Nuclear Fission and Nuclear Fusion

Enormous Energies

Nuclear Fission 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.

Uranium-235 Elements with an atomic number

greater than 80 are capable of undergoing fission.

23592U absorbs a neutron, 1

0n, temporarily producing unstable 236

92U. Almost immediately 236

92U splits into two more stable daughter nuclides plus large amounts of energy and two to three fast neutrons depending on the reaction.

Fission and energy 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.

Concepts 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 plutonium-239.

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.

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=0v8i4v1mieU Student project 2:54 minutes

› http://www.youtube.com/watch?v=vjqIJW_Qr3c NatSciDemo 2:28 minutes

Power Production 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.

Schematic of Nuclear Plant

The Bombhttp://

www.youtube.com/watch?v=CGRx2cPjUXM 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 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?feature=endscreen&v=yTkojROg-t8&NR=1&safety_mode=true&persist_safety_mode=1&safe=active Best of Science, Fission and Fusion 8:38 minutes

Resources http://

www.lbl.gov/abc/wallchart/teachersguide/contents.html DOE Teacher’s Guide