Nuclear Energy
A. What does “radioactive” mean?
1. Radioactive materials have
unstable nuclei, which go through
changes by emitting particles or
releasing energy to become stable
a. Call this nuclear decay
B. Types of Radiation
1. Nuclear Radiation: the particles that are
released from the nucleus during
radioactive decay
a. When a radioactive nucleus decays,
the radiation leaves the nucleus
b. IMPORTANT
This may form an
isotope of the same element or make
a new element
Types of radiation
•
•
•
•
1.
2.
3.
4.
Alpha particle
Beta particle
Gamma ray
Neutron
2. Alpha Particle: a positively charged
particle that consists of 2 protons and 2
neutrons (2P + 2N)
a. + charged
b. Most massive- Do not travel far
through materials (cannot pass
through a piece of paper)
c. Symbol: 42He
d. Ex. Uranium-238 is radioactive and
releases alpha particles
Alpha Particle
3. Beta Particle: a negatively (-) charged
electron emitted during radioactive decay
a. Fast-moving electron- MADE FROM A
NEUTRON THAT DECAYS & FORMS A
PROTON AND A eb. THE PROTON STAYS AND THE e- LEAVES
THE ATOM
c. Can penetrate sheet of paper, but stopped
by 3 mm of aluminum
d. Symbol: 0-1e
Beta Particle
4. Gamma Rays: high-energy radiation emitted
during radioactive decay and nuclear fission
-Marie Curie- isolated radium & saw it emitted
gamma rays
a. Gamma rays are a form of electromagnetic
energy so they are “not charged” and “not
made of matter”
b. Not stopped by clothing or most building
materials, (can penetrate up to 60 cm of Al or
7 cm of Pb) so are much more dangerous
c. Symbol: γ
Gamma Rays
Neutron Emission
• No charge;
• Need 15 cm Pb to stop
fast moving neutrons
Nuclear Decay
• When an unstable nucleus emits alpha or beta
particles; # of P & # N changes
• Alpha Decay- lose 2 P + 2 N (same as He
atom)- causes the mass number to decrease
by 4 & the atomic number to decrease by 2
• Example: The process of alpha decay of
radium-226 is written as follows.
226
222 Rn +
Ra
→
88
86
4
2He
Nuclear Decay
• Beta Decay- gain 1 P + lose 1 N (remember a
neutron decays to form 1 P & 1 e- (the proton
stays and the e- leaves)
• Example: Carbon-14 decays to nitrogen-14 by
emitting a beta particle
•
14
14 N + 0 e
C
→
6
7
-1
• Gamma Ray decay- no change in # P; energy
content changes in the matter it hits
C. Decay Rates
1. Half-life: time required for half of a sample of
radioactive substance to decay
-1st half life = ½ sample remains
-2nd half life = ½ x ½ = ¼ sample remains
-3rd half life= ½ x ½ x ½ = 1/8 sample remains
2. Use these decay rates to tell the age of rocks
and fossils (radiometric dating)
a. Carbon-14 is common isotope used in
radiometric dating
Nuclear Reactions
• Strong Nuclear Force- force that causes
protons & neutrons to attract each other in
the nucleus
• Protons are + and repel each other
• Neutrons have no charge so they help create
the strong nuclear force to hold protons &
neutrons together in the nucleus
Nuclear Reactions
• Stable Nuclei- strong nuclear force is stronger
than the repulsion force
• Unstable Nuclei- strong nuclear force is less than
the repulsion force
A. Have too many or too few neutrons in
nucleus
B. Have more than 83 protons in nucleus
C. Will decay (and release radiation) into a
more stable nucleus
II.) Nuclear Reactions
A) Nuclear Fission: the process by which a
nucleus splits into two or more smaller
atoms and releases neutrons and
energy
1. In nuclear fission, tremendous
amounts of energy can be produced
from very small amounts of mass (Fig.
7 p.295)
Nuclear Fission
•
235 U
92
+ 10n → 13756 Ba + 8436 Xe + 15 10n + energy
2. Converting Mass into Energy
a. Albert Einstein introduced the mass-energy
equation:
2
E = mc
b. According to the law of conservation of
mass and energy, the total amount of mass
and energy remains constant
c. Mass defect- the total mass of any nucleus
measured is less than the sum of the
individual masses of protons & neutrons
that form it; SOME OF THE MASS HAS
TURNED INTO ENERGY!!
Converting Mass into Energy
• The amount of energy released during nuclear
fission is related to the mass that is turned
into energy
•
E = mc2
3. Triggering a Nuclear Chain Reaction
a. Nuclear fission follows a pattern of a chain
reaction; The speed of a chain reaction can vary
b. Chain reaction: a continuous series of nuclear
fission reactions [Fig 8 p.296]
c. Nuclear fission releases more
neutrons which trigger more fission
reactions
d. The number of neutrons released
determines the success of a chain
reaction
Nuclear Chain Reaction
c. Nuclear weapons- ex. Atomic bombs (use U-235
or Pu-239) are designed to have an uncontrolled
chain reactions
d. Nuclear Power Plants- A controlled chain
reaction, heat from the reaction can be used to
generate electrical energy
-controls chain reaction with control rods that
absorb neutrons emitted after fission reaction
c. Critical Mass: the minimum amount of a
substance that can undergo a fission reaction
and can also sustain a chain reaction.
4. Nuclear Energy From Fission
a. Nuclear power plants generate
about 20% of electricity in the U.S.
b. Controlled fission of uranium-235 in
a fission reactor
c. Don’t emit air pollutants, but have
other safety concerns
d. 1986: meltdown of reactor at
Chernobyl nuclear power plant in
Ukraine
B. Fusion: the process in which smaller nuclei
fuse together at extremely high
temperatures and release energy (occurs in
stars like the sun)
C. Light nuclei combine to form heavy
nuclei
1. In nuclear fusion, tremendous amounts
of energy can be produced from very
small amounts of mass
2. THE FUSION OF HYDROGEN RELEASES
MORE ENERGY THAN THE BURNING OF
NATURAL GAS, BURNING OF COAL, OR
THE FISSION OF URANIUM-235!!
Fusion
• Nuclear fusion plants using hydrogen may be a
possibility one day
• 1 pound of hydrogen in a fusion reactor may
release as much energy as 16 million pounds
of burning coal!!
Fusion Reaction
.
2H + 3 H  4He + 1n
1
1
2
0
3. Requires extremely high
temperatures—i.e. Sun reaches
temp of 10,000,000oC
-need a lot of energy to overcome
repulsion force of protons
3. Fusion may someday provide clean
and efficient source of electricity
5. Two problems creating a fusion
reactor:
a. Need very high temperatures
to start reaction
b. Must contain plasma
Nuclear Radiation Today
• Background Radiation- all around us; comes from
natural sources like the sun, plants, water, heat, soil,
rocks, etc. ( due to the fact that radioactive isotopes
live there)
• Exposure varies from one location to another
• ex. Living in higher altitudes or around rocks
increases radiation exposure
• -Also, things like smoking, getting x-rays
Beneficial Uses of Radiation
• 1. Smoke detectors- release alpha particles which
are charged & release an electric current, smoke
decreases the flow of current which sets off the
alarm
• 2. Used to detect disease• A). X-rays
• B). MRI
• C). Radioactive tracers- isotopes that
concentrate in affected areas to locate tumors
Nuclear Radiation is used to treat cancer
• Radiotherapy- is a treatment that uses controlled
doses of nuclear radiation for treating diseases such
as cancer
• Ex. A) Brain tumor- uses gamma rays to treat
them
•
B) iodine isotopes treat thyroid cancer
•
C) Radiation is used to kill defective bone
marrow of leukemia patients
• Agriculture- radioactive tracers move through crops
to see how fast water moves through them.