• a nucleus is made up of protons (positively charged particles) and neutrons (neutral particles)
• the number of protons in a nucleus determines what element that atom is. (ie. All Carbon atoms have 6 protons)
• the neutrons make it possible for the nucleus to stick together, and are responsible for isotopes
• isotopes are types of the same element (same # of protons), with different atomic mass numbers (due to the # of neutrons present).
• Carbon 12 has 6 protons + 6 neutrons
• Carbon 14 has 6 protons + 8 neutrons
• a nucleus is radioactive when it is unstable and can spontaneously emit a particle and become the nucleus of another element
• all elements heavier than Bismuth decay in one way or another
• different radioactive nuclei decay at different rates, the time it takes for ½ of the material to decay is known as the half-life
• for some nuclei the half-life may be a fraction of a second, while for others it is millions of years
• they emit three distinct types of rays, alpha, beta and gama rays
• alpha particle -
• positive charge
• contain two protons and two neutrons (He nucleus)
• stopped by a heavy piece of paper
• quickly slows down, grabs a couple electrons and becomes a stable He atom
• beta particle
• negative charge
• electron (emitted from a nucleus when a neutron is transformed into a proton + electron + antineutrino)
• stopped by several sheets of aluminum foil
• gamma ray
• massless energy (electromagnetic radiation) just like an x-ray or visible light, but with very high frequency and energy
• stopped by thick layer of lead

• when a transmutation occurs the total atomic number and total atomic mass number of all particles involved in the reaction do not change
• it appears that mass and electric charge are conserved
• however, under very careful observation, it is found that the mass of the reactants is slightly less than the mass of the products
• in any chemical or nuclear reaction energy and mass must be conserved
• huge amounts of energy are generated from some nuclear reactions
• where does it come from? And where does the mass go?
• It appears as though energy is created and mass disappears - this is not possible
• Einstein proposed in the ‘theory of relativity’ that mass is another form of energy.
• A decrease in mass of one object might show up as an increase in energy

• Energy comes from the conversion of nuclear mass into energy is called nuclear energy

Calculate the amount of energy produced when 1.0 kg mass is completely transformed into energy.

E = mc²

= (1.0 kg)(3.00 x 10⁸ m/s)²

= 9.0 x 10¹⁶ Joules

A nuclear reaction produces 9.0 x 10¹¹ J of heat energy because of the conversion of mass into energy. What mass was converted?

E = mc²

m = E /c²

= 9.0 x 10¹¹ J / (3.00 x 10⁸ m/s)²

= 1.0 x 10^-5 kg or 1.0 x 10¹ mg

• fission - splitting of a heavy atoms into lighter atoms
• must be done with a neutron (it can approach the positive nucleus closely)
• most commonly done with Uranium 235
• accompanied by the release of about 10 times as much energy as occurs in normal nuclear disintegration and one million time as much as any chemical reaction
• the energy released by the fission of one Uranium 235 atom is seven million times the energy released by one TNT molecule.

• each reaction releases other neutrons from the Uranium 235 that was hit
• these neutrons can cause fission in other Uranium 125 atoms, releasing more neutrons, and as it continues more and more nuclei undergo fission releasing larger and larger numbers of neutrons and energy. This is called a chain reaction.

• Natural Uranium is 99.3% Uranium 238, 0.7% Uranium 235, and traces of Uranium 234
• Uranium 235 is the only fissionable isotope of Uranium
• in a regular sample of natural uranium, it is unlikely that a neutron will hit a Uranium 235
• enrichment is done to increase the proportion of Uranium 235
• to sustain a chain reaction, there must be enough Uranium 235 that the number of neutrons produced exceeds the number lost from the surface and to impurities.
• This amount of Uranium 235 is called critical mass
• when critical mass is present, the chain reaction proceeds without any outside assistance

• the chance of a successful collision with a Uranium 235 is increased if the neutron is moving slowly.
• Fast moving neutrons are deflected around the nucleus
• substances used to slow down neutrons are moderators
• atoms with low atomic mass such as graphite, water or heavy water are good moderators
• (they slow neutrons down without absorbing them)

• the rate of a chain reaction is controlled by inserting substances that absorb neutrons (Boron or Cadmium) into the enriched Uranium
• these ‘control rods’ can be moved in and out to control the rate of the reaction, or stop it altogether

In a nuclear bomb, there are no control rods and the chain reaction goes, in a fraction of a second, enormous amounts of energy, fast moving neutrons and gamma radiation are released.

• nuclear energy can be harnessed in a much more gentle way by using a nuclear reactor.
• CANDU Reactor
• Pressured Water Reactor
• Gas Cooled Reactor
• Fast Breeder Reactor

• problems storing radioactive wastes
• production of plutonium and danger of nuclear weapons
• low-level release of radioactive materials into air and groundwater
• risk of accidental release of large amounts of radioactivity

• occurs in stars
• energy is gained as light nuclei fuse or combine, rather than split apart
• energy is released when heavy nuclei split, but in fusion, energy is released when light nuclei fuse together
• after fusion, the total mass of the light nuclei formed is less than the total mass of the nuclei that fused.
• For fusion to occur nuclei must hit as very high speed to overcome the repulsion of the (+) charges
• for speeds this high, temperatures must be extremely high (hundreds of millions of degrees)
• must use a magnetic field to ‘hold’ the reaction, because all material containers will melt and vaporize.
• The trick is to get a reaction that will be stable and self sustaining, so that no more energy has to be put in. This has not been accomplished.
• Another possibility is dropping frozen hydrogen pellets into the crossfire of multiple laser beams.
• Once fusion is possible, it will be an incredible breakthrough for humanity
• the reaction cannot get out of control, because there is no ‘critical mass’
• no air pollution, the only product is Helium
• no radio active material are formed
• fuel is hydrogen, the most abundant element in the universe
• 30 liters of seawater has 1 gram of deuterium which will release energy equivalent to 10 000 liters of gasoline or 80 tons of TNT