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10/24/16
WARMUP
1. What type(s) of radioactive decay cause the
atomic number of an element to change?
2. What type(s) of radioactive decay cause the
mass of an element to change?
Get out Homework for Ms. Spencer to check!
(Pg. 35 and 17-19 (up to half-life))
NOTES:
HALF-LIFE
• Time it takes for half of
the atoms in a sample to
decay
• Can be anywhere from
billions of years for very
stable isotopes to
millionths of a second
Think of this as a probability-during
for unstable ones
each half-life, all atoms have a 50%
chance of decaying.
RADIOACTIVITY AS A CLOCK
Since the decay rate of an isotope is
constant, we can use it as a sort of clock to
see how old things are.
IF YOU START WITH 100
How many half lives until just
50 remain?
25 remain?
12.5 remain?
IF YOU START WITH 100 HOW MANY
REMAIN AFTER 5 HALF LIVES?
FINISH PAGE 19-20
NUCLEAR
REACTIONS
EQ
What are nuclear fusion and
fission, and what are they
used for?
The Atom
The atom consists of two parts:
1. The nucleus which contains:
protons
neutrons
2. Orbiting electrons.
The Atom
What holds the nucleus together?
Strong Force
1. The nucleus which contains:
protons
neutrons
2. Orbiting electrons.
What keeps the electron orbiting?
Electromagnetic Force
Most of the isotopes which occur naturally are stable.
A few naturally occurring isotopes and all of the manmade isotopes are unstable.
Radioactive decay when unstable isotopes can
become stable by releasing different types of particles.
Radioactive Decay
Radioactive decay results in the
emission of either:
•
an alpha particle (a),
•
a beta particle (b),
• or a gamma ray(g).
Alpha Decay
Alpha Particle:
An alpha particle contains 2 protons and 2 neutrons
Alpha Decay
222
226
Ra
88
Rn
86
4
He
2
HOW CAN ALPHA
PARTICLES HARM YOU?
Think of alpha particles like bowling balls moving in
slow motion – they may not penetrate deeply but
they can do lots of damage to whatever they hit.
Released inside the human body, they can damage
cells causing illness & disease.
Alpha Particles: Can be stopped by paper
Beta Decay
Beta decay, the nucleus has one less
neutron, but one extra proton.
The atomic number increases by 1 and
the mass number stays the same.
Beta Decay
218
218
Po
84
At
85
b (electron)
HOW CAN BETA
PARTICLES HARM YOU?
Beta Particles are faster than alpha because
they’re smaller & lighter so they penetrate
deeper into material they hit.
•Pass through paper and skin
•Aluminum foil will stop a beta particle
•Can damage human cells if released inside the
body
Gamma Decay
Gamma rays are not charged particles like a and b particles. They
are electromagnetic radiation with very high energy
When atoms decay by emitting a or b particles to form a new
atom, the nuclei of the new atom formed may still have too much
energy to be completely stable.
Gamma radiation can be stopped by lead.
Electromagnetic Spectrum
Most radiation comes from natural sources
Sun releases cosmic rays
Radioactive isotopes in sun, air, soil, and
plants
Most organisms can survive in these low
levels of radiation
Beneficial Uses of Nuclear Radiation
-Smoke detectors: release charged alpha
particles to produce electricity
-disease detection
*ultrasounds, CT scanning, MRI
*Radiotherapy for cancer patients
-agriculture: radioactive tracers and
radioisotopes used to look at nutrient and
water flow
Harmful activities that increase nuclear
radiation
-Smoking
-flying more than 720 hours (airline crew)
-X rays: ionize atoms
NUCLEAR FUSION
Nuclear Fusion: The combining of atomic nuclei to form
a larger atom is called fusion
Nuclear fusion occurs in the sun where hydrogen atoms
1 helium
fuse to form
NUCLEAR FUSION
FUSION
Fusion reactions also release very large amount of
energy but require extremely high temperatures to
start.
Nuclear fusion also occurs in new stars and is how
all of our elements were made.
4
2 He
4 He
2
4
+2
8
+4
He 
Be 
8
Be
4
+ energy
12
C
6
+ energy
NUCLEAR FISSION
Nuclear Fission: The splitting of a
nucleus into smaller fragments is called
nuclear fission. This releases lots of
energy
Heavy atoms (mass number>60) tend to break into smaller
atoms, thereby increasing their stability.
NUCLEAR FISSION
NUCLEAR FISSION
More
neutrons
Neutron
Uranium
nucleus
Unstable
nucleus
New nuclei
(e.g. barium
and krypton)
CHAIN REACTIONS
Each fission reaction releases
neutrons that are used in
further reactions.
A chain reaction can only occur if the starting material
has enough mass to sustain a chain reaction. This
amount is called the critical mass.
Nuclear Fission is what occurs in Nuclear Reactors and
Atomic Bombs.
The Nuclear reactor is a controlled fission reaction, the
bomb is not.
NUCLEAR POWER PLANT
HOW NUCLEAR POWER WORKS
WHAT ARE THE MAIN PARTS?
FILL OUT YOUR NOTES REVIEW
SHEET
WHEN DONE FOLD IN HALF AND
GLUE IN NOTEBOOK
NUCLEAR POWER PROJECT
Odd Periods: November 2nd
Even Period: November 3rd
You may work alone or with a partner
1st: Research Nuclear Power pg. 25-27