Transcript Radiation_What Is It

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RADIATION
Energy in the form of particles or
electromagnetic waves emitted from
the nuclei of unstable atoms
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RADIATION
 The term really includes all forms of
electromagnetic radiation
 Radio Waves, Infrared, Visible Light
 Ultraviolet, X-rays, -rays
 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 4 amu
Charge = +2
The isotope’s Atomic Mass goes down four;
The Atomic Number goes down two
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 Atomic Number is increased by one 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
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(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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What is a “packet” of light energy that
behaves like a particle?
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25%
Positron
Negatron
Megatron
Photon
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Which form of radiation penetrates the
least?
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Alpha Decay
Beta Decay
Gamma Decay
Delta Decay
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Which radioactive particle increases
the Parent Nucleus’s atomic number?
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Alpha Particle
Beta Particle
Gamma Particle
Delta Particle
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Which form of radiation penetrates the
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Alpha Decay
Beta Decay
Gamma Decay
Delta Decay
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Which particle drops the Parent
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Alpha Particle
Beta Particle
Gamma Particle
Delta Particle
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Which particle resembles a Helium
nucleus?
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Alpha Particle
Beta Particle
Gamma Particle
Delta Particle
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Which particle isn’t a particle but a
photon?
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Alpha Particle
Beta Particle
Gamma Particle
Delta Particle
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Participant Scores
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Decay Systems
• Each radioactive element will undergo various
forms of radiation until it becomes stable
• The particular elements that a “Parent
Nucleus” changes into are always the same
• This “path” is a Decay System
Half-life
• The amount of time it
takes for HALF of an
amount of a radioactive
material to decay
• One symbol for half-life
is  (lambda)
Original
Amount
# of 
Current
Amount
100g
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50g
100g
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25g
100g
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12.5g
100g
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6.25g
100g
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3.125g
A Decay System
showing half-lives
Nuclear Processes
• Fission
– The splitting of a large, unstable nucleus into two
or more stable nuclei
– Scientists can cause fission by injecting a neutron
at high speed
– This are the uses associated with nuclear fission:
• Power plants / reactors
• Bombs
• “Dirty bombs”
Nuclear Processes
• Fusion
– The joining of two or more smaller nuclei into one
larger, more stable nucleus
– Scientists are working on fission using high
pressures, temperatures, and lasers
– The only place that fusion occurs naturally is stars
TERMS TO REVIEW
Radiation
Alpha particle
Negatron
Positron
Gamma ray
Positive beta decay
Antineutrino
Mother Nucleus
Fission
Alpha decay
Radioactive decay
Negative beta decay
X-ray
Photon
Half-Life
Decay Systems
Daughter Nuclei
Fusion
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