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Where are the Sources of
Radioactivity?
• Naturally Occurring Sources:
• Radon from the decay of Uranium and Thorium
• Potassium -40 – found in minerals and in plants
• Carbon 14 – Found in Plants and Animal tissue
• Manmade Sources:
• Medical use of Radioactive Isotopes
• Certain Consumer products –(eg Smoke detectors)
• Fallout from nuclear testing
• Emissions from Nuclear Power plants
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Radiation is used positively in a variety of ways
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.
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.
Radiation Exposure to Americans
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Your Personal Annual Radiation Dose
• Environmental Protection Agency
• Radiation has existed everywhere in the environment since
the Earth's formation in rocks, soil, water, and plants. The
mining and processing of naturally occurring radioactive
materials for use in medicine, power generation, consumer
products, and industry inevitably generate emissions and
waste. Recognizing the potential hazards of these activities,
Congress designated EPA as the primary federal agency
charged with protecting people and the environment from
harmful and avoidable exposure to radiation.
• http://www.epa.gov/rpdweb00/understand/calculate.html
Half-Life
The half-life of a radioactive substance, is the time required
for one half of it to decay.
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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.
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.
Nuclear Decay Equations
mass #Reactant
atomic #
 mass #Products + …
atomic #
2H
1
Alpha Decay
210
84
Po 
A
Z
X + He
4
2
Beta Decay
140
56
Ba 
A
Z
X + e0
-1
More Nuclear Decay Equations