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RADIATION
Energy in the form of particles or
electro-magnetic waves emitted from
the nuclei of unstable atoms
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RADIATION
 The term really includes all forms of
electromagnetic radiation
 Commonly used today to describe
particulate radiation
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NUCLEAR REACTIONS
PRODUCE RADIATION
 Protons and neutrons determine
nuclear reactions
 One must understand atomic structure
to understand radiation
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NUCLEAR PARTICLES
Protons and Neutrons are the two basic
nuclear particles. Together they contain
practically all the mass of an atom and
are determinants of an atom’s nuclear
characteristics.
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RADIOACTIVE DECAY
• Radioactive decay refers to the spontaneous
emission of radiation from the nucleus of an
unstable atomic nucleus
• The ratio of neutrons to protons is largely
determinant of the stability of the nucleus
and the tendency for radioactive
decay to occur
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DEFINITION OF
RADIOACTIVE DECAY
“Radioactive decay is the process of
spontaneous emission of radiation in the
form of particles or photons from the
nuclei of unstable atoms”
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CHARACTERISTICS OF
RADIOACTIVE DECAY
• It is a natural process in our universe
• It is spontaneous – we cannot predict when
an atom will undergo decay
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BASIC TYPES OF
RADIOACTIVE DECAY
Alpha () decay
• Occurs when atomic nuclei have too many
protons and neutrons (i.e., Are heavy)
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ALPHA PARTICLE
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CHACTERISTICS OF
ALPHA PARTICLES
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Consist of 2 protons and 2 neutrons
Mass of an alpha particle is ~8000 me or 4 amu
Charge = +2
Are highly ionizing
Have low penetrating abilities
(only cm in air and mm in water)
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MORE ABOUT
ALPHA PARTICLES
• Easily shielded; common types of shielding
are paper, cardboard, air, clothing; will not
penetrate skin
• Health hazard when taken internally
• Not commonly used in medicine
• Common sources = smoke detectors
(Am-241) and lantern mantles (thorium nitrate)
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ALPHA PARTICLE DECAY
• Changes both the mass and identity of
the nucleus of the parent radionuclide
• This means that the decay results in the
formation of a new element as the
daughter product
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QUESTIONS?
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NEGATIVE BETA (ß-) DECAY
Occurs when atoms have too many neutrons
(i.e., Are “neutron-rich”) and decay by emitting a
negative beta particle (ß-)
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WHAT ARE NEGATIVE BETA
PARTICLES?
During negative beta decay, excess neutrons are
converted into protons, electrons, and antineutrinos.
The protons remain in the nucleus but the new
electrons are emitted as negative beta particles (ß-)
or negatrons. You may
wish to think of them as
“nuclear electrons.”
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CHARACTERISTICS OF
NEGATIVE BETA DECAY
• Less ionizing than alphas due to decreased mass
of negatrons
• Changes the identity of the nucleus but not the mass
• The z number is increased due to
conversion of neutrons
into protons
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CHARACTERISTICS OF NEGATIVE
BETA PARTICLES (NEGATRONS)
Negatrons consist of nuclear electrons
The mass is the same as electrons
There is a charge of –1 in negatrons
More penetrating than alpha particles;
~ 12 meters in air
 They can penetrate skin–
best shielding is wood,
plastics, thick
cardboard, etc.
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POSITRON
+
(ß )
EMISSION
Occurs when the nucleus of the atom has too
many protons (i.e., is proton-rich). It is also
known as positive beta decay.
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POSTIVE
+
BETA (ß )
DECAY
Results in a positive electron emitted from the nucleus
of the proton rich atom. This positive electron is known
as a positron. An additional particle, a neutrino, is also
emitted from the nucleus. Neutrinos are very small
particles with no electric charge.
They have little or no
mass and participate in
weak interactions.
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CHARACTERISTICS OF
POSITRON EMMISION
Positrons have same mass as electrons
Positrons have charge +1
Positrons are less ionizing than alphas
Positrons are more penetrating than alpha decay
but less than gamma
 The best shielding is lead
with thickness of 1 inch
or more
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QUESTIONS?
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GAMMMA () EMISSION
Is a form of pure electromagnetic radiation emitted
from nuclei that have excess energy. It is
sometimes called gamma photon radiation.
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GAMMMA RAYS
Are photons emitted from unstable nuclei to rid
themselves of excess energy.
Gamma photons are subatomic packets of pure
energy. They are higher in energy and more
penetrating than the
photons that make
up visible light.
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GAMMMA RAYS AND X RAYS
Have the same properties except for their origin
Gammas come from within the nuclei of atoms
X-rays come from outside the nuclei
Both are
electromagnetic
energy in the form
of emitted photons
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PROPERTIES OF GAMMMA ()
AND X RAYS
 Charge is 0 (no charge)
 Mass is 0 (no mass)
 Low ionization
 Penetration abilities can be extremely high; –
penetrating power is
dependent upon the
energy of the
emitted photons
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QUESTIONS?
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TERMS TO REVIEW
Radiation
Alpha particle
Negatron
Positron
Gamma ray
Positive beta decay
Antineutrino
Alpha decay
Radioactive decay
Negative beta decay
X-ray
Photon
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TEST YOUR KNOWLEDGE
#1
Which of the following particles has the most mass?
A. Negatron
B. Gamma photon
C. Positron
D. Alpha
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TEST YOUR KNOWLEDGE
#2
Which of the following does not penetrate human skin?
A. Alpha radiation
B. Positron emission
C. X-rays
D. Gamma rays
E. Negatron radiation
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TEST YOUR KNOWLEDGE
#3
Radioactive decay is a spontaneous process.
A. True
B. False
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TEST YOUR KNOWLEDGE
#4
Which of the following has no mass and no charge?
A. Alpha particles
B. Gamma rays
C. Negative beta particles
D. Positrons
E. No correct answer given
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TEST YOUR KNOWLEDGE
#5
What type of radioactive decay occurs because of
proton rich nuclei?
A. Gamma
B. Positive beta
C. Alpha
D. Negative beta
E. X-ray
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Want to Know More????
Arrange a visit to a nearby Nuclear Facility or
search the WWW.
Farley Nuclear Plant Visitors Center
near Dothan, AL
1-800-344-8295
http//:www.southerncompany.com
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