Fission & Fusion
Forces
• What holds an atom together?
• Why doesn’t the nucleus of an atom fly
apart if it’s made of positively charged
protons?
Forces
• Strong Nuclear Forces hold the nucleus of
an atom together.
Who discovered radioactivity?
• In 1896, Henri Becquerel
accidentally left pieces of
uranium salt in a drawer on a
photographic plate. When he
developed the plate, he saw an
outline of the uranium salt on it.
He realized that it must have
given off rays that darkened
the film.
Who discovered radioactivity?
• Two years later
Marie and Pierre
Curie discovered
two new
elements,
Polonium and
Radium, both
radioactive.
Who discovered radioactivity?
• Two years later Marie
and Pierre Curie
discovered two new
elements, polonium and
radium, both
radioactive.
• It took them >3 years to
get 0.1g of radium from
several tons of the
mineral pitchblende.
Radioactive Elements
• Any element over atomic number 83 is
radioactive.
• Radioactive materials have unstable nuclei (too
few or too many neutrons).
• When an unstable nucleus decays, it breaks
apart emitting particles and energy as it decays.
• Three types of nuclear radiation:
Alpha particles
Beta particles
Gamma radiation electromagnetic wave
Fission
• The process used to release nuclear energy
by splitting Uranium-235 nuclei is called
fission.
+ ENERGY
What nuclei can split during
nuclear fission?
• Only large nuclei
like U or plutonium
can split apart
during nuclear
fission.
Click on image
for animation
What nuclei can split during
nuclear fission?
• U-236 is so
unstable that it
immediately splits
into barium &
krypton nuclei,
several neutrons &
a large amount of
energy
Fission
• http://www.atomicarchive.com/Movies/Mov
ie4.shtml
• http://holbert.faculty.asu.edu/eee460/fissio
n.html
• Teachers’ Domain: Nuclear Reaction:
Fission
Chain Reaction
• Free neutrons produced by fission can hit
other nuclei emitting more neutrons
repeating the reaction over and over.
• A series of fission reactions is called a
chain reaction.
• Can only be slowed by using materials
that will absorb the neutrons.
• http://www.atomicarchive.com/Movies/Mov
ie1.shtml
Chain Reaction
• An uncontrolled chain reaction releases a
huge amount of energy in a short time &
requires a critical mass of starting
material to produce more reactions.
Nuclear Power
• Nuclear power plants use
fission to produce energy.
• Nuclear power plants are
used in many countries
(France is the leader).
• There are no nuclear
power plants in KY. The
nearest is 199 miles away
in Tenn.
• Ideal location for a
nuclear power plant?
Take this quiz to test your fear of nuclear
power plants. Should you fear?
Fusion
• The sun is powered by nuclear fusion.
• In a nuclear fusion reaction, two small,
light nuclei combine to form one larger,
heavier nucleus.
• Two hydrogen atoms combine under
extreme heat and pressure to form a
helium atom. (H-2 + H-2→He-4)
Fusion
• http://www.atomicarchive.com/Fusion/Fusi
onMov.shtml
• http://holbert.faculty.asu.edu/eee460/fusio
n.html
Fusion
• Why can’t we use the fusion reaction in
nuclear power plants?
- needs lots of energy
- need to overcome electrical forces
- difficult to control
- never been produced in a nuclear power
plant
Fusion
• Why would we want to use the fusion
reaction in a nuclear power plant?
1. Hydrogen is the most common element in
the universe.
2. Could meet energy demands for millions
of years
Let’s Review
• Brightstorm Videos fission and fusion and
quantitative relationship.
• This site is a blog that has good
animations for fusion and fission.
• Quick Engaging animations
How are temperature & fusion
related?
• How can two nuclei get close enough to
combine? They must be moving very fast.
• All nuclei positively charged
• Thus repel each other
• KE must overcome electric force to push
them close enough to combine
• KE increases as temperature increases
• Temp must be millions of °C like Sun &
other stars
How does the Sun produce
energy?
• The Sun, made
mostly of H produces
its energy by fusion
of H nuclei
• 2 protons (H-1) fuse
to make a H isotope
(H-2); then H-1 + H-2
form an isotope of
He-3.
positron
neutrino
Light
light
The emission of a positron or a positive electron is referred
to as beta decay. The positron is accompanied by a
neutrino, a massless and chargeless particle. Positrons
are emitted with the same kind of energy spectrum as
electrons in negative beta decay because of the emission
of the neutrino.
How does the Sun produce
energy?
• To complete the
process, 4 H
nuclei combine
into 1 He nucleus
during which a
small amount of
matter changes
into a huge
amount of energy.
Fusion on the Sun
• The heat & light Earth receives comes
from this process.
• About 1% of the Sun’s hydrogen has been
changed into energy.
• Sun has enough H to continue fusion
reactions for another 5 billion years.
Fusion vs. Fission
• Fusion combines nuclei & fission splits
them apart. Pdf file
• Comparison Chart Fission vs. Fission
Radiation
• Background radiation can come from
– Sun
– Water
– Plants
***Radon is the largest source of radiation in the
earth’s crust.***
Radiation Damage
•
•
•
•
Mutate hemoglobin
Mutate cells, lose function
Destroy immune system
Burn skin, destroy bone
Radioactive Tracer
• What is a radioactive tracer?
- short lived isotope that can be observed
with a sensitive detector
Radioactive Tracer
• How are they used?
- Agriculture – measure water flow
- Medicine – locate tumors
- Medical research – trace drug paths thru
body
- Geology – trace underground water flow