Take a large atom and impact the
nucleus with a particle.
 Split the atom releasing high energy,
more high energy neutrons, and two
daughter nuclides.
 Fission occurs only rarely in nature.
Alpha decay is much more common.

Elements with an atomic number greater
than 80 are capable of undergoing
fission.
 23592U absorbs a neutron, 10n, temporarily
producing unstable 23692U.
 Almost immediately 23692U splits into two
more stable daughter nuclides plus large
amounts of energy and two to three fast
neutrons depending on the reaction.

The fast neutrons produced by fission fly
off to impact other atoms of 23592U
resulting in a chain reaction.
 The fission of uranium-235 releases
~200MeV. That equals ~100x energy
release by burning a coal molecule.
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Fissile: atoms (235U or 239Pu)that are capable of
undergoing fission when an atom captures a thermal
slower neutron.
Fissionable: atoms (238U)able to undergo fission when
bombarded with high energy neutrons such as in a
thermonuclear weapon, bomb.
Nuclear fuels: elements that can sustain a fission
chain reaction such as uranium-235 and plutonium239.
Spontaneous fission: the slowly occurring process of
fission in nuclear fuels unaltered by human
intervention.
Critical mass: enough nuclear fuel present and
emitting neutrons in quantities to sustain a chain
reaction.
Once the fission reaction is initiated, the
high energy neutrons released keep the
reaction going. This is a chain reaction.
 The mousetrap model.

› http://www.youtube.com/watch?v=0v8i4v1
mieU Student project 2:54 minutes
› http://www.youtube.com/watch?v=vjqIJW_
Qr3c NatSciDemo 2:28 minutes
A coal fired plant and a nuclear plant
share the same power generation type:
conversion of heat to electricity via
pressurized steam.
 The fission reaction releases energy
which is absorbed by water converting
some of the water to steam.
 Steam is used to drive the turbine
connected to a generator.

http://www.youtube.com/watch?v=CGRx
2cPjUXM Navy Film of Bikini Crossroads
Test
A bomb typically uses a contained
explosion or impact to induce a chain
reaction. No controls limit the progress of
the reaction.
Fusion reactions are the combining of
two nuclei to form a more massive
nucleus.
 Many fusion reactions release large
amounts of energy.

› An example is the combining of two isotopes
of hydrogen (tritium and deuterium) to form
helium and a neutron plus a large amount of
kinetic energy in the reaction products:
3H + 2H  4He + n + 17.6 MeV

http://www.youtube.com/watch?featur
e=endscreen&v=yTkojROgt8&NR=1&safety_mode=true&persist_saf
ety_mode=1&safe=active Best of
Science, Fission and Fusion 8:38 minutes

http://www.lbl.gov/abc/wallchart/teach
ersguide/contents.html DOE Teacher’s
Guide